Re: 4S QRP Watering Holes!
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I've been following this and the Pig Rig thread. I seems that there are some concerns over being pinned down to one frequency, and it may be that there will be some VXO modifications that will arrive in due time. There are some well-known techniques for stretching the frequency swing a small bit, e.g., paralleling a second crystal of almost the same frequency and putting one or more inductors in the pulling circuitry.
Of possible interest is an article published in 73 Magazine for March 1996 by Ken Cornell, W2IMB, SK.
The link is:
Ken used that simplest of oscillators, the Pierce; An MF102, one crystal, five disc capacitors , one resistor, one rf choke and a permeability tuned inductor. Ken reports being able to swing a 3.57945 mHz color burst crystal some 30 to 40kHz! The secret was in the sauce and the sauce used litz wire in the inductor.
My workbench is currently bare for I am presently concerned with post-Sandy repairs and clean-up, but I find myself not too charmed by the mechanics of the described permeability tuning arrangement.
I'm wondering if the inductor might be litz wire on a toroidal form with the variable tuning supplied by a variable capacitor. Another thought is that, instead of a variable capacitor, a control winding might be interwound with the litz, and that control winding could be shunted by a rheostat. Varying the rheostat's resistance would vary the impedance that the control winding would reflect back into the litz winding, and thus change its inductance and the oscillator's frequency.
To: 4sqrp@...; davemrtn@...
CC: wa0itp@...; jomatlock@...
Date: Sat, 2 Mar 2013 05:24:47 -0600
Subject: Re: [4sqrp] 4S QRP Watering Holes!
Putting the pigrig on 7122 might be super easy, but what happens when you have to move up or down a little when that frequency is busy?
On 03/01/2013 10:19 PM, David Martin wrote: