* Eric Lemmon <[EMAIL PROTECTED]> [2007 Jul 26 22:34 -0500]:
> Nate,
>
> Was the interference present before the duplexer was retuned?
Honestly, I don't know. It was "off the air" for some time most likely
due to the final transistor becoming unsoldered on one lead and the
controller being out to lunch. Also, I didn't monitor it to speak of
the past several years. So, this is almost like a new problem.
> If not, then
> I suspect that the tuning is not correct. Although I applaud your ingenuity
> in the duplexer tuning setup, a proper tuning of the notches on a BpBr
> duplexer really needs to be done on a spectrum analyzer or a network
> analyzer. The typical BpBr duplexer has a very broad peak that can be tuned
> precisely only with a network analyzer or a spectrum analyzer with a
> return-loss bridge. When tuned for return loss, the bandpass can be tuned
> with great precision. A network analyzer also has the advantage of
> presenting precise source and load impedances to the cavity being tuned,
> which makes it easy to tune them individually for cascade connection.
> Separate matching pads are not required with such an instrument; the match
> is built-in.
I suppose that stuff could be rented. <Goes through change in the
couch. Nope no spectrum analyzer fund there!> The other option is the
send it to the factory at the mercy of UPS...
Seriously, while doing it right is the best way, most of us don't have
access to that sort of equipment. We have an ancient IFR-1200 at the
shop that is too old to even put a tracking generator in (we've asked).
And for the price of the equipment above I could buy many other things
that would be far more satisfying including a down payment on a
countryside QTH, if one ever comes available. So, we use the SINAD
method.
Honestly, I don't know what the big deal is as the loss figures matched
the specs and we did nothing to disturb the coupling (I *won't* touch
that!). We can discuss impedances, but in the real world, there will
always be a difference between the test equipment and the devices that
are connected together on site. A lot of good information has come
from this thread as well as useful ideas. Thank you! But, shelling
out 5 to 6 Grand for a couple of dB improvement is not in my budget.
;-)
> How many cans are in your Wacom duplexer, and what diameter are they?
4, 8" most likely.
> You might find it useful to employ the interference calculation procedures
> found in GE Datafile Bulletin 10002-2:
>
> <www.repeater-builder.com/ge/datafile-bulletin/df-10002-02.pdf>
>
> Also download the interference analysis worksheet here:
>
> <www.repeater-builder.com/ge/datafile-bulletin/df-10002-03.pdf>
>
> The above documents were only recently added to the GE Master Index, and
> have great potential value in this instance. As for your original question,
> I believe that cable length between the additional bandpass cavity and the
> duplexer output should not be critical if proper tuning procedures are
> followed to ensure 50-ohm source and load impedances.
Thanks for the info Eric (and to everyone else as well).
Honestly, I expected a reply or two, but it's been fun to see everyone
run with this thing. :-)
73, de Nate >>
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