5447Re: [loopantennas] Re: Remote tuning
- Aug 1, 2008
>I remotely tune my receiving loops with varactors. The tuning voltage is also the amplifier supply voltage, and the amplifier is designed to work with the varying supply voltage.
> > So, it occurred to me that it would be good to come up with a cheap
> > and easy way to turn a tuning capacitor <snip>
> That's basiclly a good idea and it's probably workable if the 180
> degree mod can be done with a servo powerful enough to turn the cap.
> The small tuning caps from cheap radios are usable in loops and turn
> easily. But these days remote tuning is usually done with a varactor
> diode. This replaces the cap and is tuned by a DC bias across it.
> This variable voltage is usually sent up the signal feedline, isolated
> by capacitors. Other posters on this forum have given links to examples
> of this. The servo would, however, be a good way to rotate the loop.
> You can find circuits on the web to operate the servo directly without
> the R/C stuff.
I'm going to be working on a remotely tuned transmitting loop where the motor is controlled with the DC voltage going up the coax. Using a variable capacitor without a stop pin on the shaft relieves me of the trouble of having to add stop switches and diodes.
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