On Tue, Aug 19, 2008 at 1:08 PM, John Transue <[EMAIL PROTECTED]> wrote:
> Members of Repeater Builder have been very helpful in my effort to improve
> the operation of a 440 repeater. The de-sense problem is reduced now by the
> addition of another cavity, a band pass cavity on the receive leg. Now I am
> wondering whether a circulator would provide additional isolation and
> further decrease the de-sense problem. Your advice would be much
> appreciated.
>
Circulators are mainly used as part of a TX multicoupling system where
multiple transmitters are combined to feed into a single antenna. They are
used to prevent the output from individual transmitters feeding back into
other transmitters on the same multicoupler. They are non-linear devices and
as such are always followed by a band-pass cavity (or cavities) to keep the
transmitted signal clean.
They may sometimes be of use where other nearby transmitters that are close in
frequency to yours (close enough and strong enough to get through your
duplexer band-pass filter) are mixing in the PA stage of your transmitter to
produce intermods.
They will have no effect on desense and will add another 1db or so insertion
loss. The best way to reduce desense in my experience is to use cavities that
have both band-pass and notch capabilties (I think TX/RX Systems call
them "Vari-notch" cavities). You tune the notch on the receive cavity to the
TX frequency and the notch on the TX cavity to the RX frequency. This only
works where you have reasonable separation between TX and RX e.g. at UHF. It
is not practical with less than a couple of MHz separation (IMHO).
> I have no idea where to get a circulator or what to expect it to cost. If
> you think a circulator would help, perhaps you can suggest sources and
> prices.
>
Honesly, in your situation I wouldn't bother (but that is just my opinion).
Regards,
--
===================================================
Rodney Baker VK5ZTV
[EMAIL PROTECTED]
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If someone had told me I would be Pope one day, I would have studied
harder.
-- Pope John Paul I
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