Andy,
My understanding of British radio terminology is not complete, so I am a
little confused by your statement about the "receive" port of the
circulator.
In circulator (isolator) applications I am familiar with, the input of
the circulator connects directly to the transmitter output, the output
of the circulator connects to the TX input cavity of the duplexer, and a
50 ohm load is connected to the "side" connector. Once the three
capacitors (or six, on a dual circulator) have been adjusted on a
network analyzer with the loads that will be used in service, there
should be no reason to "tweak" any of the adjustments. In fact, I have
been able to improve the performance of a circulator that was originally
tuned with loads that were very close to 50 ohms, but was installed with
loads that were between 51 and 53 ohms. This is one tuning job that a
network analyzer can perform to a "gnat's eyelash!"
If you were able to improve your repeater's operation by "tweaking" the
circulator, I suggest that a better solution might be to tune your
antenna and/or your duplexer to 50 ohms. It might be an interesting
project to install a simple impedance matcher (Z-matcher) between the
duplexer and the antenna. It's not clear where each component in your
repeater system is installed, so perhaps you can elaborate on the
arrangement? Specifically, where is the circulator installed? Thanks!
73, Eric Lemmon WB6FLY
Andy Hearn wrote:
>
> HI
> I have just changed my 70 cm repeater antenna over to a co-linear 8
> dBd gain, was running 2 full wave dipoles stacked (reason..antenna
> faults and not able to mount with correct vertical spacing).
>
> When I was calibrating the circulator on the bench, all set up
> perfectly, with the receive port being sharp in its setting.
>
> On site since the antenna was running a slightly higher VSWR
> compared to a dummy load (1.2:1), I thought it might be an idea to
> just tweak the receive port to optimise the rejection. However I
> found the tuning to be very flat, question, is this normal or am I
> missing something?
> 73
> Andy G3UEQ
>
>
> Yahoo! Groups Links
>
>
>
>
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