Solid State VFO

[wb6kwt]

Someone mentioned using the NorCal FCC-1 as a counter and I have a question along those lines. How would you go about using the companion FCC-2 VFO with something like the Knight T-60? If you have any ideas I would be interested in knowing how you would do it. N4QA has been playing around with this idea but I don't think he has it working all that well.

Thanks,

Bob

[Carl WA1KPD]

Great question. I would love to build a stable VFO w/ Freq counter for the HT-9 and the HB 813 rig (to be) but am not technical enough on SS to do so

[John K5PRO]

I built a SS vfo for a DX100 last year, it was a disaster. I did a lot of work to shield it, and to stabilize it inside that central VFO box. When I turned on the high power, it either pulled, hummed, or caused all sorts of strange things. Because of the way it is driven in the DX100, the fundamental mode was terrible, i.e., using it direct on 75 meters or 40. When it was doubled or tripled, it was a little better. I had built a nice strong driver using a 2N5109 driving a step up torroid, to drive the driver grid. Even with healthy voltage there (like a tube would make) the DX100 threw fits and convulsions, did not want a piece of silicon inside there, no sir.

So out it came, and back went the toobes.

[steve_qix]

Hi !

I've built a successful solid state VFO - and a simple one at that!  Several other folks have also built this VFO, so I know it can be reproduced.  This VFO is what I now use all the time.

There are several things I did to make it stable.  The first, and probably most important thing was to run the oscillator at a HIGHER frequency than the desired transmit frequency.  For instance, my VFO runs at 7mHz and I divide it by 2 to get on 75, and by 4 to get on 160.  Of course, on 40 meters I'd have to use another frequency, or double a 75 meter oscillator.  It can be done, in any event, without too much trouble. 

By using a higher frequency and dividing, you can leave the oscillator running all the time, and not have a weak carrier "bleeding" through... and when you go to transmit, the VFO is already "warmed up" and on the correct frequency.  You don't get that typical DX-100-like drift (like old Irb always has) when one goes from receive to transmit.

If you want to see more, go to http://www.classeradio.org/vfo.htm

Regards,

Steve

[wb6kwt]

Steve,

I saw the VFO you built and it looks like it would be easy to build. I was thinking more of trying to use a DDS VFO. I already have a couple that work real well and can be programmed for different off-sets etc. I'm sure the signal from the DDS VFO will need to be amp'd up and maybe I can learn how to do that by looking at your circuit. Thanks for your input.

Bob

[steve_qix]

There are a few DDS vfos out there, although they can get a bit pricy.  Phase noise is, of course, the problem with any DDS.

I've fooled around with some DDS oscillator chips.  WAY too much phase noise.  Brent, W1IA bought a DDS kit from (somewhere) - I don't remember.  You could contact him and find out    I know ther phase noise is quite reasonable.

Regards,

Steve

[John K5PRO]

One more thing, if you do go to a DDS or other solid state VFO to drive a tube transmitter, be aware that you need some RF voltage, typically much more than a 0 or 10 dBm output. You can build a simple driver with a 2N5109, running off 15 volts or so, and use a step up transformer on the output. I built one for a friends DX60, and he is using it instead of the HG10 now. He has an S&S Engineering DDS box. Only problem was the feedthru carrier all the time, so he kills the driver voltage when receiving.