Long and Short Aerials

Radio Record, Volume II, Issue 26, 11 January 1929, Page 29

Long and Short Aerials

Comprehensive Research by Correspondent

A BE. ELLESTON, writing from * Reefton, states his conclusions on the use of long and short aerials for broadeast work. Many valuable conclusions have been arrived at, and listeners who desire the best results can do no better than to consider the’ results obtained by Mr. Elleston. IN looking through the pages of the "Radio Record,’ I have noticed writers wishing to know of practical results achieved with equipment not used in the ordinary way for wireless reception. I am therefore writing you of results which I have obtained with long aerials. I do not pose aS an authority on aerial systems, the results of my experiments are given for what they are worth, and in the spirit that we learn from one another, either verbally or recorded. The Long and Short Aerials. ror nearly four years now I have hag two aerials, one 512ft. long and the other 125ft., the former is 7/22 copper and the latter No. 16: The aerials are at right-angles to one another, and are directional, the long one to Sydney, the other to the New Zealand stations. The set used in the experiments is a three-valve reflex, aerial coming direct to the grid, and is tuned by a .00035 variable condenser. In addition,- there is a variable neutralising condenser of two plates, the plates are very close together, and for safety sake are painted with an insulating substance. The aerial on which the experiments were made is, as stated, above 512ft. long, it is supported by an iron pipe mast 50ft. high at the receiver end. The other mast, 36ft. high, is on an abrupt hillside, the top of this mast is 116ft. higher than the other. The first thing was to note the difference in condenser readings between the long and short aerials, using one ground, and that having a fixed condenser in it. Readings were three degress less on 1, 2, and 8YA. Signals as a genera] rule are a great deal louder

than on the short aerial, it being more marked on days when signals are weak and in daylight reception. More noise is picked up. On the day of the Heeney-Tunney fight, the short aerial provided better reception than did the long one, though in many cases it has been vice versa, At times, the long aerial provided entertainment when nothing could be heard on the other. There is a certain amount of broad tuning, in my casé it does not intrude very much. When noises are absent, the long aerial is an advantage. The long aerial is a great advantage to a set using a crystal detector.

My set is designed for.selectivity and volume, so far I have not required a wave-trap. Effect of a Ground. THEN tried the effect of a full ground on each end of the long aerial, making the length 550 feet, and direct to grid. The effect was that of a gigantic loop. As I have an eliminator with a condenser in the ground lead, I tried that way for a start; the set refused to function. I then replaced the eliminator with dry batteries, there was then no difficulty in getting it to function, that is with two complete ground wires. The set became more difficult to work, with a wider swing for the neutralising condenser; it did not respond to this condenser so well in the lower as in the higher wavelengths. Clarity was much better with two grounds than when the aerials were worked under ordinary conditions, Tuning was broad, volume was much EE eT

the same as under ordinary conditions, but greater volume could be had before distortion was reached, than under ordinary conditions. Dial readings on aerial condenser were the same on high wavelengths. and three degrees less on low wayelengths. The secondary condenser was not affected. Daylight reception at noon of 2YA was at loudspeaker strength, but the noise was also loud. The absence of noise was an advantage of the short aerial; dial readings were three degrees less in daylight. I have tried the Beveridge plan with high resistances from 2 megohms down, but find full grounds results best. My observations in the constant use of iong and short aerial with one ground, over a number of years, has shown me that it is an advantage to have. two aerials, short and long. They can be used in the country where there is room, and freedom from interference, and power line noises. An: other thing is that country people retire early, and at this time of the year the long aerial will, in most cases, give the mecessary loudspeaker volume. Concerning Long Aerials. TH following excerpt is from a well-known authority in a letter to me concerning long aerials. "The pick-up value of an aerial depends partly on the fact that it is an open condenser, -with associated inductance. Maximum effect is produced by tuning ‘to resonance. Losses are avoided by keeping the capacity as open as possible (height). insulation, low R.F. resistance, and keeping couductors out of the field. But there is another consideration generally ‘overlooked. ; "The mere length of an aerial may have an appreciable effect owing to increased collecting surface, and a more important effect owing to the occurrence of stationary waves with nodes and anti-nodes on the aerial itself. This will be a maximum when the length

is such that a-voltage node occurs at the ground, and a current node at the open end of the aerial. Obviously this effect will be most pronounced when the aerial, measured simply as a long conductor, is approximately quarter wave-length, three-quarter wavelength, one and a-quarter wave-length, ete. "Other things being equal, then, we should get an improvement up to quarter wave-length, a falling off up to half wave-length, further improvemeut up to three-quarter wave-length, and so on. Owing to the double tuning effect, however, the resonant peaks wil] probably’ be flatter. "I certainly do not condemn long aerials, except on the ground of expense and difficulties in the way of muintaiaing efficiency." -( "Proton," "Lyttelton ‘Times.’ ) With the Browning Drake. JT have used the long aerial with one ground on yarious sets. A _ portable B.D. used by an agent of a wellknown firm, was tried on 2BL. It was not strong on ’phones with the short aerial, buc gave good loudspeaker strength with long aerial, as well as timing sharply. I have not experimented with long aerials on short-waves, but have been given to understand that they are used in commercial stations. In the near future the writer will replace his first valve with a screened grid, and the third valve with a 5 electrode in his reflex circuit, and will carry out further experiments with long aerials. I consider the "Radio Record" 4 very fine little paper, with much of interest in it.