> I have been pulling my hair out (I don't have that much more
> to go) over an
> old Celwave 6 cavity 526-4 pass reject duplexer. I can get
> the notches to
> tune properly one by one but when I put it all back together
> it just does
> not seem to sum out right. Is there a procedure someone can
> point me to?
526's usually tune up pretty straightforward. If it's an older 526, it may
have RG-8 interconnects, which can get noisy (better to replace with RG214).
As far as tuning the notches, they are generally a PITA to tune to begin
with due to the mechanical design (almost as much fun as Motorola T1504's),
but as far as tuning them up separately and then putting it back together
and having it not work right, I can't say that I've seen that effect, but
then again, that's not how I would tune it. You can get in the ballpark by
doing it that way, but in the end, you'll need to look at return loss to
know when the pass is really tuned right, and you may need additional
amplification to really see the notches, since when it's properly tuned,
notch depth will be over 100 dB (although if yours has RG8 interconnects,
you may not realize that kind of notch depth). In fact, if yours has RG8,
it wouldn't suprise me if some of the problems you're fighting are related
to cable leakage coupling.
Just to confirm, the one you've got was the 440-470 split model, right? If
not, then the cable lengths will be wrong and you can expect to see problems
like you're experiencing (notches won't "line up", insertion loss high,
etc.).
As always, isolate your test equipment from the DUT with pads when tuning.
> Also, I am curious if I need to use the same high frequency and low
> frequency ports which would be the opposite for ham radio out
> here, or if I
> need to keep the transmitter port for the transmitter and the
> receiver for
> the receiver.
The 526 is symmetrical - you can use either side for high pass or low pass.
--- Jeff
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