Ron,
????????Reminds me
of the old days as a youngster building Valve VFO, enclosing it in a box
etc.. For PSK: I suggest that you take this requirement to the another
extreme and build a DDS VFO !!! Not Joking, its actually the best of both
worlds.. Its tough to make a VFO with 10Hz stability.
????????Try
replacing the 56pf next to Q5 with polystyrene.. it should give your
major improvement.
????????No recent
experience with digital. I used to run a bbs till some years
ago..
73 Raj vu2zap
At 03/02/2005, you wrote:
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I really appreciate your quick
reply Raj,
No you did not confuse me.
This forum is alive
!
Yes I used the ceramic ones for initial trails. I have some polysterene
ones (old!! from Philips radios) in my junkbox and will do some trials
coming days.
What is your feeling about making the 2 transistor vfo as shown in the
original schematics working with a freq. drift of 10Hz or less (this is a
tough requirement for digimodes like psk31).
Is there experience with the bitx working with digimodes (rtty, psk31...)
as far as you know?
?
73 and again tnx fer advice!
Ron
Raj wrote:
- Ron,
- ???????? This is probably
because of ceramic capacitors being used the
- oscillator stages. Components that determine frequency must be
ultra-stabe.
- Use NP0 caps, brown ceramics with a black top. You can also use
- polystyrene, they are transparent plastic with a silver foil visible
- inside. They were only available in the old days in small pF values
less
- than 5Kpf.
- ???????? I usually pour bees
wax on top of oscillator components to keep
- them thermally isolated and keep them from shaking.
- ???????? Avoid ceramic caps
in audio stages, it causes microphonics. Tap
- them and you will hear a thump in the speaker/transmission. Use
- mylar/polyester.
- ???????? Do not use
mylar/polyester type caps in RF stages for bypass,
- instead use ceramic. Polyester work well in audio for
coupling.
- ???????? Ceramic = brown
round disks
- ???????? Polyester/Mylar =
green like a chewing gum with leads.
- ???????? Hope I have not
confused you..
- 73 Raj
- vu2zap
- >MHz IF will give the proper range) Frequency range seems to be ok
but
- >stability is bad. After 20 minutes waiting freq shift of 1 KHz
still
- >exists. I think I will order some components for a
HuffAndPuff
- >circuit for stabilizing purposes.
