--- On Wed, 11/25/09, W3ML <w...@arrl.net> wrote:
> From: W3ML <w...@arrl.net>
> Subject: [Repeater-Builder] pre-amp placement
> To: Repeater-Builder@yahoogroups.com
> Date: Wednesday, November 25, 2009, 10:46 PM
> Hi,
>
> I have now read two different things about where to put the
> pre-amp.
>
> One says before the Bandpass and one after.
>
> What I have now is the 6 can duplexer is hooked to the
> bandpass and then on the other side the pre-amp is connected
> and then a cable goes from preamp to radio.
>
> The other article I read this past week says the preamp
> should go between the cans and the bandpass.
>
> Which is right? Or does it matter?
>
> 73
> John
>
>
As always it is one of the "it depends" answer. You want the preamp as close
to the antenna as you can get it. This sets the noise figure or in simple
terms the minimal signal you can detect. Idealy it should be right at the
antenna. This is not possiable with a repeater and single antenna so you want
it right after the duplexer going to the receiver. Sometimes if you are in an
area with lots of transmitters that are overloading the receiver or causing
other problems (which is probably your case or you would not need the banpass
cavity) then the preamp goes between the banpass cavity and the receiver.
Most preamps do not have very much selectivity and many duplexers don't either
to signals outside the tuned frequencies. This lets the preamp amplify many
undesired signals and can cause all kinds of problems.
If your repeater is located very far away from other transmitters this is not
usaully a problem. If there are several transmitters near by then you may have
a problem without a band pass filter.
