Eric / Don
Mine is a 3 port Circulator/isolator, I tuned it up on sig gen with
50 ohm pads and UHF rx with 50 ohm pads as detector, rotating it
round a few times to optimise receive port isolation, I was getting
around 65 dB isolation between TX port (1) and RX port (3), insertion
lost TX port (1) to antennae port (2) less than 0.5db, ant port (2)
to rx port (3) less than 0.5db..happy with that, as I said it works
well, but just wondered why on site tuning was flat.
I appreciate the traditional way the unit works as you have
described, I would like to try your way but my shift here is 1.6MHz
and I do not have a duplexer for that sort of spacing ( although
after the isolator, my cavs do a good job.
Also Don, appreciate offer, but do have test gear at home to do it
in passive mode so to speak.
rgds
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
> >
> >
> >
> >
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/Repeater-Builder/
<*> To unsubscribe from this group, send an email to:
[EMAIL PROTECTED]
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
