Tim,
Yes, you can rent a spectrum analyzer- preferably with a return-loss
bridge, or you can borrow one.
Seriously, though, the duplexer is such a critical component in a
repeater system that you really should not try to cut corners on its
tuning. Once upon a time, I personally used some "creative" means to
tune duplexers, before I decided to acquire the proper test equipment,
and I always was able to improve on my prior work, using the proper test
equipment.
A spectrum analyzer with a tracking generator is the minimum essential
tool for tuning duplexers. However, not all spectrum analyzers are
accurate enough for such work, and fewer still have enough dynamic
range. Most low-end spectrum analyzers have an 80 dB dynamic range,
which is insufficient for duplexers that might have greater than 100 dB
of isolation. That's where a network analyzer really shines.
A return-loss bridge is an important accessory for a spectrum analyzer
(it's built-in to a network analyzer), since it allows you to tune for
an extremely sharp peak (actually, it's a sharp null) when tuning the
bandpass element, thus squeezing the nth degree of performance out of a
duplexer. A properly tuned duplexer should NEVER need to be tweaked at
the transmitter site. If tweaking a duplexer at the site does improve
either the reception or the power output, the chances are good that the
spectrum analyzer used to tune it is off frequency. It's also possible
that there is a significant impedance mismatch, but I don't want to beat
that dead horse!
I prefer to use a network analyzer to tune duplexers, because I can
easily verify that the jumper cables between cavities are the correct
length. In the case of your TX-RX duplexer, you probably should give
the factory a call to confirm the cable lengths for the model and
operating frequency. Depending upon your location, it may be
cost-effective to ship the duplexer to TX-RX, or to another vendor such
as EMR, for professional conversion and tuning to your repeater pair.
If you do this, do not let anyone touch the tuning controls after its
return!
The Bottom Line: Yes, you can tune a duplexer without any fancy
equipment- but why would you want to, if your objective is to have a
first-class repeater?
73, Eric Lemmon WB6FLY
timtarhanick wrote:
>
> I have a TXRX duplexer I am going to use on two meters. Everything I read,
> including the manual from TXRX states I need a spectrum analyzer for the
> tuning the duplexer. Is there any other way besides buying a spectrum
> analyzer to do the job?
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