J Shrum wrote:

I was curious if anyone has had any experience w/ homebrewing the PTO/VFO
from
http://www.qrpp-i.com/projects/ka8ma...-schematic.gif
.

I am pretty new to homebrewing, and was wondering if anyone knew of any
problems w/ this design that I may watch for. I have read that VFO's can be
very tricky, but this one looks incredibly simple. I'm just looking for
anyway to get out from under the rock that I'm bound to.

Thanks for any input...

James Shrum - KC9FFX



It's not that they're tricky to look at -- it's that they're tricky to
get everything working right.

This looks like it's a basically good design. It's common-source, which
is a bit odd. There's no buffer indicated, which will be necessary.
Really what makes VFO construction difficult is getting the thing stable
with respect to nearly every effect in the known universe, and that has
more to do with component selection and construction methods than it
does with the schematic.

If I were going to recommend a VFO I'd recommend a series-tuned
colpitts. You can probably find one in the ARRL handbook and build
away. If the designs look complicated it's because to be useful a VFO
needs the oscillator itself, a buffer amp and usually a power amp. The
schematic you have leaves off the buffer and power amplifiers; by the
time you stick those on your schematic will be as complex as any other
VFO design you've seen.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com