--- On Wed, 2/4/09, Ralph S. Turk <w7...@comcast.net> wrote:
From: Ralph S. Turk <w7...@comcast.net>
Subject: Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or
Advanced Research Preamp
To: Repeater-Builder@yahoogroups.com
Date: Wednesday, February 4, 2009, 9:11 PM
#yiv258189647 p {margin:0;}
Hi Bob
All duplexers have very poor out of band attenuation. The extra cavity is to
narrow the bandwidth.
Cavity should have 2-3db of insertion loss (equates to sharp slopes).
Preamp gain is adjusted by use of a step attenuator. Determine how much attn
is needed to just raise
the limiter by about 10% max. This way you make up for loss of system plus
about 10%. Too much gain will
just lead to overload of the front end of the RX.
Ralph
Most do have the poor out of band rejection. Years ago I was involved with a
repeater that had a 4 cavity 2 meter Wacom duplexer . It had all kinds of
intermod. Must have been 100 transmitters within about a 10 block radius.
Shipped it to Wacom and had them add a pass cavity to each side. Worked fine
then. I think after that they offered one that way in their catalog.
