With idea of a VFO that can do 3 - 7 and 7 - 20, how about making a really
stable VFO at the 3 - 6 range and switch in a doubler circuit for the
higher range? Don't know if that would be good enough but it's just a
thought.
I've built VFOs with a temperature compensation circuit that worked well if
you adjusted it carefully. Really nothing more than a high negative
coefficient cap and a high positive coefficient cap fed to a differential
capacitor in the tank circuit. Tune for minimum drift. Used to test it
using "Circuit Freeze" when that was available.
I also have a couple of Atlas rigs too and they (mine) were surprisingly
stable.
Bob WA2EGP
On Sat, Apr 1, 2017 at 6:50 PM allison <ajp166@xxxxxxxxxxx> wrote:
Lately I have been playing with Atlas 210X traceivers and they use
switched frequency VFOs
with the 10M range going to 23mhz. With good temperature compensation
they are
amazingly stable. Granted many made it from the factory with poor
temperature compensation
but I have two that will hold within 100hz an hour after 10 minutes at
room temperature.
*From:* Ashhar Farhan
*Sent:* Friday, March 31, 2017 11:24 AM
*To:* minima@xxxxxxxxxxxxx
*Subject:* [minima] Re: Finally getting around to building my Minima...
A simpler scheme than the Si570 is to use a lower frequency IF like 11
MHz.
Make a solid JFET VFO in a shielded box that has two sections, one that
goes from 3 MHz to 7 MHz, the other that goes from 7 MHz to 20 MHz. Then,
just add a very simple Huff and Puff.
This scheme may look basic, it is not. The phase noise of such a system
will beat the best of the radios on the market.
It is not exactly easy either. First, you need a very nice tuning
capacitor with slow motion drive. Next, you will need good mechanical
skills to build the VFO.
- f
Ob
