[AMRadio] Re: Top Band


Todd, KA1KAQ ka1kaq at gmail.com
Tue Sep 4 13:54:30 EDT 2007


On 9/4/07, D. Chester <k4kyv at charter.net> wrote:

> Rather than having a crystal ground for the popular AM frequencies, why not
> control it with a VFO?  It is easy enough to convert the crystal oscillator
> stage to VFO control by bypassing the control grid to ground (either
> directly or through a capacitor, depending on whether or not any bias is
> applied at the control grid.  Usually there is an rf choke between the
> cathode and ground, with a feedback circuit back to the crystal.  Disconnect
> the feedback circuit from cathode and apply the VFO signal there.  The VFO
> signal needs to be  low impedance, 50-250 ohms, and about 1/4 watt will
> usually do the trick.

You bring up an interesting point, Don. I have Barry Wiseman's old
300G nearly ready for primetime, so I find it particularly
interesting. He did include a cable made to fit into one of the 40F
crystal oscillator boxes, but it isn't terribly long. I'm not sure
where he mounted the VFO, perhaps inside the cabinet behind the door?

For me, it would be far more advantageous to have the VFO mounted
remotely. Not far away, but outside the transmitter box itself and on
the operating table next to it. A fuzzy memory tells me that long VFO
cables, even shielded, are not a good idea. How long is 'too long'?

Barring that, the unit has two crystal oscillator boxes, each one can
hold a different rock and notes can be made of tuning positions for
each. With another winter in Vermont looking more like reality, the
160 ant will go up.

~ Todd,  KA1KAQ


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