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The radiation pattern of an antenna is a plot of the relative field strength of the radio waves emitted by the antenna at different angles. It is typically represented by a three dimensional graph, or polar plots of the horizontal and vertical cross sectionsLenovo S10-2 Battery 5200mAh.

The pattern of an ideal isotropic antenna, which radiates equally in all directions, would look like a sphere. Many nondirectional antennas, such as monopoles and dipoles, emit equal power in all horizontal directions, with the power dropping off at higher and lower anglesLenovo Y730 Battery 5200mAh;

this is called an omnidirectional pattern and when plotted looks like a torus or donut.

The radiation of many antennas shows a pattern of maxima or "lobes" at various angles, separated by "nulls", angles where the radiation falls to zero  Lenovo Y710 Battery 5200mAh.

This is because the radio waves emitted by different parts of the antenna typically interfere, causing maxima at angles where the radio waves arrive at distant pointsin phase, and zero radiation at other angles where the radio waves arrive out of phase  Lenovo Y530 Battery 5200mAh.

In a directional antenna designed to project radio waves in a particular direction, the lobe in that direction is designed larger than the others and is called the "main lobe". The other lobes usually represent unwanted radiation and are called "sidelobes". The axis through the main lobe is called the "principle axis" or "boresight axis"Lenovo Y510 Battery 5200mAh.

Impedance

As an electro-magnetic wave travels through the different parts of the antenna system (radio, feed line, antenna, free space) it may encounter differences in impedance (E/H, V/I, etc.)  Lenovo S10-3 Battery 5200mAh.

At each interface, depending on the impedance match, some fraction of the wave's energy will reflect back to the source, forming a standing wave in the feed line. The ratio of maximum power to minimum power in the wave can be measured and is called the standing wave ratio(SWR)  Lenovo G450 Battery 5200mAh.

A SWR of 1:1 is ideal. A SWR of 1.5:1 is considered to be marginally acceptable in low power applications where power loss is more critical, although an SWR as high as 6:1 may still be usable with the right equipment  Lenovo E30 Battery 5200mAh.

Minimizing impedance differences at each interface (impedance matching) will reduce SWR and maximize power transfer through each part of the antenna system.

Complex impedance of an antenna is related to the electrical length of the antenna at the wavelength in use  Lenovo E40 Battery 5200mAh.

The impedance of an antenna can be matched to the feed line and radio by adjusting the impedance of the feed line, using the feed line as an impedance transformer. More commonly, the impedance is adjusted at the load (see below) with an antenna tuner, a balun, a matching transformer  Lenovo E50 Battery 5200mAh,

matching networks composed of inductors and capacitors, or matching sections such as the gamma match.

Efficiency

Efficiencyis the ratio of power actually radiated to the power put into the antenna terminals  Lenovo G460 Battery 5200mAh.

A dummy load may have an SWR of 1:1 but an efficiency of 0, as it absorbs all power and radiates heat but very little RF energy, showing that SWR alone is not an effective measure of an antenna's efficiency. Radiation in an antenna is caused by radiation resistance which can only be measured as part of total resistance including loss resistanceLenovo Y460 Battery 5200mAh.

Loss resistance usually results in heat generation rather than radiation, and reduces efficiency. Mathematically, efficiency is calculated as radiation resistance divided by total resistance.

Bandwidth

The bandwidthof an antenna is the range of frequencies over which it is effective, usually centered on the resonant frequencyLenovo Y450 Battery 5200mAh.

The bandwidth of an antenna may be increased by several techniques, including using thicker wires, replacing wires with cagesto simulate a thicker wire, tapering antenna components (like in a feed horn), and combining multiple antennas into a single assembly (array) and allowing the natural impedance of suitable inductive RF filter traps to select the correct antennaLenovo N200 Battery 5200mAh.

All these attempts to increase bandwidth by adding capacitance to the surface area have a detrimental effect on efficiency by reducing the Q factor. They also have an adverse effect on the rejection of unwanted harmonics, on both received and transmitted signal frequencies  Lenovo T410 Battery 5200mAh.

Small antennas are usually preferred for convenience, but there is a fundamental limit relating bandwidth, size and efficiency.

Polarization

The polarizationof an antenna is the orientation of the electric field (E-plane) of the radio wave with respect to the Earth's surface and is determined by the physical structure of the antenna and by its orientationLenovo T510 Battery 5200mAh.

It has nothing in common with antenna directionality terms: "horizontal", "vertical" and "circular". Thus, a simple straight wire antenna will have one polarization when mounted vertically, and a different polarization when mounted horizontally  Lenovo SL410 Battery 5200mAh.

"Electromagnetic wave polarization filters" are structures which can be employed to act directly on the electromagnetic wave to filter out wave energy of an undesired polarization and to pass wave energy of a desired polarization.

Reflections generally affect polarization  Lenovo SL510 Battery 5200mAh.

For radio waves the most important reflector is the ionosphere - signals which reflect from it will have their polarization changed unpredictably. For signals which are reflected by the ionosphere, polarization cannot be relied upon. For line-of-sight communications for which polarization can be relied upon  Lenovo C100 Battery 5200mAh,

it can make a large difference in signal quality to have the transmitter and receiver using the same polarization; many tens of dB difference are commonly seen and this is more than enough to make the difference between reasonable communication and a broken link  Lenovo T400S Battery 5200mAh.

Polarization is largely predictable from antenna construction but, especially in directional antennas, the polarization of side lobes can be quite different from that of the main propagation lobe. For radio antennas, polarization corresponds to the orientation of the radiating element in an antenna  Lenovo Y430 Battery 5200mAh.

A vertical omnidirectional WiFi antenna will have vertical polarization (the most common type). An exception is a class of elongated waveguide antennas in which vertically placed antennas are horizontally polarized. Many commercial antennas are marked as to the polarization of their emitted signals  Ibm ThinkPad G40 Battery 5200mAh.

Polarization is the sum of the E-plane orientations over time projected onto an imaginary plane perpendicular to the direction of motion of the radio wave. In the most general case, polarization iselliptical, meaning that the polarization of the radio waves varies over time  Ibm ThinkPad X200T Battery 5200mAh.

Two special cases are linear polarization (the ellipse collapses into a line) and circular polarization (in which the two axes of the ellipse are equal). In linear polarization the antenna compels the electric field of the emitted radio wave to a particular orientationApple A1280 battery 5200mAh.

Depending on the orientation of the antenna mounting, the usual linear cases are horizontal and vertical polarization. In circular polarization, the antenna continuously varies the electric field of the radio wave through all possible values of its orientation with regard to the Earth's surface  Apple A1281 battery 5200mAh.

Circular polarizations, like elliptical ones, are classified as right-hand polarized or left-hand polarized using a "thumb in the direction of the propagation" rule. Optical researchers use the same rule of thumb, but pointing it in the direction of the emitter, not in the direction of propagation, and so are opposite to radio engineers' use  Samsung R522 battery 5200mAh.

In practice, regardless of confusing terminology, it is important that linearly polarized antennas be matched, lest the received signal strength be greatly reduced. So horizontal should be used with horizontal and vertical with vertical  Samsung P467 battery 5200mAh.

Intermediate matchings will lose some signal strength, but not as much as a complete mismatch. Transmitters mounted on vehicles with large motional freedom commonly use circularly polarized antennas so that there will never be a complete mismatch with signals from other sources  Hp Pavilion dm3 Battery 5400mAh.

Transmission and reception

All of the antenna parameters are expressed in terms of a transmission antenna, but are identically applicable to a receiving antenna, due to reciprocity. Impedance, however, is not applied in an obvious way; for impedance, the impedance at the load (where the power is consumed) is most critical  Hp Pavilion dm4 Battery 5200mAh.

For a transmitting antenna, this is the antenna itself. For a receiving antenna, this is at the (radio) receiver rather than at the antenna. Tuning is done by adjusting the length of an electrically long linear antenna to alter the electrical resonance of the antenna  Hp Pavilion cq62 Battery 5200mAh.

Antenna tuning is done by adjusting an inductance or capacitance combined with the active antenna (but distinct and separate from the active antenna). The inductance or capacitance provides thereactance which combines with the inherent reactance of the active antenna to establish a resonance in a circuit including the active antenna  Hp Pavilion cq42 Battery 5200mAh.

The established resonance being at a frequency other than the natural electrical resonant frequency of the active antenna. Adjustment of the inductance or capacitance changes this resonance  Hp Pavilion cq72 Battery 5200mAh.

Antennas used for transmission have a maximum power rating, beyond which heating, arcing or sparking may occur in the components, which may cause them to be damaged or destroyed. Raising this maximum power rating usually requires larger and heavier components, which may require larger and heavier supporting structuresHp cq20 Battery 2600mAh.

This is a concern only for transmitting antennas, as the power received by an antenna rarely exceeds the microwatt range.

Antennas designed specifically for reception might be optimized for noise rejection capabilities  Hp 2230 Battery 2600mAh.

An antenna shield is a conductive or low reluctance structure (such as a wire, plate or grid) which is adapted to be placed in the vicinity of an antenna to reduce, as by dissipation through a resistance or by conduction to ground, undesired electromagnetic radiation  Dell Inspiron Mini 12 battery 7800mAh,

or electric or magnetic fields, which are directed toward the active antenna from an external source or which emanate from the active antenna. Other methods to optimize for noise rejection can be done by selecting a narrow bandwidth so that noise from other frequencies is rejected  Dell XPS M1730 battery 7800mAh,

or selecting a specific radiation pattern to reject noise from a specific direction, or by selecting a polarization different from the noise polarization, or by selecting an antenna that favors either the electric or magnetic fieldDell XPS M2010 battery 7800mAh.

For instance, an antenna to be used for reception of low frequencies (below about ten megahertz) will be subject to both man-made noise from motors and other machinery, and from natural sources such as lightning. Successfully rejecting these forms of noise is an important antenna featureDell Studio XPS 1340 battery 5200mAh/7800mAh.

A small coil of wire with many turns is more able to reject such noise than a vertical antenna. However, the vertical will radiate much more effectively on transmit, where extraneous signals are not a concern.

Basic antenna models

There are many variations of antennas. Below are a few basic models. More can be found in Category:Radio frequency antenna typesDell Inspiron 9100 battery 7800mAh.

  • The isotropic radiator is a purely theoretical antenna that radiates equally in all directions. It is considered to be a point in space with no dimensions and no mass. This antenna cannot physically exist, but is useful as a theoretical model for comparison with all other antennas  Dell Inspiron N4010 battery 5200mAh.
  • Most antennas' gains are measured with reference to an isotropic radiator, and are rated in dBi (decibels with respect to an isotropic radiator).
  • The dipole antenna is simply two wires pointed in opposite directions arranged either horizontally or vertically, with one end of each wire connected to the radio and the other end hanging free in space  Dell Inspiron N3610 battery 5200mAh.
  • Since this is the simplest practical antenna, it is also used as a reference model for other antennas; gain with respect to a dipole is labeled as dBd. Generally, the dipole is considered to be omnidirectional in the plane perpendicular to the axis of the antenna, but it has deep nulls in the directions of the axis  Dell Inspiron N5010 battery 5200mAh.
  • Variations of the dipole include the folded dipole, the half wave antenna, the ground plane antenna, thewhip, and the J-pole.
  • The Yagi-Uda antenna is a directional variation of the dipole with parasitic elements added which are functionality similar to adding a reflector and lenses (directors) to focus a filament light bulbDell Inspiron N7010 battery 5200mAh.
  • The random wire antenna is simply a very long (at least one quarter wavelength ) wire with one end connected to the radio and the other in free space, arranged in any way most convenient for the space available. Folding will reduce effectiveness and make theoretical analysis extremely difficult  Dell Inspiron 1464 battery 5200mAh.
  • (The added length helps more than the folding typically hurts.) Typically, a random wire antenna will also require an antenna tuner, as it might have a random impedance that varies non-linearly with frequency.
  • The horn is used where high gain is needed, the wavelength is short (microwave) and space is not an issueDell Inspiron 1564 battery 5200mAh.
  • Horns can be narrow band or wide band, depending on their shape. A horn can be built for any frequency, but horns for lower frequencies are typically impractical. Horns are also frequently used as reference antennas.
  • The parabolic antenna consists of an active element at the focus of a parabolic reflector to reflect the waves into a plane waveDell Inspiron 1764 battery 5200mAh.
  • Like the horn it is used for high gain, microwave applications, such assatellite dishes.
  • The patch antenna consists mainly of a square conductor mounted over a groundplane. Another example of a planar antenna is the tapered slot antenna (TSA), as the Vivaldi-antenna  Dell Inspiron 1320 battery 5200mAh.

Practical antennas

Although any circuit can radiate if driven with a signal of high enough frequency, most practical antennas are specially designed to radiate efficiently at a particular frequency  Dell Inspiron 1320n battery 5200mAh.

An example of an inefficient antenna is the simple Hertzian dipole antenna, which radiates over wide range of frequencies and is useful for its small size. A more efficient variation of this is the half-wave dipole, which radiates with high efficiency when the signal wavelength is twice the electrical length of the antennaDell Vostro 1710 battery 5200mAh.

One of the goals of antenna design is to minimize the reactance of the device so that it appears as a resistive load. An "antenna inherent reactance" includes not only the distributed reactance of the active antenna but also the natural reactance due to its location and surroundingsDell Vostro 1720 battery 5200mAh

(as for example, the capacity relation inherent in the position of the active antenna relative to ground). Reactance diverts energy into the reactive field , which causes unwanted currents that heat the antenna and associated wiring, thereby wasting energy without contributing to the radiated output  Dell Studio XPS 1640 battery 5200mAh.

Reactance can be eliminated by operating the antenna at its resonant frequency, when its capacitive and inductive reactances are equal and opposite, resulting in a net zero reactive current. If this is not possible, compensating inductors or capacitors can instead be added to the antenna to cancel its reactance as far as the source is concernedDell Vostro A840 battery 5200mAh.

Once the reactance has been eliminated, what remains is a pure resistance, which is the sum of two parts: the ohmic resistance of the conductors, and theradiation resistance. Power absorbed by the ohmic resistance becomes waste heat, and that absorbed by the radiation resistance becomes radiated electromagnetic energyDell Vostro A860 battery 5200mAh.

The greater the ratio of radiation resistance to ohmic resistance, the more efficient the antenna.

Effect of ground

Antennas are typically used in an environment where other objects are present that may have an effect on their performance. Height above ground has a very significant effect on the radiation pattern of some antenna typesDell Studio 1535 battery 5200mAh/7800mAh.

At frequencies used in antennas, the ground behaves mainly as a dielectric . The conductivity of ground at these frequencies is negligible. When an electromagnetic wave arrives at the surface of an object, two waves are created: one enters the dielectric and the other is reflected  Dell Studio 1735 battery 5200mAh/7800mAh.

If the object is a conductor, the transmitted wave is negligible and the reflected wave has almost the same amplitude as the incident one. When the object is a dielectric, the fraction reflected depends (among others things) on the angle of incidence  Dell Vostro 1310 battery 5200mAh.

When the angle of incidence is small (that is, the wave arrives almost perpendicularly) most of the energy traverses the surface and very little is reflected. When the angle of incidence is near 90° (grazing incidence) almost all the wave is reflected  Dell Latitude E6400 battery,10400mAh/7800mAh .

Most of the electromagnetic waves emitted by an antenna to the ground below the antenna at moderate (say < 60°) angles of incidence enter the earth and are absorbed (lost). But waves emitted to the ground at grazing angles, far from the antenna, are almost totally reflectedDell Latitude E6400 Battery,10400mAh/7800mAh.

At grazing angles, the ground behaves as a mirror. Quality of reflection depends on the nature of the surface. When the irregularities of the surface are smaller than the wavelength reflection is good.

This means that the receptor "sees" the real antenna and, under the ground, the image of the antenna reflected by the groundDell Latitude E6400 Battery,10400mAh/7800mAh.

If the ground has irregularities, the image will appear fuzzy.

If the receiver is placed at some height above the ground, waves reflected by ground will travel a little longer distance to arrive to the receiver than direct waves. The distance will be the same only if the receiver is close to groundDell Latitude E6500 battery,10400mAh/7800mAh.

In the drawing at right, we have drawn the angle \scriptstyle{\theta}far bigger than in reality. Distance between the antenna and its image is \scriptstyle{d}.

The situation is a bit more complex because the reflection of electromagnetic waves depends on the polarization of the incident waveDell Latitude E6500 battery,10400mAh/7800mAh.

As the refractive index of the ground (average value \scriptstyle{\simeq 2}) is bigger than the refractive index of the air (\scriptstyle{\simeq 1}), the direction of the component of the electric field parallel to the ground inverses at the reflection. This is equivalent to a phase shift of \scriptstyle{\pi}radians or 180°Dell Latitude E6500 battery,10400mAh/7800mAh.

The vertical component of the electric field reflects without changing direction. This sign inversion of the parallel component and the non-inversion of the perpendicular component would also happen if the ground were a good electrical conductorDell Latitude E6500 battery,10400mAh/7800mAh.

This means that a receiving antenna "sees" the image antenna with the current in the same direction if the antenna is vertical or with the current inverted if the antenna is horizontalHP Pavilion DV6-1210SA battery - 5200mAh/8800mAh.

For a vertical polarized emission antenna the far electric field of the electromagnetic wave produced by the direct ray plus the reflected ray is:

\textstyle{\left|E_\perp\right|=2\left|E_{\theta_1}\right|\left|\cos\left({kd\over2}\sin\theta\right) \right|}

The sign inversion for the parallel field case just changes a cosine to a sineHP Pavilion DV7 battery - 7200mAh:

\textstyle{\left|E_=\right|=2\left|E_{\theta_1}\right| \left|\sin\left({kd\over2}\sin\theta\right) \right|}

In these two equations:

  • \scriptstyle{E_{\theta_1}}is the electrical field radiated by the antenna if there were no ground.
  • \scriptstyle{k={2\pi\over\lambda}}is the wave number  Ibm THINKPAD X200 Battery 8800mAh .
  • \scriptstyle{\lambda}is the wave length.
  • \scriptstyle{d}is the distance between antenna and its image (twice the height of the center of the antenna).

For emitting and receiving antenna situated near the ground (in a building or on a mast) far from each other, distances traveled by direct and reflected rays are nearly the same  Ibm THINKPAD X200 Battery 8800mAh .

There is no induced phase shift. If the emission is polarized vertically the two fields (direct and reflected) add and there is maximum of received signal. If the emission is polarized horizontally the two signals subtracts and the received signal is minimum. This is depicted in the image at right  Ibm THINKPAD X200 Battery 8800mAh .

In the case of vertical polarization, there is always a maximum at earth level (left pattern). For horizontal polarization, there is always a minimum at earth level. Note that in these drawings the ground is considered as a perfect mirror, even for low angles of incidence  SONY VAIO VGN-FW21E Battery.

In these drawings the distance between the antenna and its image is just a few wavelengths. For greater distances, the number of lobes increases.

Note that the situation is different–and more complex–if reflections in the ionosphere occur  Asus M52N Battery.

This happens over very long distances (thousands of kilometers). There is not a direct ray but several reflected rays that add with different phase shifts.

This is the reason why almost all public address radio emissions have vertical polarization  Dell Latitude E6400 ATG Battery.

As public users are near ground, horizontal polarized emissions would be poorly received. Observe household and automobile radio receivers. They all have vertical antennas or horizontal ferrite antennas for vertical polarized emissions  SONY VAIO VGN-FW21J Battery.

In cases where the receiving antenna must work in any position, as in mobile phones, the emitter and receivers in base stations use circular polarized electromagnetic waves.

Classical (analog) television emissions are an exception  SONY VAIO VGN-FW21L Battery.

They are almost always horizontally polarized, because the presence of buildings makes it unlikely that a good emitter antenna image will appear . However, these same buildings reflect the electromagnetic waves and can create ghost images. Using horizontal polarization  SONY VAIO VGN-FW21M Battery,

reflections are attenuated because of the low reflection of electromagnetic waves whose magnetic field is parallel to the dielectric surface near the Brewster's angle. Vertically polarized analog television has been used in some rural areas  SONY VAIO VGN-FW21Z Battery.

In digital terrestrial television reflections are less obtrusive, due to the inherent robustness of digital signalling and built-in error correction.

Mutual impedance and interaction between antennas

Current circulating in any antenna induces currents in all others  SONY VAIO VGN-FW25T/B Battery.

One can postulate a mutual impedance\scriptstyle{Z_{12}}between two antennas that has the same significance as the \scriptstyle{j\omega M}in ordinary coupled inductors. The mutual impedance \scriptstyle{Z_{12}}between two antennas is defined as:

Z_{12}={v_2\over i_1}

where \textstyle{i_{1}}is the current flowing in antenna 1 and \textstyle{v_2}is the voltage that would have to be applied to antenna 2–with antenna 1 removed–to produce the current in the antenna 2 that was produced by antenna 1  SONY VAIO VGN-FW26T/B Battery.

From this definition, the currents and voltages applied in a set of coupled antennas are:

\begin{matrix} v_1&=&i_1Z_{11}&+&i_2Z_{12}&+& \cdots &+& i_nZ_{1n}\\ v_2&=&i_1Z_{21}&+& i_2Z_{22}&+&\cdots&+&i_nZ_{2n} \\ \vdots & & \vdots & & \vdots & & & & \vdots \\ v_n&=&i_1Z_{n1}&+&i_2Z_{n2}&+&\cdots&+&i_nZ_{nn}\end{matrix}

where:  SONY VAIO VGN-FW27/B Battery

  • \scriptstyle{v_i}is the voltage applied to the antenna i
  • \scriptstyle{Z_{ii}}is the impedance of antenna i
  • \scriptstyle{Z_{ij}}is the mutual impedance between antennas iand j

Note that, as is the case for mutual inductances  SONY VAIO VGN-FW27/W Battery,

\scriptstyle{Z_{ij}\,= \,Z_{ji}}

This is a consequence of Lorentz reciprocity. If some of the elements are not fed (there is a short circuit instead a feeder cable), as is the case in television antennas (Yagi-Uda antennas), the corresponding \textstyle{v_i}are zero. Those elements are called parasitic elementsSONY VAIO VGN-FW31ZJ Battery.

Parasitic elements are unpowered elements that either reflect or absorb and reradiate RF energy.

In some geometrical settings, the mutual impedance between antennas can be zero. This is the case for crossed dipoles used in circular polarization antennas  SONY VAIO VGN-FW27T/H Battery.

The pentagrid converteris a radio receiving valve (vacuum tube) with five grids used as the frequency mixer stage of a superheterodyne radio receiver  SONY VAIO VGN-FW29/B Battery.

The pentagrid was part of a line of development of valves that were able to take an incoming RF signal and change its frequency to a fixed intermediate frequencywhich was then amplified, and detected in the remainder of the receiver circuitry. The device was generically referred to as a frequency changeror just mixer  SONY VAIO VGN-FW290JRB Battery.

Origins

The first devices designed to change frequency in the manner described above seem to have been developed by the French who simply put two grids into what would otherwise have been an ordinarytriode valve (the bi-grille)  SONY VAIO VGN-FW290JTB Battery.

Although technically a four electrode device, neither the term tetrode nor the tetrode valve as we know it today had yet appeared. Each grid was able to accept one of the incoming signals and the non-linearity of the device produced the sum and difference frequencies  SONY VAIO VGN-FW290JTH Battery.

The valve would have been very inefficient but, most importantly, the capacitive coupling between the two grids would have been very large. It would therefore have been quite impossible to prevent the signal from one grid coupling out of the other. At least one reference claims that the bi-grille was self oscillating, but this has not been confirmedSONY VAIO VGN-FW33G/E1 Battery.

When Edwin Armstrong invented the superheterodyne receiver in 1918, although the tetrode had been invented a couple of years earlier, he nevertheless employed only triodes in his design. Armstrong employed a pair of triodes as his mixer stage  SONY VAIO VGN-FW33G/W Battery.

One operated in a conventional oscillator circuit, but he was able to employ the other as a mixer by coupling the oscillator signal into the mixer's cathode, and the received signal to the grid. The sum and difference frequencies were then available in the mixer's anode (or plate) circuit  SONY VAIO VGN-FW33GW Battery.

Once again, the problem of coupling between the circuits would be ever present.

Shortly after Armstrong invented the superhet, a triode mixer stage design was developed that not only mixed the incoming signal with the local oscillator, but the same valve doubled as the oscillator  Dell XPS M1210 Batteryhttp://www.hdd-shop.co.uk.

This was known as the autodyne mixer. Early examples had difficulty oscillating across the frequency range because the oscillator feedback was via the first intermediate frequency transformer primary tuning capacitor which was too small to give good feedback. Also keeping the oscillator signal out of the antenna circuit was difficult  Dell KM958 battery.

The invention of the tetrode demonstrated the idea of screening electrodes from each other by using additional earthed (grounded) grids (at least as far as the signal was concerned). In 1926, Philips invented a technique of adding yet another grid to combat the secondary emission that the tetrode suffered from  Dell Studio 1555 battery.

All the ingredients for the pentagrid were now in place.

The Pentagrid

The development of the pentagrid or heptode valve was a novel development in the mixer story  Sony VGP-BPS13 battery.

The idea was to produce a single valve that not only mixed the oscillator signal and the received signal and produced its own oscillator signal at the same time but, importantly, did the mixing and the oscillating in different parts of the same valve  Sony VGP-BPS13/B battery.

The invention of the device at first sight doesn't seem to be obscure, but it would appear that it was developed in both America and the United Kingdom, more or less at the same time. However, the UK device is different to its American counterpart  Sony VGP-BPS13/S battery.

It is known that Donald G. Haines of RCA applied for a patent for the pentagrid on 28 March 1933 (subsequently granted on 29 March 1939) under US patent number 2,148,266. The pentagrid also featured in a UK patent (GB426802) granted on 10 April 1935  Sony VGP-BPS13A/B battery.

However, the Ferranti company of Great Britain entered the valve business with the first known UK produced pentagrid, the VHT4late in 1933 (though it must have been in development, and would certainly have existed as a prototype well before this time)  Sony VGP-BPS13B/B battery.

The pentagrid proved to be a much better mixer. Since the oscillator circuit was more or less self contained, good feedback for reliable oscillation across the frequency range was easy to obtain. Some manufacturers that had adopted the autodyne mixer converted some, if not all, of their designs to pentagrid mixers  Sony VGP-BPL9 battery.

What was the goal to develop a reliable self oscillating mixer? The reasons were to differ from the UK to America. The UK radio manufacturers had to pay a royalty of £1 per valve holder to the British Valve Association to cover use of their members' patent rights. Further  Sony VGP-BPS13B/B battery,

they dictated than not more than one electrode structure could be contained in a single envelope (which would have evaded the royalty - at least in part). The Americans appeared to be driven by the desire to produce a low cost 'every expense spared' design which was to lead to theAll American Five  Sony VGP-BPL15 battery.

By making the mixer self oscillate, the necessity of providing a separate oscillator valve is avoided. The All American Five was to use a pentagrid converter from when it first appeared in 1934, right up until valves became obsolete when transistors took over  Dell Inspiron E1505 battery.

In the UK, the five grids operated thus. Grid 1 acted as the oscillator grid in conjunction with grid 2 which acted as its anode. Grid 4 accepted the incoming signal with the remaining two grids, 3 and 5 connected together (usually internally) which acted as screen grids to screen the anode, grid 4 and grid 2 from each other  HP Pavilion dv6000 Battery.

Because grid 2 was a 'leaky' anode in that it allowed part of the modulated electron stream through, the oscillator was coupled into the mixing section of the valve. In fact, in some designs, grid 2 consisted of just the support rods, the actual grid wire itself being omitted  HP Pavilion dv8000 battery.

In America, the configuration was different. Grid 1 acted as the oscillator grid as before, but in this case, grids 2 and 4 were connected together (again usually internally). Grid 2 functioned as both a screen and the oscillator anode, in this case the grid wire had to be present to provide the screening  HP PAVILION DV6000 Battery,  8800mAh.

Grid 3 accepted the incoming signal. Grid 4 screened this from the anode, and grid 5 was a suppressor grid to suppress secondary emission. This configuration limited the oscillator design to one where the oscillator 'anode' was operated from the HT+ (B+) railHP PAVILION DV8000 Battery,  8800mAh.

This was often accomplished by using a Hartley Oscillator circuit and taking the cathode to the tap on the coil.

It will be noted that the UK version would have had significant secondary emission and would also have had a tetrode kink. This was exploited in providing the non linearity necessary to produce good sum and difference signals  SONY VAIO VGN-FZ Battery.

The American devices although having no secondary emission due to the suppressor grid, nevertheless were able to get the required non linearity by biasing the oscillator such that the valve was overdriven. The American version was also a little more sensitive because the grid that accepted the signal was closer to the cathode increasing the amplification factorHP Pavilion DV6000 battery - 8800mAh.

The pentagrid converter in either guise operated extremely well, but it suffered from the limitation that a strong signal was able to 'pull' the oscillator frequency away from a weaker signal. This was not considered a major problem in broadcast receivers where the signals were likely to be strong  HP Pavilion DV8000 battery - 7800mAh,

but it became a problem when trying to receive weak signals that were close to strong signals. Some short wave radios managed quite satisfactorily with these devices. Special high frequency versions appeared after World War II for the 100 MHz FM bands. Examples are the 6SB7Y(1946) and the 6BA7(1948)  HP Pavilion DV6000 battery - 8800mAh.

The pulling effect had a beneficial side effect in that it gave a degree of automatic tuning.

Another disadvantage was that in spite of the presence of the screen grids, the electron beam, modulated by the oscillator electrodes, still had to pass through the signal grid, and coupling of the oscillator into the signal circuit was inevitableHP Pavilion DV8000 battery - 6600mAh.

The American Federal Communication Commission (FCC) started requiring radio manufacturers to certify that their products avoided this interference under Part 15 of their rules. In the UK the Postmaster General (who was responsible for radio licensing), laid down a set of stringent rules concerning radio interference  SONY VAIO VGN-FZ18 Battery.

The Hexode

It may come as a surprise that the Hexode was actually developed after the heptode or pentagrid. It was developed in Germany as a mixer but was designed from the start to be used with a separate triode oscillator  SONY VAIO VGN-FZ21E Battery.

Thus the grid configuration was grid 1, signal input; grids 2 and 4 screen grids (connected together - again, usually internally) and grid 3 was the oscillator input. The device had no suppressor grid. A major advantage was that by using grid 1 as the signal input grid, the device was more sensitive to weak signals  SONY VAIO VGN-FW31J Battery 10400mAh.

It was not long before they put the triode and hexode structures in the same glass envelope - by no means a new idea. The triode grid was usually internally connected to the hexode grid 3, but this practice was dropped in later designs when the mixer section operated as a straight IF amplifier in AM/FM sets when operating on FMSONY VAIO VGN-FW31J Battery10400mAh,

the mixing being carried out in a dedicated FM frequency changing section.

The UK manufacturers were initially unable to use this type of mixer because of the BVA prohibition on multiple structures (and indeed separate valves because of the levy)  SONY VAIO VGN-FW21E Battery.

Indeed one UK company, MOV, successfully enforced the cartel rules against the German Lissen company in 1934 when they attempted to market a radio in the UK which had the triode-hexode mixer.

Following pressure from the UK manufacturers, the BVA were compelled to relax the rules and the UK started to adopt triode-hexode mixers  SONY VAIO VGN-NR11S/S Battery.

The Mullard ECH35was a popular choice.

One company, Osram made an ingenious move. One of their popular pentagrid converter designs was the MX40, initially marketed in 1934. They put on sale in 1936, the X41triode-hexode frequency changer  SONY VAIO VGN-NR11M/S Battery.

The clever bit was that the X41was a direct plug in pin compatible replacement for the MX40. Thus a pentagrid radio could be easily converted to a triode-hexode without any other circuit modifications  SONY VAIO VGN-NR11Z/S Battery.

It is interesting to note, that America never really adopted the triode-hexode and it was seldom used, even though the 6K8triode-hexode was available to manufacturers in 1938.

In some designs, a suppressor grid was added to produce yet another heptode design. Mullard's ECH81became popular with the move to miniature 9 pin valves  SONY VAIO VGN-NR11Z/T Battery .

The Octode

Although not strictly a pentagrid (in that it does not have 5 grids), this device nevertheless operates on the pentagrid principle. It resulted simply from the addition of a suppressor grid to the UK version of the pentagrid heptode  Sony VAIO VGN-FZ21E Battery.

This was done mainly to reduce the power consumption for use in radio sets operated by dry batteries that were becoming increasingly popular.

In North America, the only octode manufactured was the 7A8  Sony VAIO VGN-FW21E Battery.

Introduced by Sylvania in 1939 (and used mostly by Philco), this valve was the product of adding a suppressor grid to type 7B8, which was the loctal version of type 6A7. Adding the suppressor allowed Sylvania to lower the current of the 6.3 volt heater from 300 milliamperes to 150 milliamperes while maintaining the same conversiontransconductanceSony VAIO VGN-NR11S/S Battery

(550 microsiemens). This allowed Philco to use this valve in every line of radio throughout the 1940s.

One octode design worthy of mention was the Philips EK3Octode. This was designated as a 'beam octode'. The novel part about the design was that grids 2 and 3 were constructed as beam forming plates  Sony VAIO VGN-NR11Z/S Battery.

This was done in such a way that Philips claimed that the oscillator electron beam and the mixer electron beams were separated as much as possible and thus the pulling effect was minimised. No information is available as to the degree of success  Sony VAIO VGN-NR11M/S Battery.

The Pentode

The use of a pentode would seem an unlikely choice for a frequency converter. However, during the Great Depression, many American radio manufacturers used pentode types 6C6, 6D6, 77and 78in their lowest priced AC/DC receivers because they were cheaper than pentagrid type 6A7 Sony VAIO VGN-NR11Z/T Battery .

In these circuits, the suppressor (grid 3) acted as the oscillator grid.

One UK company, Mazda, produced a triode-pentode frequency changer, the AC/TP. Designed for low cost AC radios, the device was deliberately designed to allow strong signals to pull the oscillator without the risk of radiating the oscillator signal from the aerial. The cathode was common to both sections of the valve  SONY VAIO VGN-FZ180E Battery.

The cathode was connected to a secondary coil on the oscillator coil and thus coupled the oscillator into the pentode mixer section, the signal being applied to grid 1 in the conventional manner. The AC/TP was one of the AC/ range of valves designed for low cost radios  SONY VAIO VGN-FZ220E Battery.

They were considered durable for their time (even the AC/TP frequency changer, which was normally problematic). Any AC/ valves encountered today are likely to be brand new as service shops stocked up on spares which were seldom required  SONY VAIO VGN-FZ340E Battery.

Nomenclature

In order to distinguish between the two versions of the heptode or pentagrid, manufacturers data often describes them as 'heptode of the Hexode type' for a heptode without a screen grid, and a 'heptode of the octode type', where a screen grid is present  SONY VAIO VGN-FZ430E Battery.

The term All American Fiveis a colloquial name for mass-produced, superheterodyne radio receivers that used five vacuum tubes in their design. These radio sets were designed to receive amplitude modulation (AM) broadcasts in the medium wave band, and were manufactured in the United States from the mid 1930s until the early 1960s  SONY VAIO VGN-FZ460E Battery.

By eliminating a power transformer, cost of the units was kept low; the same principle was later applied to television receivers. Variations in the design for lower cost, shortwave bands, better performance or special power supplies existed, although many sets used an identical set of vacuum tubes  SONY VAIO VGN-FZ480E Battery.

The radio was called the "All American Five" because the design represented the majority of radios manufactured for home use in the USA and Canada in the tube era. They were manufactured in the millions by hundreds of manufacturers from the 1930s onward, with the last examples being Japanese-made units  SONY VAIO VGN-FZ4000 Battery.

Fewer examples were used in Europe as the 220 volt mains supply meant extra work for designers in providing tube heater voltage. AA5 designs were also called AC/DC receivers because they could operate on DC (which was still in use in several areas of the USA when the design was developed) as well as AC, though this was incidental to the design objective  SONY VAIO VGN-FZ31E Battery.

When operated on DC, they would only work if the plug was inserted with the correct polarity. Also, if run from a DC supply the radio had a reduced performance because the B+ voltage would only be 120 volts compared with 160-170 volts when operated from ACSONY VAIO VGN-FZ31B Battery.

The philosophy behind the design was simple: it had to be as cost-effective to make as possible. The design was optimized to provide good performance for the price. At least one radio manufacturer, Arthur Atwater Kent, preferred to go out of business rather than attempt to compete with 'midget' or low-cost AA5 designs  SONY VAIO VGN-FZ31J Battery.

Many design tricks were used to reduce production costs of the five-tube radio. The heaters of the vacuum tubes were all rated to use the same current, so they could be operated in series from line voltage. The more-powerful tubes (the rectifier and audio output tube) required more-powerful heaters that dropped proportionally more of the line voltage  SONY VAIO VGN-FZ31M Battery.

The rectifier tube had a tap on the heater to power a dial light. The plate current was routed through that portion of the rectifier heater, in order to make up for the current diverted to the dial lamp. If the dial lamp failed, that part of the rectifier heater would have a larger current which could burn out the tube in a few months  SONY VAIO VGN-FZ31Z Battery.

Early radios had a resistor network to minimize the problem but this was soon eliminated once manufacturers figured out that the cost of replacing the tube was not their problem. As with Christmas tree lights, if one tube heater failed, none of the tube heaters would operate  SONY VAIO VGN-FZ38M Battery.

When the detector/first audio tube contained a second diode, it could be used to provide automatic gain control (AGC), or AGC bias could be derived from the audio detector diode.

The radio used a half wave rectifier to produce about 160-170 volts of plate voltage  SONY VGP-BPS8 Battery.

This simple rectifier coupled with the wiring of the heaters in series eliminated the mains transformer.

The frequency mixer was of the pentagrid converter design to save the cost of a separate oscillator tube. The detector and first audio stage were provided by a dual Diode/Triode combination tube  SONY VGP-BPS13/S Battery.

Potential hazards of the design

Many early examples of the 'All-American Five' posed a shock hazard to their owners. Lacking a mains transformer, the chassis of the AA5 radio was directly connected to one side of the mains electric supply  SONY VGP-BPS13A/B Battery

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The hazard was made worse because the on/off switch was often in the wire of the mains supply which was connected to the chassis, meaning that the chassis could be "hot" when the set was either 'on' or 'off' - depending on which way the plug was inserted in the power outlet  SONY VGP-BPS13B/B Battery.

The metal chassis securing screws were often accessible from the outside of the Bakelite or wood case, and there were many examples of owners receiving a shock by making contact with these screws while handling a set.

After public outcry and several sensational press accounts of the problem, the hazard was eliminated from later sets by the use of an internal ground bus connected to the chassis by an isolation network  SONY VGP-BPS13A/S Battery.

Underwriters Laboratories required the adoption of the floating chassis, as isolation from the mains (the exact circuit and component values were not specified although the leakage current allowed was specified) to limit the shock to a "safe" current levelSONY VGP-BPS13AS Battery.

The chassis was maintained at RF ground (for shielding) by a bypass capacitor (typically 0.05 µF to 0.2 µF) usually with a resistor connected across it (typically 220 k? to 470 k? , although values as small as 22 k? were sometimes used or the resistor was simply omitted)  Dell Inspiron 1320n Battery.

See here for a typical schematic of a 1948 model AC/DC radio with a 220K isolation resistor.

Over the years, these paper capacitors often become leaky, and may allow sufficient current flow to give the user a shock  Dell Studio 1450 Battery.

Variations on the theme

Although four-, six-, and even a few rare eight-tube radios were also produced, they were not common. The four-tube version was of inferior performance, as they might have had no IF amplifier tube, although some designs used a selenium rectifier in place of the rectifier tube  Dell Studio 1457 Battery.

The six-tube versions added either a RF amplifier tube, a push-pull audio power amplifier tube, or a beat frequency oscillatortube (to allow one to listen to Morse code or single-sideband modulation). However, these radios cost sufficiently more that they did not sell well  Dell Latitude D610 Battery.

The eight-tube versions cost even more, adding two or more of the features of the six-tube versions and sometimes an extra IF amplifier tube.

The original

The basic design of the 'All-American Five' had its origins in low-cost sets produced in the early days of radio   Toshiba NB100 Battery.

The very first set of metal tubes produced included 6-volt heater tubes that could be used to make a transformer-powered 6-tube radio. RCA released their first set of metal octal tubes for this design in 1939. The original design used the following tubes  Toshiba Satellite M65 battery:

  • Converter: 12A8
  • IF amplifier: 12K7
  • Detector and first audio amplifier: 12Q7
  • Audio power output: 50L6
  • Rectifier: 35Z4.  Toshiba Satellite M60 battery

This series had the grids brought out as top caps on the signal tubes, and the 35Z4 did not have a provision for a dial light.

The most popular

The tube array in the early days of the Octal tubes was  Dell Latitude D830 Battery :

  • Converter: 12SA7
  • IF amplifier: 12SK7
  • Detector and first audio amplifier: 12SQ7
  • Audio power output: 50L6  Dell Latitude D620 Battery
  • Rectifier: 35Z5

These sets were first marketed in late 1939. Canadian sets would sometimes use a 35L6 in place of the 50L6, as parts of Canada used 110 volts as a design standard. Because areas near Niagara Falls had 25 Hz power, some Canadian sets had slightly larger filter capacitors  Dell Inspiron Mini 10 Battery.

The "Loctal" variant

The tube line up of the Loctal tubes was:

  • Converter: 14Q7
  • IF amplifier: 14A7
  • Detector and first audio amplifier: 14B6
  • Audio power output: 50A5  Sony VGN-FW11S Battery
  • Rectifier: 35Y4 or 35Z3

The redesign using miniature tubes

After the Second World War the set was redesigned to use miniature 7-pin tubes and the line up became:

  • Converter: 12BE6
  • IF amplifier: 12BA6  Sony VGN-FW11M Battery
  • Detector and first audio amplifier: 12AV6 or 12AT6
  • Audio power output: 50C5 or the less-common 50B5
  • Rectifier: 35W4

The 50C5 was introduced in 1948, to address concerns that the set might pose more of a shock hazard to the user if the 35W4 and 50B5 were to be accidentally interchanged  Sony VGN-FW139E/H battery.

The 50C5 is a 50B5 with a different pin-out.

In the postwar period, some makers built sets with a mixture of miniature and octal tubes.

The "Power-Saver" version  Dell Latitude E5400 Battery

Another low-power variation changed the tube heaters to run on 100 milliamperes rather than 150 milliamperes. Unfortunately the lower power also resulted in a slightly longer warm-up time:

  • Converter: 18FX6
  • IF amplifier: 18FW6  Dell Latitude E4200 Battery
  • Detector and first audio amplifier: 18FY6
  • Audio power output: 32ET5 or 34GD5
  • Rectifier: 36AM3

The voltage distribution has changed around the tube heaters but the total is still a little more than the 120 volt mains supply. This line-up is for an Admiral radio  Dell Inspiron 300M Battery.

Farm radio

A "farm radio" modification (usually done at the point of sale) allowed an AA5 to run off 32 volt DC, commonly generated by farm windmills. With a relatively simple rewiring, the tube heaters could be put in series-parallel to run off 32 volts – the three twelve-volt heaters in series and a 25L6, 35L6 or 43 in parallel  Dell Studio 1737 battery.

The tubes would still function with the heater voltage somewhat out of specifications. If run from a 32 volt supply the radio had a substantially reduced performance because the B+ voltage would only be 32 volts compared with 160-170 volts when operated from AC. With 32 volts on the plate, the radio tended to be insensitive  Dell Inspiron E1505 battery.

Sometimes only the tube heater power was derived from a windmill, and dry batteries were retained for the plate voltage supply. The advantage was that the heaters were a high and continuous load on the battery, whereas the plate voltage battery drain was smaller and intermittent  Dell RM791 battery.

Often a wet-cell rechargeable battery was used for tube heaters, recharged by a local garage or by exchanging with a vehicle battery.

Many 32 volt farm radios were factory-built for the purpose. They usually had two type 48 power tetrodes that could operate with B+ voltages as low as 28 volts  Toshiba Satellite P10 Battery.

The type 48 pairs were parallel connected, or connected in push-pull as shown in this schematic of a 1936 farm radio from Sears Roebuck. Some factory 32-volt radios used an electromechanical vibrator power supply to provide increased voltage  Acer Aspire One battery 10400mAh .

Vibrator power supplies could also be made to work from a 6 volt supply from a dedicated wind-charger or from a car battery borrowed from a farm vehicle.

Battery operated variants

A number of other versions of the set appeared, including some that did have a transformerSONY VGN-FZ210CE Battery,

a version that operated in a motor vehicle off a 6-volt supply and even a version that operated from either dry batteries or the mains supply. The battery version commonly used tubes where the filament was heated by a single 1.5-volt dry cell and plate voltage was supplied by a (nominally) 90-volt battery  Dell Precision M70 Battery.

One version, called a Three-way portablebecause it could be operated any of three ways: batteries, the AC line, or the DC line; typically had the following tube array:

  • Converter: 1R5
  • IF amplifier: 1U4    Toshiba Satellite L305 Battery
  • Detector and first audio amplifier: 1U5
  • Audio power output: 3V4
  • Rectifier: 35W4, 117Z3, or a selenium rectifier

This version used a 7.5 V A battery and a 90 V B battery  Toshiba Satellite T4900 Battery.

Note that the A battery did not need to heat the rectifier tube because, when operating from the batteries, the rectifier was not needed.

When operating on batteries, this version had almost instant warmup because of the tubes used their filaments as cathodes  Toshiba PA3399U-2BRS battery.

This setup was common on Motorola portable radios commonly resembling metal "lunch boxes".

Variations

Since the AA5 was a minimalist design, there was plenty of room for enhanced versions, resulting in an "AA6"Sony VGP-BPS10 battery 10400mAh:

  • A few sets added an extra 12SK7 as an RF or IF amplifier. This would require using a 35L6 to maintain the heater voltage.
  • Or, another audio amplifier tube could be added for increased audio output. To keep the total heater voltage at around 120 V, the two output tubes would have to be 25 to 35-volt types, such as the 35L6 or 25L6Sony VGP-BPS9 battery 10400mAh.

There were even a few "AA4" designs, usually midget sets, only usable in strong-signal metropolitan areas, because most had no IF amplifier (although some replaced the rectifier tube with a selenium rectifier).

To reduce costs further sometimes a pair of 12AU6 pentodes was used, one as an autodyne converter (instead of a pentagrid converter) and the other as an audio preamplifier  Sony VGP-BPS11 battery 10400mAh.

Series string order

According to various editions of the RCA Receiving Tube Manual, the heater string of an AC/DC radio should be arranged in a particular order to minimize hum. Assuming that all functions are performed by separate tubes, the heaters in the string should be arranged as follows  Sony VGP-BPS22 battery 10400mAh:

  1. Input stage
  2. Ballast tube or resistor
  3. Rectifier
  4. Audio power output amplifier
  5. RF and IF amplifiers
  6. Converter  Sony VGP-BPL8 battery  10400mAh
  7. First AF amplifier
  8. Detector
  9. Ground/B-minus line

Not all manufacturers followed this recommendation  Sony VGP-BPS14 battery 10400mAh .

Effect on television design

Many black-and-white and color television receivers were built using All American Five principles, including a hot chassis and series-wired heaters. The designs were found primarily in portable or inexpensive sets ranging from the 1950s to even as late as the GE Portacolor series which was finally discontinued in the 1980s  Sony VGP-BPS21 battery   10400mAh.

Early sets tended to use selenium rectifiers in place of a tube; later sets used silicon diodes. Some of these sets were hybrid, using transistors for small signal applications and vacuum tubes in place of then-expensive power transistors. Some also included a rectifier diode in series with the tube filaments; when the set was off  Toshiba Satellite A200 Battery,

the rectifier kept the filaments partially heated—these sets were often sold as "Instant On" or "Insta-Play" or any number of similar variations.

Servicing precautions

Since the chassis of the set may be connected directly to the live side of the power line, service shops used an isolation transformer to protect technicians from a shock hazard  Toshiba Satellite 1200 Battery.

Some restorers will rewire the hot chassis set to put the chassis at neutral at all times. Some TV designs only require polarizing the plug, while others require rewiring the power supply to remove the switch from chassis ground. Power outlets must be wired properly for this modification to work  Toshiba Satellite M300 Battery.

The Utility Radiowas an all-mains 4-valve domestic superhet radio receiver, manufactured in Great Britain during the 1939–45 World War.

When war broke out in 1939 all the British radio manufacturers switched to producing a wide range of military radio equipment for the armed forces  SONY VGP-BPS13A/Q Battery.

Perhaps the most famous product was the R1155communications receiver used by the RAF. After a few years there was a shortage of radio repairmen as they had all been called up to maintain vital radio and radar equipment. Similarly there was a shortage of spare parts, particularly valves, as all production was for the services  SONY VGP-BPS13A/Q Battery.

This meant it was very difficult to get a radio repaired and with no new sets available there was a desperate need to overcome the problem.

The Government solved this by arranging for all radio manufacturers to produce a standard design with as few components as possible  SONY VGP-BPS13B/Q Battery.

Earlier the Government had introduced the 'Utility' brand to ensure that all clothing, which was rationed, was produced to a reasonable quality standard as prior to its introduction a lot of shoddy goods had appeared on the market. So the 'Utility' brand was adopted for this wartime radio  SONY VGP-BPS13B/Q Battery.

The only significant shortcoming compared with pre-war radios was the absence of a long wave band and a simple tuning dial. This resulted in fewer tuning circuits and the absence of a wave-change switch. The tuning dial was a very crude affair compared with pre-war when the tuning dial was a work of art displaying dozens of stations throughout Europe  SONY VGP-BPS13/Q Battery.

Dials were marked in metres with only the 'Home' and 'Forces' stations identified.

The sets used a four-valve superhet circuit with an audio output of 4 watts at 10% total harmonic distortion; they performed as well as many pre-war sets  SONY VGP-BPS13/Q Battery.

The valve complement consisted of a triode-hexode frequency changer, a variable-? RF pentode IF amplifier and a high slope output pentode. A copper oxide diode was used for demodulation and the HT line was derived from a full wave rectifier. All valves were on International Octal sockets apart from the rectifier which was on a British 4-pin base  SONY VGP-BPS21A/B Battery.

There were minor variations between set makers; for instance Philips used IF transformers with adjustable ferrite cores (so-called slug tuning) rather than the conventional trimmer capacitors.

The general public were unable to tell the manufacturer of a particular set although each manufacturer used a code to identify themselves to dealers  SONY VGP-BPS21/S Battery.

For some curious reason the valves carried cryptic designations such as 274. They were produced by valve makers such as Mullard, MOV, Cossor, Mazda and Brimar. Dealers, knowing the maker of a set and which valve manufacturer that maker used, could easily deduce which pre-war types these were  SONY VGP-BPS21B Battery.

The set could be seen as the British equivalent of the German Peoples' Receiver (Volksempfänger). The external links below show that 44 different manufacturers produced the 'Utility' set, today only two brands remain: Roberts Radio and Bush RadioSONY VGP-BPS21A Battery.

The Volksempfänger(German for "people's receiver") was a range of radio receivers developed by Otto Griessing at the request of Joseph Goebbels.

The purpose of the Volksempfänger-program was to make radio reception technology affordable to the general publicSONY VGP-BPS21 Battery.

Joseph Goebbels realized the great propaganda potential of this relatively new medium and thus considered widespread availability of receivers highly important.

History

The original Volksempfänger VE-301 model was presented on August 18, 1933 at the Internationale Funkausstellung BerlinSony VGP-BPS21A/B Battery.

The VE-301 was available at a readily affordable price of 76 German Reichsmark (equivalent to two weeks' average salary), and a cheaper 35 Reichsmark model, the DKE38 (sometimes called Goebbels-Schnauze– "Goebbels' snout" – by the general public), was also later producedSony VGP-BPS21/S Battery,

along with a series of other models under the Volksempfänger, Gemeinschaftsempfänger, KdF (Kraft durch Freude), DKE (Deutscher Kleinempfänger) and other brands.

All Volksempfängerssold on the domestic market were purposely designed only to receive the Deutschlandsender and regionalSony VGP-BPS21A Battery

stations of the Reichs-Rundfunk-Gesellschaft, so as to ensure that Nazi propaganda broadcasts could readily be heard while other media, such as the BBC's European Service (now the World Service), could not. To this end most Volksempfängerslacked shortwave bands and didn't follow the practiceSony VGP-BPS21 Battery ,

common at the time among other receiver manufacturers, of marking the approximate dial positions of major European stations on its tuning scale. Generally only German (and later Austrian) stations were marked and cheaper models didn't have a proper scale at all (an example pictured above has its dial marked in arbitrary numbers rather thanmetres or kilocycles)Sony Vaio PCG-5G2L Battery.

The sensitivity was lower than a normal radio although in practice it could with some difficulty still be used to receive foreign stations (including the BBC)[2]particularly as these stations increased their transmission power during the war  Sony Vaio PCG-5G3L Battery.

Listening to foreign stations became a criminal offence in Nazi Germany when the war began, while in some occupied territories, such as Poland, allradio listening by non-German citizens was outlawed (later in this war this prohibition was extended to most other occupied countries coupled with mass seizures of radio sets )Sony Vaio PCG-5J1L Battery.

Penalties ranged from confiscation of radios and imprisonment to, particularly later in the war, the death penalty. Nevertheless, such clandestine listening was widespread in many Nazi-occupied countries and (particularly later in the war) in Germany itself. The Nazis also attempted radio jamming of some enemy stations with limited successSony Vaio PCG-5K2L Battery.

Effects

Much has been said about the efficiency of the Volksempfängeras a propaganda tool. Most famously, Hitler's architect and Minister for Armaments and War Production, Albert Speer, said in his final speech at the Nuremberg trialsSony Vaio PCG-5J2L Battery:

Hitler's dictatorship differed in one fundamental point from all its predecessors in history. His was the first dictatorship [...] which made the complete use of all technical means for domination of its own country. Through technical devices like the radio and loudspeaker, 80 million people were deprived of independent thought. It was thereby possible to subject them to the will of one man.Sony Vaio PCG-5K1L Battery

Utility receiver

The British equivalent of the Volksempfänger was the Utility Radio which was produced to a standard government approved design by a consortium of manufacturers using standard components to make repair easierSony Vaio PCG-6S2L Battery.

However, the primary purpose of the British design was to economise on the use of scarce materials and simplify repairs rather than to frustrate attempts at listening to foreign stations. (Such listening was officially discouraged but not actually forbidden in the United Kingdom)Sony Vaio PCG-6S3L Battery.

The Volksempfänger in popular culture

  • The album Radio-Activity, released in 1975, by German electronic music pioneers Kraftwerk prominently features a Volksempfänger, of the DKE brand (model 38), on its coverSony Vaio PCG-6V1L Battery.
  • German band Welle: Erdball has also produced a song entitled Volksempfänger VE-301, which first appeared on their Die Wunderwelt der Technikalbum of 2002  Sony Vaio PCG-6W1L Battery.

Censorshipis the suppression of speech or other communication which may be considered objectionable, harmful, sensitive, or inconvenient to the general body of people as determined by a government, media outlet, or other controlling bodySony Vaio PCG-6W2L Battery.

The rationale for censorship is different for various types of information censored:

  • Moral censorshipis the removal of materials that are obscene or otherwise considered morally questionable  Sony Vaio PCG-6W3L Battery.
  • Pornography, for example, is often censored under this rationale, especially child pornography, which is illegal and censored in many jurisdictions in the world.
  • Military censorshipis the process of keeping military intelligence and tactics confidential and away from the enemySony Vaio PCG-7111L Battery.
  • This is used to counter espionage, which is the process of gleaning military information. Very often, militaries will also attempt to suppress politically inconvenient information even if that information has no actual intelligence or combat-tactical valueSony Vaio PCG-7112L Battery.
  • Political censorshipoccurs when governments hold back information from their citizens. This is often done to exert control over the populace and prevent free expression that might foment rebellion.
  • Religious censorshipis the means by which any material considered objectionable by a certain faith is removedSony Vaio PCG-7113L Battery.
  • This often involves a dominant religion forcing limitations on less prevalent ones. Alternatively, one religion may shun the works of another when they believe the content is not appropriate for their faithSony Vaio PCG-7133L Battery.
  • Corporate censorshipis the process by which editors in corporate media outlets intervene to disrupt the publishing of information that portrays their business or business partners in a negative light, or intervene to prevent alternate offers from reaching public exposure  Sony Vaio PCG-7Z2L Battery.

Strict censorship existed in the Eastern Bloc. Throughout the bloc, the various ministries of culture held a tight rein on their writers.Cultural products there reflected the propaganda needs of the state. Party-approved censors exercised strict control in the early years  Sony Vaio PCG-8Y1L Battery.

In the Stalinist period, even the weather forecasts were changed if they had the temerity to suggest that the sun might not shine on May Day. Under Nicolae Ceau?escu in Romania, weather reports were doctored so that the temperatures were not seen to rise above or fall below the levels which dictated that work must stop  Sony Vaio PCG-8Y2L Battery.

Independent journalism did not exist in the Soviet Union until Mikhail Gorbachev became its leader; all reporting was directed by the Communist Party or related organizations. Pravda, the predominant newspaper in the Soviet Union, had a monopoly  Sony Vaio PCG-8Z1L Battery.

Foreign newspapers were available only if they were published byCommunist Parties sympathetic to the Soviet Union.

Possession and use of copying machines was tightly controlled in order to hinder production and distribution of samizdat, illegal self-published books and magazines  Sony Vaio PCG-8Z2L Battery.

Possession of even a single samizdat manuscript such as a book by Andrei Sinyavsky was a serious crime which might involve a visit from the KGB. Another outlet for works which did not find favor with the authorities was publishing abroad      SONY VAIO VGN-FW31J Battery.

The People's Republic of China, which continues Communist rule in politics, if not in the controlled economy, employs some 30,000 'Internet police'  to monitor the internet and popular search engines such as Google and Yahoo.

Iraq under Baathist Saddam Hussein had much the same techniques of press censorship as did Romania under Nicolae Ceau?escu but with greater potential violence  SONY VAIO VGN-FW31E Battery.

Cuban media is operated under the supervision of the Communist Party'sDepartment of Revolutionary Orientation, which "develops and coordinates propaganda strategies". Connection to the Internet is restricted and censored.

Censorship also takes place in capitalist nations, such as Uruguay  SONY VAIO VGN-FW31B Battery.

In 1973, a military coup took power in Uruguay, and the State practiced censorship. For example, writer Eduardo Galeano was imprisoned and later was forced to flee. His book Open Veins of Latin America was banned by the right-wing military government, not only in Uruguay, but also in Chile and Argentina  SONY VAIO VGN-FW31M Battery.

Critics of the Campaign finance reform in the United States claim that this reform imposes widespread restrictions on political speech.

State secrets and prevention of attention

In wartime, explicit censorship is carried out with the intent of preventing the release of information that might be useful to an enemy  SONY VAIO VGN-FW31Z Battery.

Typically it involves keeping times or locations secret, or delaying the release of information (e.g., an operational objective) until it is of no possible use to enemy forces. The moral issues here are often seen as somewhat different, as the proponents of this form of censorship argues that release of tactical information usually presents a greater risk of casualties among one's own forces and could possibly lead to loss of the overall conflict  SONY VAIO VGN-FW38M Battery.

During World War I letters written by British soldiers would have to go through censorship. This consisted of officers going through letters with a black marker and crossing out anything which might compromise operational secrecy before the letter was sent  SONY VAIO VGN-AW41JF Battery.

The World War II catchphrase "Loose lips sink ships" was used as a common justification to exercise official wartime censorship and encourage individual restraint when sharing potentially sensitive informationSONY VAIO VGN-AW41JF/H Battery.

An example of "sanitization" policies comes from the USSR under Joseph Stalin, where publicly used photographs were often altered to remove people whom Stalin had condemned to execution. Though past photographs may have been remembered or kept  SONY VAIO VGN-AW41MF Battery,

this deliberate and systematic alteration to all of history in the public mind is seen as one of the central themes of Stalinism  and totalitarianism.

Censorship is occasionally carried out to aid authorities or to protect an individual, as with some kidnappings when attention and media coverage of the victim can sometimes be seen as unhelpful  SONY VAIO VGN-AW41MF/H Battery.

Educational sources

The content of school textbooks is often the issue of debate, since their target audience is young people, and the term "whitewashing" is the one commonly used to refer to removal of critical or conflicting events  SONY VAIO VGN-FW30B Battery.

The reporting of military atrocities in history is extremely controversial, as in the case of The Holocaust (or Holocaust denial), Bombing of Dresden, the Nanking Massacre as found with Japanese history textbook controversies, the Armenian Genocide, the Tiananmen Square protests of 1989, and the Winter Soldier Investigation of the Vietnam WarSONY VAIO VGN-FW50B Battery.

In the context of secondary school education, the way facts and history are presented greatly influences the interpretation of contemporary thought, opinion and socialization. One argument for censoring the type of information disseminated is based on the inappropriate quality of such material for the young  SONY VAIO VGN-FW51B/W Battery.

The use of the "inappropriate" distinction is in itself controversial, as it changed heavily. A Ballantine Books version of the book Fahrenheit 451 which is the version used by most school classes contained approximately 75 separate edits, omissions, and changes from the original Bradbury manuscript  SONY VAIO VGN-FW51MF Battery.

Music and popular culture

Music censorship has been implemented by states, religions, educational systems, families, retailers and lobbying groups – and in most cases they violate international conventions of human rights  SONY VAIO VGN-FW51MF/H Battery.

Aside from the usual justifications of pornography, language and violence, some movies are censored due to changing racial attitudes or political correctness in order to avoid ethnic stereotyping and/or ethnic offense despite its historical or artistic valueSONY VAIO VGN-FW51ZF Battery .

One example is the still withdrawn "Censored Eleven" series of animated cartoons, which may have been innocent then, but are "incorrect" now.

Copy, picture, and writer approval

Copy approval is the right to read and amend an article, usually an interview, before publication  SONY VAIO VGN-FW51ZF/H Battery.

Many publications refuse to give copy approval but it is increasingly becoming common practice when dealing with publicity anxious celebrities. Picture approval is the right given to an individual to choose which photos will be published and which will not. Robert Redford is well known for insisting upon picture approval  SONY VAIO VGN-FW52JB Battery.

Writer approval is when writers are chosen based on whether they will write flattering articles or not. Hollywood publicist Pat Kingsley is known for banning certain writers who wrote undesirably about one of her clients from interviewing any of her other clients  SONY VAIO VGN-FW54FB Battery.

Maps

Censorship of maps is often employed for military purposes. For example, the technique was used in former East Germany, especially for the areas near the border to West Germany in order to make attempts of defection more difficult  SONY VAIO VGN-FW70DB Battery.

Censorship of maps is also applied by Google maps, where certain areas are grayed out or areas are purposely left out-dated with old imagery.

Meta-censorship

In this form of censorship, any information about existence of censorship and the legal basis of the censorship is censored, rules of censoring are classified, and removed texts or phrases are not marked  SONY VAIO VGN-FW71DB/W Battery.

Creative censorship

In this form of censorship, censors rewrite texts, giving these texts secret co-authors. This form of censorship is used in the novel Nineteen Eighty-Four  SONY VAIO VGN-FW72JGB Battery .

Internet

Internet censorship is control or suppression of the publishing or accessing of information on the Internet. The legal issues are similar to offline censorship  SONY VAIO VGN-FW73JGB Battery.

One difference is that national borders are more permeable online: residents of a country that bans certain information can find it on websites hosted outside the country. A government can try to prevent its citizens from viewing these even if it has no control over the websites themselves  SONY VAIO VGN-FW74FB Battery.

Barring total control on Internet-connected computers, such as in North Korea and Cuba, total censorship of information on the Internet is very difficult (or impossible) to achieve due to the underlying distributed technology of the Internet  SONY VAIO VGN-FW81HS Battery.

Pseudonymity and data havens (such as Freenet) allow unconditional free speech, as the technology guarantees that material cannot be removed and the author of any information is impossible to link to a physical identity or organization.

In some cases, Internet censorship may involve deceit  SONY VAIO VGN-FW81NS Battery.

In such cases the censoring authority may block content while leading the public to believe that censorship has not been applied. This may be done by having the ISP provide a fake "Not Found" error message upon the request of an Internet page that is actually found but blocked (see 404 error for details)  SONY VAIO VGN-FW81S Battery.

In November 2007, "Father of the Internet" Vint Cerf stated that he sees government control of the Internet failing due to private ownership.

The Australian government announced in December 2009 that it will introduce internet censorship legislation before the next Australian federal election  SONY VAIO VGN-FW82DS Battery.

Implementation

The former Soviet Union maintained a particularly extensive program of state-imposed censorship. The main organ for official censorship in the Soviet Union was the Chief Agency for Protection of Military and State Secretsgenerally known as the Glavlit, its Russian acronym  SONY VAIO VGN-FW82JS Battery.

The Glavlithandled censorship matters arising from domestic writings of just about any kind—even beer and vodka labels. Glavlitcensorship personnel were present in every large Soviet publishing house or newspaper  SONY VAIO VGN-FW82XS Battery;

the agency employed some 70,000 censors to review information before it was disseminated by publishing houses, editorial offices, and broadcasting studios. No mass medium escaped Glavlit's control. All press agencies and radio and television stations had Glavlitrepresentatives on their editorial staffs  SONY VAIO VGN-FW83DS Battery.

Sometimes, a specific and unique information whose very existence is barely known to the public, is kept in a subtle, near-censorship situation, being regarded as "subversive" or "inconvenient". Michel Foucault's 1978 text "Sexual Morality and the Law" (later republished as "The Danger of Child Sexuality")  SONY VAIO VGN-FW83JS Battery,

for instance - originally published as La loi de la pudeur[literally, "the law of decency"], defends the decriminalization of statutory rape and the abolition of age of consent laws.

When a publisher comes under pressure to suppress a book  SONY VAIO VGN-FW83XS Battery,

but has already entered into a contract with the author, they will sometimes effectively censor the book by deliberately ordering a small print run and making minimal, if any, attempts to publicize it. This practice became known in the early 2000s as privishingSONY VAIO VGN-FW90NS Battery .

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