Doug,
It is a characteristic of BpBr (bandpass/bandreject) duplexers that the "pass"
function is very broad while the "reject" notch is extremely sharp. While it is
true that a 15 kHz shift will probably not be noticed on the pass, it *might* be
significant on the notch. It takes a network analyzer, or a tracking spectrum
analyzer with a return-loss bridge, to accurately set the pass tuning. The
notch
is relatively easy to tune- just tune for minimum signal at the reject
frequency.
Another characteristic of BpBr duplexers is that adjustment of the threaded
tuning rod moves both the pass and the notch in unison, while adjustment of the
notch capacitor moves only the notch. Therefore, you should NOT touch the
capacitor. Simply tune the threaded rod while watching the notch on a spectrum
analyzer or RF millivoltmeter for minimum signal at the notch frequency. It may
be a good idea to tune each cavity individually. Keep in mind that 15 kHz is a
very small shift, so the movement of the threaded rod may be very small- perhaps
1/8 of a turn or less. On a TX-RX duplexer, maybe much less.
I tend to agree with other posters who suggest that you could probably use the
duplexer as-is. A 15 kHz shift is a pretty small change, and the tuning should
be attempted only with test equipment that is known to be exactly on frequency
or
is slaved to a frequency standard.
73, Eric Lemmon WB6FLY
doug wrote:
> well, we are going to try this method:
>
> first, we are going to try the unit "as is" and pay close attention to rx
> sensitivity and swr.
>
> second, we'll retune the notches (this was recommended by mary brown @ tx/rx)
>
> third, they go back in a box for a trip back to mama (tx/rx)
>
> i'll keep everyone posted.
>
> doug
>
>
> Yahoo! Groups Links
>
>
>
>
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