NADER's Satellite Blog: 20M VFO

December 12, 2012

20M VFO

7 comments:

wrhlamda said...: This comment has been removed by the author.; December 12, 2012 at 10:40 PM
wrhlamda said...: ممكن معلومات اكثر عن مدى الانحراف وزمن الاستقرار ان امكن
وشكرا; December 19, 2012 at 7:49 PM
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; December 20, 2012 at 12:53 AM
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; December 20, 2012 at 2:06 AM
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; December 20, 2012 at 7:02 PM
wrhlamda said...: could you please if you can recommend me a good supplier for variable capacitor; December 20, 2012 at 8:05 PM
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; December 21, 2012 at 3:13 PM

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