Rap 'n Tap
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From: Garry Nichols
Date: 11/15/00
Time: 3:43:19 PM
Remote Name: 209.4.255.69
Well Charlie, looks like the forum is working again!
To answer your questions, first, I was not describing an adjustment that would be for a single freq. Tuned loops (forgive me if I'm over-explaining) consist of the loop (1 or more turns) and a variable capacitor. If the loop has too much inductance due to size and/or turns, the highest freq it can be tuned to with the cap fully unmeshed will still be below the top of the BC band. It looked to me that your initial idea might function this way. So I suggested that you remove turns and adjust size (keeping what is left with as large an internal area as possible, i.e, one big turn will be more efficient than two smaller ones) so that it will tune to the top of the band with the cap fully unmeshed (lowest capacitance).
Since the loop itself will need to be continuously tuned, the var cap will have to be down at the listening area unless you tune it with a remote motor (too much trouble!). If possible, I would just run the ends of the loop wire down to the listening area and keep them relatively parallel and spaced a couple of inches apart. Home made parrallel feeders! Try not to lay them across substantial conducting surfaces or run them close to conducting masses. But don't sweat it.
If you decide to bring the conductors down, then you can decide how to couple to the loop. The simplest and maybe the best would be to put a diode on one side of the cap and then run that to one of the very high impedance primary transformers that Ben Tongue has been talking about. The other side of the transformer primary would go to the other cap terminal.
You could try just using high impedance phones and it will work, but the impedance match will not be optimum. You will loose selectivity and probably sensitivity too.
Your end fed wire sounds like the easiest deal to implement. Sounds like you can get a good enough amount of wire up. However, I would not use coax. Coax is for low impedance circuits which are relatively well matched. Just run the antenna wire directly to the set (that will add to the total length of your antenna) and run a ground wire to it also. Some of my sets work quite well without a ground.
73, Garry