The Radio Amateur's Hand Book, by A. Frederick Collins is part of HackerNoon’s Book Blog Post series. You can jump to any chapter in this book here: [LINK TO TABLE OF LINK]. Chapter XI: Short wave Regenerative Receiving Sets
XI. SHORT WAVE REGENERATIVE RECEIVING SETS
A short wave receiving set is one that will receive a range of wave lengths of from 150 to 600 meters while the distance over which the waves can be received as well as the intensity of the sounds reproduced by the headphones depends on: (1) whether it is a regenerative set and (2) whether it is provided with amplifying tubes.
High-grade regenerative sets designed especially for receiving amateur sending stations that must use a short wave length are built on the regenerative principle just like those described in the last chapter and further amplification can be had by the use of amplifier tubes as explained in Chapter IX, but the new feature of these sets is the use of the variocoupler and one or more variometers. These tuning devices can be connected up in different ways and are very popular with amateurs at the present time.
Differing from the ordinary loose coupler the variometer has no movable contacts while the variometer is provided with taps so that you can connect it up for the wave length you want to receive. All you have to do is to tune the oscillation circuits to each other is to turn the rotor, which is the secondary coil, around in the stator, as the primary coil is called in order to get a very fine variation of the wave length. It is this construction that makes sharp tuning with these sets possible, by which is meant that all wave lengths are tuned out except the one which the receiving set is tuned for.
A Short Wave Regenerative Receiver--With One Variometer and Three Variable Condensers.--This set also includes a variocoupler and a grid coil. The way that the parts are connected together makes it a simple and at the same time a very efficient regenerative receiver for short waves. While this set can be used without shielding the parts from each other the best results are had when shields are used.
The parts you need for this set include: (1) one variocoupler; (2) one .001 microfarad variable condenser; (3) one .0005 microfarad variable condenser; (4) one .0007 microfarad variable condenser; (5) one 2 megohm grid leak; (6) one vacuum tube detector; (7) one 6 volt A battery; (8) one 6 ohm, 1-1/2 ampere rheostat; (9) one 200 ohm potentiometer; (10) one 22-1/2 volt B battery; (11) one .001 microfarad fixed condenser, (12) one pair of 2,000 ohm headphones, and (13) a variometer.
The Variocoupler.--A variocoupler consists of a primary coil wound on the outside of a tube of insulating material and to certain turns of this taps are connected so that you can fix the wave length which your aerial system is to receive from the shortest wave; i.e., 150 meters on up by steps to the longest wave, i.e., 600 meters, which is the range of most amateur variocouplers that are sold in the open market. This is the part of the variocoupler that is called the stator.
The secondary coil is wound on the section of a ball mounted on a shaft and this is swung in bearings on the stator so that it can turn in it. This part of the variocoupler is called the rotor and is arranged so that it can be mounted on a panel and adjusted by means of a knob or a dial. A diagram of a variocoupler is shown at A in Fig. 53, and the coupler itself at B. There are various makes and modifications of variocouplers on the market but all of them are about the same price which is $6.00 or $8.00.
The Variometer.--This device is quite like the variocoupler, but with these differences: (1) the rotor turns in the stator, which is also the section of a ball, and (2) one end of the primary is connected with one end of the secondary coil. To be really efficient a variometer must have a small resistance and a large inductance as well as a small dielectric loss. To secure the first two of these factors the wire should be formed of a number of fine, pure copper wires each of which is insulated and the whole strand then covered with silk. This kind of wire is the best that has yet been devised for the purpose and is sold under the trade name of litzendraht.
A new type of variometer has what is known as a basket weave, or wavy wound stator and rotor. There is no wood, insulating compound or other dielectric materials in large enough quantities to absorb the weak currents that flow between them, hence weaker sounds can be heard when this kind of a variometer is used. With it you can tune sharply to waves under 200 meters in length and up to and including wave lengths of 360 meters. When amateur stations of small power are sending on these short waves this style of variometer keeps the electric oscillations at their greatest strength and, hence, the reproduced sounds will be of maximum intensity. A wiring diagram of a variometer is shown at A in Fig. 54 and a basketball variometer is shown complete at B.
Connecting Up the Parts.--To hook-up the set connect the leading-in wire to one end of the primary coil, or stator, of the variocoupler and solder a wire to one of the taps that gives the longest wave length you want to receive. Connect the other end of this wire with one post of a .001 microfarad variable condenser and connect the other post with the ground as shown in Fig. 55. Now connect one end of the secondary coil, or rotor, to one post of a .0007 mfd. variable condenser, the other post of this to one end of the grid coil and the other end of this with the remaining end of the rotor of the variocoupler.
Next connect one post of the .0007 mfd. condenser with one of the terminals of the detector filament; then connect the other post of this condenser with one post of the .0005 mfd. variable condenser and the other post of this with the grid of the detector, then shunt the megohm grid leak around the latter condenser. This done connect the other terminal of the filament to one post of the rheostat, the other post of this to the - or negative electrode of the 6 volt A battery and the + or positive electrode of the latter to the other terminal of the filament.
Shunt the potentiometer around the A battery and connect the sliding contact with the - or zinc pole of the B battery and the + or carbon pole with one terminal of the headphone; connect the other terminal to one of the posts of the variometer and the other post of the variometer to the plate of the detector. Finally shunt a .001 mfd. fixed condenser around the headphones. If you want to amplify the current with a vacuum tube amplifier connect in the terminals of the amplifier circuit shown at A in Figs. 44 or 45 at the point where they are connected with the secondary coil of the loose coupled tuning coil, in those diagrams with the binding posts of Fig. 55 where the phones are usually connected in.
Short Wave Regenerative Receiver. With Two Variometers and Two Variable Condensers.--This type of regenerative receptor is very popular with amateurs who are using high-grade short-wave sets. When you connect up this receptor you must keep the various parts well separated. Screw the variocoupler to the middle of the base board or panel, and secure the variometers on either side of it so that the distance between them will be 9 or 10 inches. By so placing them the coupling will be the same on both sides and besides you can shield them from each other easier.
For the shield use a sheet of copper on the back of the panel and place a sheet of copper between the parts, or better, enclose the variometers and detector and amplifying tubes if you use the latter in sheet copper boxes. When you set up the variometers place them so that their stators are at right angles to each other for otherwise the magnetic lines of force set up by the coils of each one will be mutually inductive and this will make the headphones or loud speaker howl. Whatever tendency the receptor has to howl with this arrangement can be overcome by putting in a grid leak of the right resistance and adjusting the condenser.
The Parts and How to Connect Them Up.--For this set you require: (1) one variocoupler; (2) two variometers; (3) one .001 microfarad variable condenser; (4) one .0005 microfarad variable condenser; (5) one 2 megohm grid leak resistance; (6) one vacuum tube detector; (7) one 6 volt A battery; (8) one 200 ohm potentiometer; (9) one 22-1/2 volt B battery; (10) one .001 microfarad fixed condenser, and (11) one pair of 2,000 ohm headphones.
To wire up the set begin by connecting the leading-in wire to the fixed end of the primary coil, or stator, of the variocoupler, as shown in Fig. 56, and connect one post of the .001 mfd. variable condenser to the stator by soldering a short length of wire to the tap of the latter that gives the longest wave you want to receive. Now connect one end of the secondary coil, or rotor, of the variocoupler with one post of the .0005 mfd. variable condenser and the other part to the grid of the detector tube. Connect the other end of the rotor of the variocoupler to one of the posts of the first variometer and the other post of this to one of the terminals of the detector filament.
Connect this filament terminal with the - or negative electrode of the A battery and the + or positive electrode of this with one post of the rheostat and lead a wire from the other post to the free terminal of the filament. This done shunt the potential around the A battery and connect the sliding contact to the - or zinc pole of the B battery and the + or carbon pole of this to one terminal of the headphones, while the other terminal of this leads to one of the posts of the second variometer, the other post of which is connected to the plate of the detector tube. If you want to add an amplifier tube then connect it to the posts instead of the headphones as described in the foregoing set.
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Collins, A. Frederick. 2002. The Radio Amateur's Hand Book. Urbana, Illinois: Project Gutenberg. Retrieved April 2022, from https://www.gutenberg.org/files/6934/6934-h/6934-h.htm#chap11
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