Hi all,
More investigation has narrowed the problem to the BPF/front end board
81593. We'll use 15 and 10 meters as our "working normally" and 12 meters
as "working abnormally" for this discussion:
- LO input from the XO-LO board at connector 26 is at exactly the right
appropriate frequency for a 9 MHz IF, and nearly constant voltage for
15/12/10 meters. That eliminates the XO-LO board as the problem (relief!).
- TX input at connector 27 is also nearly identical on 15/12/10 meters.
- However, the output at connector 24, which goes off to the low level
driver board, is not the same for all three.
Using a 1 Mohm input impedance on a Tek 2465A scope:
15, 10 meters: in TUNE mode, signal increases with PWR knob up to
about +/- 2V at three dots up from minimum (10:30 am clock position) and
then essentially saturates
12 meters: in TUNE mode, signal increases with PWR knob but only up to
about +/- 0.12V at three dots up from minimum and then essentially saturates
Not sure why the signal is saturating at the 10:30 am position as I would
have figured it would go up as I turned PWR up further. (It does go up to
a clean 90 watts or so on 15 and 12 meters when everything is hooked back
together.) No matter; the problem is clearly in low output at 12 meters
from 81593.
Since 81593 has individual BPFs for each band that are used for both TX
and RX, my guess is that the BPF is off frequency for 12 meters which would
explain why I have a relatively deaf receiver by 20 dB on that band as well
as low TX output.
Now the next question to this group: does anyone have the alignment
procedure for a 81593 BPF/front end board? The manual does not describe
one. I am also very careful about adjusting slugs as like many of you,
I've had inductor cores snap in two with too much pressure, so I want to do
the minimal amount of tweaking to fix the problem and not do too much
"golden screwdriver" wiggling back and forth. Knowing what to inject and
where to inject it would be great. (I have HP signal generators and the
like available.)
This list is really terrific - and thanks to Gary W0DVN and Pete in
particular!
73
Phil W1PJE
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