Jed,
Check with Telewave for good prices for Hams, usually 30% off of the list
price shown on their Web site www.telewave.com. I believe that TX-RX also
has a Ham discount schedule. You're looking at $250-400 for a single
isolator and $550-700 for a double isolator. You can also buy them retail
at TESSCO and Talley, two distributors who cater to commercial radio and
cellular operators.
Whether you should use a single or a double isolator depends a lot on
whether your repeaters are commercial-grade or Amateur-grade. A single
isolator is always a good idea, since it will protect the PA from
destruction if the SWR increases due to an antenna or feedline problem.
This is more of a problem at UHF than at 220. That's why Motorola UHF
transmitters at the Quantar or MTR2000 level always come with a ferrite
isolator as standard equipment. Amateur-grade transmitters from Ramsey,
Hamtronics, Maggiore, etc., do not come with an isolator, and are very
vulnerable to failure if the load impedance is not stable.
The term "circulator" really refers to the three-port ferrite device
itself, and a circulator becomes an "isolator" when it comes with a dummy
load already attached to the third (load) port. If you plan on using your
own dummy load on a new circulator, you should send that dummy load to the
vendor so that the circulator can be properly tuned. Due to the variation
in impedance and return loss between individual dummy loads, it is never a
good idea to change the load(s) after an isolator is properly tuned.
I recommend using at least a single isolator for PA protection at sites
that have very low intermodulation interference potential, but a double
isolator at sites with significant IM potential. Some site managers won't
even allow a transmitter on the premises without a dual isolator followed
by a low-pass and/or a cavity filter. Choose wisely...
73, Eric Lemmon WB6FLY
Jed Barton wrote:
> Hey gang,
> I'm putting a 220 and 440 repeater at the same site. I'm running Wacom
> duplexers on each machine. Any suggestions on where to get circulators,
> and how much we're talking in terms of price? Thoughts? Each machine
> is 100 watts.
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