[AMRadio] VFO for 20V-3

Jim Candela jcandela at prodigy.net
Sat Dec 24 09:10:05 EST 2005


   Contact WA1FFL about his DDS VFO Kit. This was in
QST back in 2001.


I built one here, and although not complete, it works
very well. I opted for 2.5 to 12.5 Mhz tuning range,
but you can select from several options such as 3.5 to
4.0 Mhz.

With a simple 1 transistor amplifier (MR4134 T-Mos
FET), I get 20 Volts P-P into a 220 ohm load. The
output is a sine wave without any L-C filtering. With
a cheap 50.0 Mhz crystal, my VFO is only 20 hertz off
from the dial (plus offset) setting.

One downside is the display reads from the low end,
and not the actual frequency. You can save money and
forget the display, and instead use a digital
frequency counter. Another issue is that every time
you power up, the frequency reverts to the bottom of
the range. These are only minor annoyances offset by a
clean and rock solid VFO.  

I'm still waiting on putting it all in a cabinet, and
hooking it to my 20A.


--- Bob Maser <bmaser at tampabay.rr.com> wrote:

> After messing around with some "Ham" crystals and
> getting low oscillator 
> output, I have decided to find a suitable VFO for
> the 20V-3.  Some time back 
> I saw a posting on this reflector for a modern VFO
> that some ham was 
> selling.  Does anyone have this info?  What other
> VFO's would work, like 
> Heath, Johnson, etc.?
> Thanks,
> Bob Maser
> W6TR 
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