Howard, there are a couple of things to keep in mind on installing a preamp:
1. The losses in the duplexer and feedline cannot be made up in a preamp placed
at the receiver input. You can increase the receiver gain with a preamp, but
those losses are not recoverable.
2. You want to place the preamp at the output of the duplexer and put the
attenuator between the preamp and the receiver. If you have a good preamp with
a high level intercept point, you can usually gain a few dB if the repeater
receiver is not as sensitive as it could be.
Sensitivities in the order of .35 uV for 12 dB SINAD are common and they can be
improved with a preamp, but if you are already using a receiver with .15 or so
sensitivity, you will not be able to see any improvement by adding a preamp.
In fact, it is quite possible to decrease the sensitivity due to overload in
the preamp.
Do a test on the repeater receiver to see what it's sensitivity is at present
and compare to the figures given above to see if a preamp can add any useful
sensitivity to the system. Often you can gain some sensitivity by using an
Iso-Tee at the antenna port of the duplexer to inject the signal generator and
tune the receiver front end through the duplexer thus compensating for any
reactance in the duplexer. Using a SINAD test and tuning for best quieting
will often result in improved sensitivity over using a meter on the first
limiter to tune up the receiver.
Hope this helps -
73 - Jim W5ZIT
Howard <[EMAIL PROTECTED]> wrote: Hello to all and
thanks for reading.
I am in the market for a preamp for my 2 Meter repeater. I am not
looking to invite intermod so am asking for suggestions on what to
buy. I am only looking to compensate for losses in feedline-cavities
so huge gain is not required. As a matter of fact, I am assuming I
will have to use an attenuator in front of the preamp.
Anyway, any advice on a brand/model of preamp you have used
successfully greatly appreciated.
73 de W2AFD Howard
_
