An Interesting Phenomenon

Radio Record, Volume IV, Issue 39, 10 April 1931, Page 17

An Interesting Phenomenon

Correspondent’s Experience I WOULD like with your permission to give readers, more particularly those interested in construction, a very interesting result of one of my experiments, and as I frankly admit that it has me puzzled, I have no doubt some of your more experienced readers will try the thing out and give an explanation thereof. My set is a battery model six-valve factory-made job, and is recognised. as a very efficient set. However, since purchasing this set, the screen" grid valve made its appearance, asd in order to get the benefit of 8.G. amplification without interfering with the set, I constructed a §8.G. Booster. This gave the set an extra kick, and satisfied me that the screen grid valve was a decided improvement. I then constructed the crystal set and wave trap described in the 1929 "Radio Guide." This gave me wonderful reception on the local. station on two valves. by plugging into the detector socket of the big set. One evening while "listening-in" .to 2HC with the booster attached, the local 2YA was heard in the background with too much volume, so I decided to try hooking up the wave trap as well, with the result that 2YA disappeared. So far so good. The following evening our old friend static was on the warpath; and in disgust I decided to give it the full possession of the ether. and go to bed. At this time the apparatus on the table was connected up as follows :- Static can be accentuated by the action of the crystal in this circuit, where it is acting as absorption tuned circuit in series with the aerial there by sharply tuning the aerial circuit. By disconnecting the earth selectivity is increased. As the mains were acting as an aerial, and the unwanted signal was absorbed by the previously tuned circuit the crystal, you were able to add to your signal strength. This may seem a fearsome hook-up t» tune in a station on, but I was getting some fun out of it, so why worry? I disconnected the aerial from the crystal set in preparation of closing ‘up for the evening, but instead of the musie ceasing as I expected, it came in louder, and what was more, old man static must also have been surprised, as he was decidedly less noisy. I then disconnected the earth from the main set, and the result was that 2FC, Sydney, came in as loudly as 2YA, and static was not heard-2YA was also cut right out. Now, according to all the text books on radio, a good earth and aerial are the first essentials to good reception, and here was I getting a Sydney station without aerial or earth. Needless to say, I did not go to bed as I intended, but sat up till the early hours. I was able to tune-in all the A class Australians and quite a . number of "Japs," and also about 15 B class stations in New Zealand and Australia. But what impressed me more than anything was the absence of static and background noises that were apparent with the aerial and earth connected up. I should have explained earlier that I use a "B" eliminator. The only as-

sumption I can arrive at is that the eoil of the erystal set was acting as an aerial, and that the mains were earthing the whole hook-up. Incidentally the tuning is extremely selective, about two degrees of the-booster dial being sufficiemm to cut cut any sbation-A Comfort (Wellington), We Suggest. OUR experience is quite a common one, except that the crystal set acted in.a different manner from what it was constructed for, and by way of a change became an absorption wave trap. The mains acted as aerial and ground. This is a feature in some localities that is quite objectionable, resulting in unwanted signals impinging on those that the set is tuned to, with the result that special circuits have to be divised in the main heads to reject them. Otherwise the set would be blamed for being unselective, Here is another peculiar and inter esting method: Connect aerial and earth to erystal set. Place the other set in a slightly oscillating condition. Now carefully tune crystal set a little distance away from the other set (but do not place phones in crystal set). and note effects. In some cases: signals tuned in on the erystal set will be reproduced in the other set, although.

not audible on the crystal set. Remember, that in playing with sets great discoveries may be made accidentally, so pass them along for the benefit of others. Armstrong discovered reaction by playing with a coil of wire while receiving signals.-Tee. Hd.