Jerry
Something really strange going on there. Do you have a different
crystal in the
same frequency range that could be substituted into the circuit?
Alternatively you might be able to build up a similar oscillator using
ugly-style
on a scrap of PCB and verify that your crystal can, or cannot, be
tuned. If you
don't reuse any L or C from the original circuit that would tell you if
the problem
is the crystal or one of the other components.
Since the IF filter crystals are the same frequency, it might be
possible to try one
of them in place of your present BFO crystal. Might prove something, or
might
not...?
The LC tuning mechanism can be changed from parallel to series, or
vice-versa,
to see if that makes a difference. My preference has always been to put
the L in
series with the C, and that in series with the crystal, but I have seen
it with the LC
network being parallel and that in series with the crystal. Both ways
usually seem
to work.
Arv
_._
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On 06/28/2013 10:49 AM, jerryk5lru wrote:
Arvid
I wound a 37-6 with fifty turns as per the calculator, worse. I
shorted the crystal and found I had moved lower to 6190. from the
8200. But still had the 135 KC tunable range with the crystal shorted.
I played with the coil until I got it to the 9995. range with the
crystal shorted and still had 135 KC tuning range, when I removed the
short it went back to just a 5HZ tuning range.
--- In BITX20@... <mailto:BITX20%40yahoogroups.com>, arv
<arvid.evans@...> wrote:
Jerry K5LRU
That indicates that your BFO oscillator should be tunable. Next step
would
be to check capacitor and inductor values to make it tune across the
crystal
frequency. You can change the inductor to a toroid core (T37-6
should work)
and adjust the turns until you get it to the right frequency. Toroid
calculator
located at <> can help with that task.
Arv K7HKL
_._
On 06/27/2013 10:59 PM, jerryk5lru wrote:
The crystal brand is KDS. I took your advice Arv and shorted the
crystal out and the frequency tuned from 8104. MHz to 8239. Mhz
105 KC
range. But way lower than the 9995. Mhz area. Jerry K5LRU
--- In BITX20@... <mailto:BITX20%40yahoogroups.com>
<mailto:BITX20%40yahoogroups.com>, arv
<arvid.evans@> wrote:
Jerry K5LRU
The LC network in series with the crystal (including series-C of
the two
feedback divider caps) needs to tune to the crystal frequency.
Tuning
this resonant network a bit above to a bit below the crystal
frequency
is what pulls it up or down.
I would check the resonance components associated with the crystal.
You might be able to get an idea of what is going on by temporarily
soldering a very short wire across the crystal to take it
out-of-circuit.
Then check the oscillator frequency. It should be close to the
crystal
frequency with the crystal shorted. Tuning range with the crystal
shorted will be more than with the crystal in-circuit, but this
will
tell
you if your tunable network really is tunable.
Arv K7HKL
_._
On 06/27/2013 12:02 PM, Paul Daulton wrote:
What type and brand of xtals are you using?
Paul k5wms
Quoting jerryk5lru :
This is a Bitx20 Version 3. I'm almost done with it. The receiver
receives good, the VFO bandwidth is between 14,000. and
14,450. The
exciter produces a signal of 500mv and the PA kicks that up to
around 4
volts. When trying to tune the BFO and the carrier balance is
where I
have the problem. My frequency is 9995.31 mhz at the emitter
of Q9.
Here is where the problem starts. Leonards instructions say I
should
have 15kc adjustment. But all I have is about 3 hertz, not
kilohertz
with the 22pf trimmer. So when I try to adjust the carrier
balance, in
transmit, 7 db down the filter skirt, I have no adjustment. The
carrier
balance is .321mv on the low side and .634mv on the high side. It
nulls
out in the middle of the pot. This is why I think I'm not getting
enough drive. Any thoughts? Thanks, Jerry K5LRU
Paul Daulton K5WMS
beacon WMS 185.302 khz qrss30/slow 24/7
Jacksonville,Ar 72076
em34wu
