> 1. Do the low side tuning rods (3 cavities) affect the high
> side tuning
> (3 cavities)?
Very little, if any.
> 2. Since there is no way to use (or measure) just one cavity section
> (they are hardwired together), how does the tuning of one rod
> affect the
> others? Do you just start the adjustment from one cavity and
> then move
> to the next?
Basically, yes. Do you have sweep equipment (tracking generator/spectrum
analyzer) or network analyzer? If so, the tuning will be very obvious. If
not, you will at least a signal source (sig gen) and receiver (spectrum
analyzer, well-shielded receiver, etc.). Keep in mind that even if the
duplexer says "Tx" and "Rx" on the ports that if you are using a
Northeastern inverted pair (i.e. Tx 446, Rx 441) that you will be using them
opposite of how they are labeled.
Generally speaking, here's a quick outline of the tuning. Don't worry, it's
pretty hard to screw up tuning notch duplexers. I'm giving you the simple
version - no patch cable swapping involved.
I'm going to assume that your Tx is 441 and Rx is 446. You'll need to make
the appopriate changes if this is not the case. Of course, all of the usual
caveats apply: use double-shielded test cables, a high return loss
termination, quality 6 or 10 dB pads on the sig gen and receiver for
isolation, etc.
1. Hook up the sig gen to the port labeled "Tx" or "low pass". Hook up the
receiver/detector to the "Rx" or "high pass" port. Terminate the antenna
port with a good load.
2. Generate a signal at the 441 Tx frequency (and likewise tune the
receiver for the same). Tune the slugs on the "high pass" or "Rx" side of
the duplexer for minimum signal (maximum notch), increasing the signal
generator output as necessary for an on-scale reading if using a receiver
with an S-meter. You will be screwing the slugs inward to go lower in
frequency from where the duplexer was originally tuned. Since you're moving
> 20 MHz from where they were originally tuned, you'll be cranking in quite
a ways...
3. Generate a signal at the 446 Rx frequency (and tune receiver for same).
Tune the slugs on the "low pass" or "Tx" side side for maximum notch.
4. Repeat steps 2 and 3 one time for good measure.
You should have at least as much isolation as the specs call for. If you're
very careful in your tuning, you should be able to significantly exceed the
spec's notch deptch. Insertion loss should be right at spec, maybe 0.1 or
0.2 dB below if you're lucky.
> 3. Can you mis-adjust the unit such that you seem to have a notch at
> the right point, but in fact there is a better adjustment point?
Provided that the notch depth meets spec, the answer is no, it's not
possible if the duplexer is working right (i.e. hasn't been damaged). There
is only one notch "dip" per resonator, unlike some pass/reject duplexers
which show a "dual notch" response (typical of many full-size cavity
resonators that have a single loop with a series reactance to ground).
> 4. Can or how do you adjust or affect the 5 MHz split? Or
> is each side
> (Low vs High) independently adjusted?
They're independent.
> Thanks for your time,
> Marc
> W1MBT Trustee
If this is your first shot at tuning a duplexer, you probably couldn't pick
an easier one than a UHF notch-only flatpack, so consider yourself lucky!
---
Jeff
--------------------------------------------
Jeff DePolo WN3A - [EMAIL PROTECTED]
Broadcast and Communications Consultant
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