HF-Relay - A New Shortwave System

The article below from Wireless Weekly, August 19, 1925, describes a new shortwave communication system proposed by Autoveyors Ltd., featuring a compound focusing apparatus and a special relay valve designed for long-distance communication using low power.
Despite claims of improved efficiency and electromagnetic control of electron emission, practical tests conducted by Radio Press Laboratories showed disappointing results, with the relay valve performing no better than ordinary valves and exhibiting negligible magnetic control of emission.

REFERENCES have appeared from time to time in the Press concerning a new shortwave system by means of which communication is possible over considerable distances on a very small amount of power. The system which is controlled by Messrs. Autoveyors, has been claimed to make communication between London and New York possible on a power of only half a kilowatt. In order to ascertain exactly what this new system was and where it differed from the existing methods, I obtained a special interview with Mr. A. E. Chapman, Technical Director to Messrs. Autoveyors, Ltd. It is understood that details of the system which it is proposed to adopt.

Short Wave Transmission
We are able to give here some indication of the method which it is proposed to adopt.  It is, by now, a well-known fact in shortwave working that the influence of the Heavyside (Ionosphere) layer upon transmission is very considerable. One effect of this layer of ionised atmosphere is that wavelengths that are suitable at certain times of the day are of no use at all at other times. Transmission between any two points, therefore, is usually accomplished by the use of several wavelengths and by appropriate changes of wavelength at different times of the day practically continuous communication can be established. Recent developments have certainly indicated that there may be bands of wavelengths which are equally effective throughout the twenty-four hours, but information on this point is not yet by any means complete.

Polarisation of Waves
Another aspect of the question. which may possibly have even more influence than the previous one, is the rotation of the plane of polarisation of the wave. That is to say, the electric field is not vertical or nearly so, as in the case of the longer wavelength radiations, but may be tilted at various angles and may even rotate in its transit from point to point. Some such action as this was indicated in the '' Inventions and Developments" column of Wireless Weekly, Aug 5, 1925, Page 571.  Certain shortwave experimenters have certainly noticed that by tilting their receiving aerials they can obtain better results.

Compound Focus Apparatus
Comparatively short wavelength radiations can be reflected by means of suitable apparatus in a similar manner to the reflection of light by a mirror. Beam systems are at present in use and in the course of erection, in which the radiations are focussed in a horizontal plane but not in a vertical plane. That is to say, although the radiations are not permitted to spread out in all directions over the earth's surface, but are limited to the confines of a certain more or less parallel beam they are enabled to spread in a vertical direction to any extent.

Restricting Beam to Solid Ray
If a second focussing arrangement could be incorporated into the apparatus by means of which the rays would be kept within the confines of a certain vertical beam as well as a horizontal beam, a more or less solid ray would be emitted from the transmitting point. This, briefly, is the outline of the system which is proposed by Autoveyors, Ltd. By the use of what is termed compound focussing apparatus the radiations are to be emitted from the transmitting point in the form of a more or less solid ray, and at the receiving point the receiver is to be in the form of a simple oscillator pivoted about its middle and capable of rotating in any direction. By this means it can be placed in the most suitable position at each time of the day to allow for the variations in the plane of polarisation of the electromagnetic wave radiating from the transmitting point.

Magnetic Fields
It is claimed that this system makes use of the magnetic field in the wave rather than the electrostatic field. We presume that what is meant is that the system does not employ any earth connection, but that the radiating and receiving systems are more of the nature of Hertzian oscillators than of the ordinary aerial and earth transmitting arrangements.
It is, of course, well known that the electric and magnetic fields of a wireless wave are inseparable, being merely different manifestations of the same phenomena, but it is sometimes more convenient to regard the effects from a magnetic point of view.

 A new Type of Valve
An important point in connection with this new system is the use of a special type of valve. One of the chief difficulties encountered in dealing with the very high frequencies necessary to produce ultra-short waves lies in the capacity effects experienced with the ordinary types of valves. In this system, therefore,  a special form of valve relay is employed in which the tuning coils are incorporated into the electrodes themselves. The device consists of a filament of wire surrounded by two spirals, which are termed the " rack " and the " helix," corresponding to the grid and the anode in an ordinary valve. The ends of these spirals are brought out to separate connections on the ends of the valve, so enabling the high-frequency oscillating current to be passed round the electrodes themselves. By this means it is claimed that an electromagnetic control is obtained on the electrons emitted from the filament, and the effect of interelectrode capacities is minimised.

The Receiving Circuit
A circuit incorporating these new valves is shown in Fig. 1. 

There are two types of valves, known as the positive and the negative types. In one of these, the spirals are wound clockwise, while in the other they are wound anticlockwise. It is claimed that the aerial currents, which flow around the " racks " of the relays, exercise a magnetic control on the emission.

" Push-pull " Arrangement
Due to the reversing of the direction of the spirals in the negative relay, it is claimed that the increase of current in the positive relay is accompanied by a decrease in the negative relay, and vice-versa, so giving a '' push-pull" arrangement. For scientific reasons, we do not agree with this explanation. We were informed that this relay is very much more sensitive than the ordinary valve, and in one form or another, it is used in all the apparatus embodied in this new system.

Practical Tests
It is understood that this type of relay will very shortly be placed on the market for the use of amateurs, and although it is designed primarily for very short waves, it is claimed that by the use of suitable loading inductances, it may be used very successfully on the ordinary broadcast band of frequencies.

In order to verify this statement and find out whether there was any appreciable improvement resulting from the use of this relay, some tests have been carried out at the Radio Press laboratories, with the following results :

• The two valves were connected up in a manner similar to that shown in Fig. 1, except that loading inductances were inserted in , the '' rack '' and " helix " circuits. The output circuit, of course, contains high-frequency currents, which will be inaudible unless rectified. Hence, the output coil was tuned and applied to the grid of a valve arranged to give the usual cumulative grid rectification. The resulting signal strength was disappointing, being little, if any, greater than that obtainable with a simple single-valve set.
• A certain reaction effect was produced by coupling the " rack " and " helix " circuits together. Oscillations could be produced, but in this case, the circuit became ''floppy," which one would rather expect, seeing that the " rack " is free. The case is identical to the building up obtained in a valve having a free grid. With the idea of dispensing with any apparatus other than that proper to the relays themselves, the circuit shown in Fig. 2 was tried and was found to give results almost as loud as the original arrangement.

Magnetic or Static Control
 At this point, in order to gauge· the effect of the " rack " on the emission, one of the " racks " was short-circuited. No difference in the signal strength could be observed, so the other '' rack '' was short-circuited. The signals remained as loud as before!

In order to investigate this effect the characteristics of the valves were taken. With a filament voltage of 1.8 and a current of 0.25 amp., the emission (with an H. T. voltage of 60) was 1.45 milliamps. The passage of current through the "rack," in either direction, had practically no effect.

A current of 0.5 amp. through the "rack " increased the emission by 0.015 milliamps, irrespective of the direction of such current. These tests appear to indicate conclusively that the magnetic control of the emission is negligible, and that any effects which are obtained are electrostatic as with an ordinary valve.

Use at High Frequency
Since these relays, however, were designed for high frequencies, experiments are in progress to ascertain whether they exhibit any superiority over ordinary valves at such frequencies. A certain benefit may accrue from the fact that the electrodes themselves can be used as part of the tuning circuits, but this will remain to be seen.

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