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[SSDN] Putting a Real LC VFO in My Ceramic-Resonator, Direct Conversion 40 Meter Receiver. LC JOVO! (Video)

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SSDN via rec.radio.amateur.moderated Admin

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Jul 19, 2022, 12:27:07 PM7/19/22
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Putting a Real LC VFO in My Ceramic-Resonator, Direct Conversion 40 Meter
Receiver. LC JOVO! (Video)

Posted: 19 Jul 2022 04:03 AM PDT
http://soldersmoke.blogspot.com/2022/07/putting-real-lc-vfo-in-my-ceramic.html


This is the DC receiver that I built back in 2017-2018. I had used a
ceramic resonator in the VFO. That receiver was on the cover of SPRAT
magazine. It may not have deserved the honor -- recently Dean KK4DAS and I
discovered that the ceramic resonator VFO drifted rather badly. So Dean
and I are now building real LC analog VFOs. This is kind of an aside to a
Virginia Wireless Society -- Maker Group project. This video shows my
receiver working yesterday on 40 using the VFO that was recently thrown
together.
More details on the original project (that used the ceramic resonator)
here: https://soldersmoke.blogspot.com/search/label/DC%20Receiver%20Build
The VFO circuit comes largely from W1FB's Design Notebook page 36. I
followed most of the conventional tribal wisdom on VFOs: NP0 caps, often
many of them in parallel. Air core coil (in my case wound on a cardboard
coat hanger tube).
For C1 I used a big variable cap (with anti-backlash gears) that Pete N6QW
advised me to buy on e-bay. Thanks Pete. L1 is on the cardboard tube. I
only built the oscillator and the buffer -- I did not need the Q3
amplifier. (The water stain in the upper left is the result of a heavy
rain in the Azores around 2002 -- water came pouting into the shack.)
I think the VFO is more stable than the Ceramic Resonator circuit. But I
want to go back and give the ceramic resonator circuit another chance...
Miguel PY2OHH has some really interesting ceramic resonator circuits on his
site. Scroll down for the English translation:
https://www.qsl.net/py2ohh/trx/vxo40e80/vxo40e80.htm
Dean KK4DAS commented that VFO construction is as much an art as a
science. I agree -- there is a lot of cut and try, a lot of fitting the
components you have on hand into the device you want to end up with. You
have move both the frequency of the VFO AND the tuning range of the VFO.
Mechanics (in the form of reduction drives) is often involved. And, of
course you have to apply lots of tribal knowledge to get the thing stable.
You could, of course, avoid all of this by using an Si5351, but I think
that moves you away from the physics of the device, and is just less
satisfying.
So, JOVO! LC JOVO! The Joy of VARIABLE Oscillation!

wb0...@gmail.com

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Aug 9, 2022, 11:40:09 AM8/9/22
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And the agony of an oscillator that demands to be an amplifier instead! :-p
Bob WB0POQ
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