Rap 'n Tap
[ Home | Contents | Post | Reply | Next | Previous | Up ]
From: Mike h
Date: 8/26/00
Time: 8:53:15 PM
Remote Name: 12.82.140.253
Harvey, some time back either here on Rap n' Tap or on the Yahoo club site someone told how to make such an antenna enhancer. I made one, and it works great. Not, however, for any of my xtal sets. I believe these loop antennas are used for amplified AM radios which can respond to small increases in signal strength with dramatic results at the speaker. Even a long-wire xtal antenna doesn't provide enough current, as far as I can tell, to enable these small loop antennas to add any appreciable volume to xtal reception. I will, briefly, try to explain how I made mine and under what conditions it worked.
The article I mentioned gave both the formula for maiking the antenna and a quick description of the one I copied. I will just describe the one I built by those instructions:
Hash together a wooden or plastic frame about 12" square and an inch or so wide. An old picture frame about that size will work, or a cardboard box bottom with an inch or so of the sides left attached. That's a workable frame for the coil you will wind on it. Don't sweat the details at this point concerning materials, loss, precise length of windings and such. In time someone might offer good advice about such things, but I'll garantee you some noticeable results with these rough-n'-ready instructions.
Now Poke or drill a small hole through one corner of the frame, run a foot or so of wire through that hole and tape or hank it off so it won't pull out then wrap onto the outside of the frame 20 wraps of some small wire wire, either insulated or enameled magnet wire. Don't sweat the size and feel free to join junk together with solder joints if you want. Just see that the wraps are spaced apart. You don't want to short between any of the wraps, right? You can glue them down with anything you want to hold the spacing, or maybe use some sticky tape or such. If you do this you can even use uninsulated wire, whatever you got. The wire can be solid or braided. If you use insulated wire like automotive stuff you don't even have to sweat the spacing, just wrap the sucker.
When you've got 20 turns on the frame, backtrack or continue on to the next corner of the frame which is directly opposite the one you put a hole in first. Run yr wire through this hole and cut it off a foot or so long like the other one.
Now you have a frame with a loop antenna on it with 2 loose ends. Make those loose ends emerge on the inside of the loop. That is, on the inside of your shallow box, right?
What you need now is a cheap variable capacitor, like one of those $2 models sold by lots of suppliers or one salvaged from an old transistor radio. Hook up one of your loop ends to one of the terminals on this cap. and the other one to the other one. Stick that little capacitor to the center of the frame with glue or wads of tape or anything.
Prop the whole thing up on a table or the ground if you're camping, turn on an AM radio, tune it to a weak station, move it up close to the frame, right in front where the capacitor is (with its knob handy). Now the trick is to orient the (directional) ferrite rod antenna that most all AM radios have in them 90 degrees to this frame. You know how you can rotate a radio sometimes and increase the signal? Once you've done that, tune the variable capacitor of your frame until you hear the signal increase in strength. You can also rotate the two together to maximize the signal. And that's what it does.
I don't know what's happening, but as I said in the other msg, I lost my program. This is the one one I said was "better".
Anyone who wants to add, subtract, or otherwise improve this msg is welcomed!
regards, Mike h