Hi Larry;
I have two sets of 70cm cavities. Each set is comprised of four
independent cavities (approx. 4" diam. x 7.5" high). I don't see a
model number on any of them. One set is made by Phelps-Dodge; and I
am told that the other ("Vari-notch") set was made by Cell-wave. The
Phelps-Dodge cavities have built-in type N connectors; but the
Cell-wave cavities have BNC connectors on a block on the top, near
what I believe is the notch adjustment (?). Because of the high-noise
environment that the repeater will be in, I am planning to use the
four Phelps-Dodge cavities (in series) for the Rx side of my duplexer;
and two (of the four) Cell-wave cavities for the Tx side of the duplexer.
I'm told that when I make up the cables for these, I need to include
the length of a "loop" inside; but I am still trying to determine how
to do that. That aside, I'm not sure if these "loops" that are being
referred to for the length measurement are the same ones that you are
referring to as well. I was only aware of bandwidth and notch
adjustments on these cavities (i.e., not a specific impedance
adjustments as well).
Once I make up the cables, then I get back to the task of trying to
tune them up. I guess that I could throw money at the problem or try
to get someone else to do it for me; but I'd like to be able to do it
myself. I could also rent a tracking generator or network analyser
(as you suggested); but I suspect that "renting a technician to run
it" is illegal in this state ;-) . Kidding aside,... as I said, I'd
like to get to where I can tune these things myself. So if it can be
done with what I have access to, I'd prefer to do so; even if it takes
me a bit longer. I was under the impression that I could, if I get
the test setup and procedure correct.
Alternatively, I guess that I could try to sell my Wavetek 1080, and
use the money to go toward a tracking generator, network analyzer, or
whatever else is usable; but I haven't looked into that option much
yet. In the mean-time, I was trying to get it done with what I have.
> > Which post (from Gary) are you referring to; and what
> > specifically should I be paying special attention to?
>
> His post dated 4/1/07 at 9:21 pm. He starts out "Duplexer
> and cavities have been tuned for many years..." Excellent
> post - one of the best I've ever read.
>
Now that I know what to look for, I'll go read the message you indicated.
Albeit, I am reluctant to throw money at the problem or have someone
else do it for me, I do appreciate all your advice.
Thank-you.
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