This is based on something I learned to do when I was 13 and fooling around in the back of an old radio. Because the radio was poorly grounded and I did not unplug it, I was mildly shocked, in the same way a cow up against an electric cattle fence is shocked (no permanent damage, I think, or maybe so much that I don’t know the difference). I stress that you take every precaution against electricity. Your best bet is to use a hand-held radio. It’s easier, not dangerous and it’s just as good. BE CAREFUL.
What you need:
A small, easy-to-open AM (same as mediumwave) radio. When choosing a radio to convert, consider the perfection of a hand-held transistor radio. You can theoretically do this with any radio, but desktop or home stereo models are usually more difficult to get into, involve higher voltages and more sensitive parts. I’ve converted more than 20 radios in this way, and have found that US$10 children’s radios with no FM band and a large, friendly thumb wheel for tuning work perfectly. You should avoid Walkmans and anything with a combo cassette player; they usually have inferior AM radios, small tuning wheels and a ridiculous number of screws to loosen to get at parts. Don’t use anything with digital tuning.
Two pieces of 12 gauge or smaller insulated (or shellacked) wire, one about 24 inches (60 cm) and one about 48 inches (121 cm) or greater. Wire typically used in telephone switching boxes works great, but you can also use magnetic wire spooled off of an old motor. For the short wire, the smaller the gauge of the wire, the longer the piece should be. Remember that your wire’s insulation should be good with no breaks or bare places, except for about an inch at each end
Tools. Usually a screwdriver at most. Will vary according to radio.
You may need a good braunschweiger sandwich with mustard and cheddar as reinforcement. Kaiser rolls are best, but a powdery Portuguese roll will work.
1. Disconnect the battery or power source. REMEMBER, if you are using a model that plugs into the wall, you must unplug the radio at least ten minutes before you start to let any charge dissipate. You could get shocked or damage parts (yours and the radio’s) if there is a charge left in a capacitor or transformer. You may want to ground yourself electrically. I recommend doing this while sitting on top of a metal radiator or you might consider wrapping yourself in heavy duty aluminum foil. Just kidding. Be careful.
2. Open the case and look for the tuning coil. It could be on either side of the green circuit board. The tuning coil is on an iron (ferrite) rod, dark in color with a matte exterior, usually cylindrical with flat ends, often with beveled sides. The rod varies in length (usually two to four inches, or 5 to 10 cm), but is easily recognized by the fine orange/copper wire that is wrapped around it, usually on top of waxed paper. There is nothing else like it in the radio. Usually, the bigger the radio, the bigger the ferrite rod.
3. Loosen the rod in such a way as to remove it from the chassis but not disconnect the wires attached to it. Be careful, because these wires are difficult to reconnect. There is usually not a lot of slack in them. Sometimes the rod is held in place by wax; other times it is held in place by a plastic fastener screwed to the circuit board.
4. Starting at one end, wrap your short wire around the coil that is already on the iron rod. For now, leave about four inches of wire free to dangle at each end of your new coil. The coil already there should be completely underneath your new coil. [On some radios, the existing coil is separated into two parts. Wrap your coil around both parts. Later you can test for effects to see what happens if you wrap it around only one part]. Each turn of your new coil should touch the last turn, until you reach the end of the coil already on the rod. Don’t overlap your own wire as you wrap it. If you find that you cannot create a new coil around the old without covering some of the wires leading from the old coil to the circuit board, do so, but be careful not to damage them or short them. Make sure you still have plenty of slack at both ends of the coil you are creating.
5. Replace the iron rod (now containing the overlapping coils), and refasten it.
6. Run the two free ends of your coil from the case. You can run them out holes in the speaker grill, apertures you’ve carved in the back or side, or slip them through the battery compartment.
7. Close the case. Reconnect the battery or power. 8. Connect the two free (and bare) ends of your coil and a bare end of the long wire in a simple twist. The long wire is your antenna. You now have a shortwave radio.
Things to Remember: If you are unfamiliar with shortwave, know that it works best at night in the range typically covered by this conversion. In the evening your dial will be so filled with stations, you will have to tune s-l-o-w-l-y in order not to skip past stations. If there are strong or very close AM (medium wave) transmitters nearby, they may bleed through. There will be repetition when you tune down the band. That is, strong shortwave stations will image themselves in more than one place on your tuning dial. So if you have interference, keep tuning down the band to find a clearer image. The AM stations that bleed through will not show up as multiple images. Also, even though there is repetition, keep tuning to find other stations beyond the range of repetition. The same images will not repeat for the entire the length of the dial. Depending on how many turns you made, your tuning range will vary, but I estimate that it covers from about 5 MHz to 15 MHz, more than enough for decent listening. Your tuning coil will no longer act as a directional antenna for medium wave.
Variations: Try untwisting the two ends of your coil and connecting the antenna to each end in turn. You should notice that during the day one of these connections will boost your AM reception substantially (but may also overload the radio or allow strong stations to bleed excessively). The other connection will provide shortwave reception, but will shift the tuning range of the radio (compared to when both ends of the coil are attached to the antenna) and will allow AM stations to bleed through more than if the two ends of the turn and the antenna are twisted together.
Try just wrapping part of the coil. May change the tuning range.
Try fewer wire turns spread across the length of the old coil. May also change the tuning range.
Try a longer antenna. Be careful not to overload your radio. If you use a really long wire, ground it to reduce static and interference.
Try grounding one of the ends of your coil to a fire escape, steam pipe or other huge metal object and attaching the other to your antenna.
Try a different gauge of wire for your coil.
Try connecting one end of your antenna to one end of your coil and the other end of your antenna to the other end of your coil.
Try replacing the tuning dial with a much bigger wheel (they are usually held on by a single screw). You can make them out of stiff cardboard, or, if your radio case will allow, even a large lever that will give you Super Torque Tuning. Any of these will create more precision when tuning down the dial.
The variations are endless.