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This antenna has been around for decades and the design is as basic as can be.
Somehow the antenna I'd been using, became unwound. The total length of the wire is 4.9ft.
I need to know the proper technique, if any, to simply rewind the wire. I rewound the wire but the result was only static. So, I don't think I did it right.
The loop antenna is pictured.
There is no special precise construction to these antennas — they are just wire wrapped around an inert plastic frame. It does not matter (significantly) how the turns (wraps) lay next to each other. You should make sure that the number of turns is the same as it was originally, but that should be fairly obvious based on using all of the wire that came off it.
If the antenna no longer works at all, it is likely that the wire is broken somewhere. You can check this with a multimeter — set it to continuity or resistance mode and probe the two wire ends on the cable, and you should see a very low resistance.
If the wire is broken, you can replace it with fresh wire.
You do not need any special wire to do this — just insulated stranded wire that is not so thick that it doesn't all fit, nor so thin that it breaks with normal use.
Measure and cut the same length as it used to be (as measured by number of turns around the frame), plus extra to be the “feed line” running to the receiver (that can be any length).
Wrap the wire around the frame, making sure you have enough free length on both ends. (Starting from the middle of the piece of wire might be a good idea.)
Once you've wrapped the right number of turns, make sure the wire is snugly settled down; there is probably a notch in the plastic which you can use to help hold the wire in place. A little hot-glue might not be a bad idea.
Take the two wires coming away from the antenna and twist them together along their length, similar to how the little length of paired wires visible in the bottom left corner of your picture is, but all the way to the ends.
Connect the ends to the two antenna terminals on your receiver.
You should also feel free to experiment with constructing a new antenna with a different frame, if you like. The plastic doesn't matter; you can use any material that is not conductive (wood, cardboard, PVC pipe, etc.) to physically support an antenna. A larger antenna (bigger area enclosed by the loop) will receive signals better (up to a point); more or fewer turns (different impedance) might also make a difference but a less certain one.
A similar-looking (Sony) antenna (12.5cm x 10.5cm) was measured on a 1kHz bridge as 24 microhenry.
The bridge "Q" was very low as expected at 1kHz (well below 1), but gave a good null for its inductance value.
A second test added a parallel capacitor of 560 pf. and measured with an oscilloscope's 10X attenuator probe. A sharp resonance at 1400 kHz resulted...that jives with a 24 uH inductance. Self-resonant frequency was above 5 MHz.
It seems to be a simple coil of wire, with electrical inductance of 24uH. Seems to be made up of PVC-insulated wire in a single-layer winding of 8 turns, close-wound spanning nearly 1cm.
It is possible that the antenna inductance of 24uH is used with a resonating parallel capacitor inside the radio to tune the AM broadcast band.
Most coil calculators assume a round coil form rather than this "square-ish" form. I had formerly included results from Bob Lombardi's AIRWNDL.EXE coil calculator program. Bob didn't describe his equation - it assumed a round coil form.
A rectangular-loop coil calculator yielded an inductance of about 28uH given the following parameters:
Be aware that the actual coil form is less than a strict rectangle, so measured inductance of 24 uH is still reasonable.
