December 12, 2012

20M VFO


7 comments:

wrhlamda said...
This comment has been removed by the author.
wrhlamda said...

ممكن معلومات اكثر عن مدى الانحراف وزمن الاستقرار ان امكن
وشكرا

ST2NH said...

Hello sorry for delay to reply - this VFO design from SSD book published by ARRL it is Hartley configuration derived by JEFT transistor and buffered by 2 PNP transistor Zener Diode is used to stabilized JEFT volt - Stability is good for DC RX - shielding and feed thorough cap are needed - tuning by surplus variable cap - good luck OM

ST2NH said...

Hi wrhLamda Your 40 M DC is so great project - The VFO you used is the same as mine _ i only used more steps to stabilized the frequency as I said shielding and feed through cap and a good Var cap - the stability of volt also is so important - use a good antenna for your test and select good time for the band to be open - enjoy listening

wrhlamda said...

thanks for your attention
I found the "Crystal Sets to Sideband" book at http://www.wa0itp.com/crystalsetsssb.html
chapter 10 have a good tip for making low drift VFO .
Now I'm trying make a stable VFO step by step , starting from power suply . M besine for power suply based on LT431 regulater .
it gave me good thermal stability so there is no change in power suply voltage even when I touch the regulator with the tip of soldering iron (less than 1mv).
also I try to run the VFO on low voltage(3v) to decrease the heat of the components .But that leads to very long warm up time (1.5 hr)
(5v ) gave me good result .
now I trying make some test with Capacitors and there thermal stability and (PTC)resister

wrhlamda said...

could you please if you can recommend me a good supplier for variable capacitor

ST2NH said...

look for old surplus RF equipments - Mine extracted from old valve tester.

RF PARTS have many option and prices range .

http://www.rfparts.com/caps_variabletuning.html