QST, №3, Fabruary, 1916, p. 22-23


By a League Member

A friend, thirty miles from my radio station, had installed a half kilowatt transmitting set, but was unable to communicate with me. He had been asking me to come out and look his station over; he felt quite sure that everything was O. K., but wanted me to suggest improvements. One snowy afternoon in December I took the — Railroad to his town which was located in the southern part of New York State. It was a onehorse town which boasted of a wireless station but no trolley cars. As my friend had no car, I was compelled to plow my way through no less than six inches of snow, but I finally reached his home and was no sooner inside the door than he unceremoniously dragged me off to see his set.

"Well, Brother, what do you think of this? I've got it arranged pretty nicely; haven't I?"

I gazed around and the first thing that attracted my attention was an oscillation transformer fastened on the ceiling. Two long, straggly wires came down from this to a condenser on the operating table. Six more straggly wires drew my attention to a porcelain tube in the floor.

"Where do those go?" I inquired, pointing at the wires.

"Oh yes, that is a clever little idea of my own. You see, this plaguey rotary is such a confoundedly noisy affair that I put it down cellar with the transformer," explained the genius.

"Yes! I suppose your aerial switch is on the roof so you can have it near the aerial," I snorted in disgust.

"Well, what's the matter, you old Grouch? Anyway, the receiving set is all right; isn't it?"

"Yes, because fortunately it's all in one unit and you didn't have a chance to scatter the instruments around as your fancy dictated. Of course, I suppose, if you had had the opportunity, you would have put the audion bulb out on the front door so that people might know you have a wireless station. But, all joking aside, I really believe I shall have to give you a short talk on the fundamental principles of wireless," I said, as I thought out my lecture.

"Ga, Ga, —.—," he signed.

"Well, in the first place, you have a condenser which is charged from your high voltage transformer. This condenser discharges through your rotary gap and primary inductance of your oscillation transformer. By adjusting the condenser and primary inductance, you can obtain your two hundred meter wave length." (Fig. 1)

"Just how much condenser and inductance must I have," broke in my listener.

Cautioning him about the QRM I remarked, "If you have twelve glass photograph plates, eight inches by ten inches, coated with six by eight inch tinfoil, and a loop of inductance about eight and one-half inches in diameter, you will get a two hundred meter wave. Now the object of this primary circuit is to stow up energy in the condenser and then make it flow through the inductance. The longer you make your inductance, the greater will be your wave. This means, if you have a great many long leads connecting the condenser, spark gap, and oscillation transformer, you will build up the wave and will lose energy in the long conductors instead of centering it in the primary of your oscillation transformer.

"Next, the primary inductance must readily give up its energy, to the secondary, but the secondary must not re-act back on the primary. This means a fairly large degree of coupling between the primary and secondary of the oscillation transformer. Too close coupling will make your decrement high and this is hardly desirable. To make the secondary circuit absorb the greatest amount of energy, you must make its wave length equal to the wave length of the primary circuit. You see, it's a very neat little arrangement. The primary circuit is nothing but a condenser, gap, and inductance. The secondary circuit is very similar to the primary; you have the secondary inductance and the condenser effect is obtained between the aerial and ground as shown by the dotted line in Fig. 2.

"Now I can probably begin to argue about the arrangement of your apparatus. You can see how important it is to have the leads short that you may not lose energy. By short, I mean about a foot for each connector. In your case, the leads are probably five feet long on an average. If you had placed your oscillation transformer, gap, and condenser close together, it would have been possible to cut the length of the connections down to two feet. Suppose you had placed the oscillation transformer directly above the condenser and near the side of the condenser there would be room for the rotary."

"Well if I do that, I'll have that noisy thing up in my room. Besides, it will litter up my table," objected the listener.

"Well, of course, if you are fixing up your set to look at, have your own way, but if you want to talk with somebody, take my advice and arrange your apparatus not for looks but for short leads. Try it in several positions and find out which works best. Then you should connect it with wire of respectable size; perhaps, No. 8 instead of 18. Copper ribbon is very good, but stranded wire is better. As to the noise, why don't you put your rotary in a box, or buy some kind of a quenched gap?

All these things which I have suggested in regard to your sending apparatus apply to the receiver. In your case, the receiving set seems fairly efficient as you have purchased it in a complete unit. Just let me give you a bit of general advice concerning your operating table. You work your station right-handed. I am also right-handed and I have always found it a good plan to have the receiving apparatus on the left with the aerial switch, then the key and finally the sending. That gives you a chance to change quickly from sending to receiving. You will find it very convenient.

"I suppose we might even improve your aerial," I suggested. "You might raise it a few feet to clear some general obstruction, and again you might help things a great deal by straightening your lead-in and using a large wire or a better ground. I'm sorry that it's so dark tonight, but some time I'll come out earlier and we can look over your aerial. For the time being, I guess you will be busy enough looking over your set and trying to get the right arrangement. As it is now, I don't suppose you are sending ten miles, but fix it up and you will be able to talk with me."

Then, we had dinner and after receiving his many thanks and numerous blessings, I started out on my mile walk through the one horse town and seven inches of snow. I was convinced that this visit had been a help to my friend. If I only had the time, I should like to visit several hundred other amateur stations which need improvement.

MORAL: Arrange your apparatus in an efficient way; make the leads short; use copper ribbon or stranded wire; work for the best combination.