THE RADIO ENTHUSIAST

Radio Record, Volume IV, Issue 20, 28 November 1930, Page 7

THE RADIO ENTHUSIAST

D.X.-ing and Constructing

Outlined by

Colin W.

Smith

From 2YA

N the early days of radio there was only one type of enthusiast, and that was the man who constructed everything and had a wireless set going o: $ of the most varied assortment of odds and ‘ends imaginable. In fact, in those days the only man who listened was the enthusiast, for it required a vast technical. knowledge to operate a set. With the improvement of radio generally and more particularly with the improvement of parts, it became unGonomical to manufacture all one’s emponents, The manufacturers could, turn them out much cheaper and better than ever they could be made, and so the enthusiast confined his attention to making up and trying different circuits. jurthermore, the amateur receiving en . thusiast became different from the transmitting man. But now a third class has come into being, and very often they know nothing of the-techni-‘ealities of radio. In: fact, they do not know what is beyond the dials of their set, but they are extremely interested in radio and their chief object in their radio life is to recéive long-distance stations. These people keep most un canny hours, and sometimes receive some very weird stations. These people we ‘all the DX enthusiast, DX meaning long distance. We still find a large number of peo~ple interested in the construction of sets. Although the advent of the a.c. set has undoubtedly killed a very large proportion, still there are very large numbers who cannot afford such a set, and if they want to listen, must do so on: simple home-constructed apparatus. Undoubtedly the simplest set is the erystal,. Anyone can make a erystal set, and he can do so for a matter. of a few shillings. For about three pounds he can provide a crystal set, earphones, aerial equipment, and pay his license for a year. Compare this with the £50 that has to be paid for a really firstclass 4.c. set, and you will see why constructors will not die out for a long time. , A great deal of fun can be had from constructing different types of erystal sets, but they all boil down to the same circuit, a coil of wire, the top of which runs through a erystal, through the plrones and to earth. The bottom connects with earth. Now, if you want good results a tuning-condenser is used and connected between the top and the bottom of the coil. That is simple, isn’t it? Special care is not needed to wind the coil, and the condenser may be of the cheapest type. It is not worth while paying big sums for precision made parts, but you do need a good aerial. So many people think that because they have a little set they need a little aerial-but the reverse is true, a small set a long aerial, Now, when a crystal set is working there is no reason why it should not be _ tidily installed and wires taken from \ the phone terminals and run. right through the house, so that you may have phones in any room.. Furthermore, several pairs of phones can be used from the one erystal set. Headphones are more or less comfortable and the constructor soon wants to. use a loudspeaker and thinks about

adding an amplifier. This, too, is very simple, and can be built for little cost, but there is the upkeep of the batteries. The super enthusiast will use a primary battery such as the Daniel Cells and make his own B batteries from old torch cells, but such batteries require more attention than anyone who is not keenly interested cares to give. Do not expect too much from a one-valve amplifier, as at the best of times the signals are only weak. If you want real quality from the local station you must use two valves and at least 90 volts B battery, and do not forget the grid bias. This is a small battery about 44 volts, and its use improves the tone and saves B current. With small amplifiers such as this only a small speaker can be operated, as the bigger ones are more or less insensitive. wee

ROM the two-valve amplifier or other similar small set, the enthusiast usually branches into a "specialised" division. Quite a number of them become tired of constructing and go in for a commercial set, others build a fourvalve set, such as the Browning Drake or Hammurland Roberts, or perhaps confine their attention to shortwave’ listening. The last class search for real quality from the local station. Now to these people I want to say a few words about an excellent outfit, for it is usually contended that the local station well received is far superior to the local station ordinarily received and outside stations. . Concentrating upon this question of local station reception, our attention was attracted to the new circuit developed by .Loftin and White. When the announcement was first made in America it was said that it was an almost distortionless amplifier, and succeeding tests have shown this to be true. It does away with transformers and inter. valve condensers, for the grid of one valve feeds directly into the plate of the last. Really there is nothing new about the Loftin-White amplifier, but it has been the ingenious application of an old and well-known electrical and radio principles that has made the amplifier famous.

A great deal has been written about the resistance of the Loftin-White, for it has been said that these are extremely critical, and I have seen specifications which have given resistances running into four figures right down to the last figure. This has frightened away very many who would otherwise have built it, but I ean assure them that such is not the case. The main chain of resistance is not at all critical. They merely take the place of the voltage divider in the ordinary eliminator, and constructors know how this can be altered without any material effect.

What are critical, however, are-the bias resistances, and, unfortunately, some of the gridleaks are not at all accurate, and may be 500,000 ohms at fault. But their replacement is a matter only of 2 shilling or two. The original amplifier used the 224 screen grid and the 250 and later the 245 power-valves. It was soon shown by experimenters, mainly in Australia, that the power pentodes could be used in the last stage with advantage. There are, however, certain objections to the use of the pentode in the Loftin-White and, I think, a better valve for the last stage can be found than either the 245 or the pentode. At the present time we are working on a new combination which I believe will give unparalleled quality and greater punch than the ordinary circuit. , So much for the Loftin-White. 1f have dwelt upon if mainly because there are hundreds of constructors in New Zealand who are now concentrating upon it, and also because I am very interested in it. We have just shown how radio frequency amplification can be added to make a powerful set which,

Boxing Relay The interprovincial amateur boxing tournament between Otago and Canterbury for the Waironga Shield, which takes place in the Civic Theatre, Christchurch, on Tuesday, December 2, will be broadcast by 3YA.

while no dearer than a home-made A.C. set with two more valves, can not be equalled for quality and punch. (THE country listener, who is confined to batteries, must use other circuits and, as I mentioned before, the four-valve Browning Drake or Hammurland Roberts will be his best bargain. These sets are quite simple to make and give astonishingly good results. Some, of course, do not want to go to the extent of four valves and prefer to make one or two-valve sets. These, however, can cause a considerable amount of trouble, and most of the howling valves result from users of these small sets endeavouring to reach out and get stations too far distant. The thing that is difficult to understand is that these people know that they are howling and yet still continue to do so. In some measure, to combat this trouble the New Zealand Radio Press has withheld from bringing out one and two-valve circuits, though it appears that a large number of congtructors are obtaining their information from magazines the circuits of which contravene New Zealand regulations. In order to meet this situation a new series of receivers on improved lines are soon to appear. Now I think I have said as much as time. ‘ill allow to the home constructor. We must now pass on to the other radio enthusiast, the DX man. Any set will do for DX-ing, providing it has sufficient amplification to bring in outside stations without annoying one’s neighbour. Recently I saw a curious definition of the ideal DX man’s set-a power detector, with a high gain amplifier, preceded by two stages of imag ination. Now, I don’t think that is quite fair, as although many of these fantastic stations exist more in the imagination than in reality, still I am of the firm belief that easily the largest number of real DX-ers are honest. There is no doubt that there is a considerable amount of fun to be had for searching for these unusual stations. Here are some of the times in which to search for the DX "plums," as they are called. Australian main stations during New Zealand daylight-and no imagination, please. Also, some of the small New Zealand B class stations are very difficult to receive in daylight. Most sets of four valves or more can receive the Japanese stations, which can usually be heard after 10 pm. The music is very weird, and listening to them for the first time provides a real thrill. There is one just close to 4QG, which, in the Wellington district at least, comes in splendidly. The American stations have been coming in very well this season, and Chicago is not'infrequently reported. They can usually be heard late in the afternoon and up till 8 or 9 o’clock at night, Sunday night being the best time, because they are then on later, it being their Saturday night, If you want to hear Chinese stations, it will be necessary to keep very late hours, for they do not begin to come in until the Australian stations have closed down, The Indian stations are still later, and they can usually be heard at about 2 a.m. The most prized DX scalps are the South African and Buropean stations, and surprising though it be, these have been definitely received before sunrise. At the present time there are a number unidentified stations which can be heard about 4 o’clock in the morning. Z firmly believe they are Huropean sta-

tions because very many of these operate on tremendous power, and there is no reason why they should not be heard. So far I have heard of no one who has received a verification card from any one of these, but I know a few who have written away and are anxiously awaiting a reply. It will. be very interested to know who will be the first New Zealander to receive verified reception of a Duropean broadcast’ station. ‘They were heard in the old days on the crudest of apparatus. I spoke a few moments ago about a verification card, and I know some of you will be wondering what that is. It is the only tangible proof that anyone can offer for receiving a station. The station is heard, the call-sign dis-

tinguished and some of the items and their times noted down. This, together with as many details of the reception as possible, is sent away to the station in question, and they reply by stating definitely whether it was their transmission that was heard. It is surprising just how many cards one can collect, and, I think I am not exaggerating to say that some listeners favourably situated have over 100 cards to _adorn their walls. At the present time "a competition is being held to see who can produce the largest number of these cards. One thing is necessary for good DX work-and that is a good aerial. Even then some people cannot get good results, and this is due to their situation. So many have written to me quite disappointed at not being able to receive the American stations, although

they have a good set, but ‘all the consolation that I can offer, is that I have , a splendid aerial and have tried on almost qgll the first-grade sets there are; \ and am unsuccessful, yet I know an enthusiast who lives less than two miles away who received them regularly.