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The decision whether (or
not) to add a preamp to the receive side of a repeater should be made after
carefully evaluating your installation. As many others have preached
(besides me!), a receive preamp is *not* a cure-all; indeed, it may create new
problems rather than solving old problems.
First of all, your
antenna should be the optimum design for your station, balancing gain and
pattern with "duplexability." The highest-gain antenna available is not
always the best choice, especially if the repeater site is at a high
elevation. Downtilt antennas have very "spoky" patterns, and should be
evaluated very carefully.
Your feedline should be
as good as, and as low-loss as, you can afford. My rule of thumb is to
*always* select a feedline that has no more than 1.0 dB of attenuation at the
receive frequency. Don't be compelled to put your antenna at the 500 foot
level of a tower, simply because the tower is 500 feet tall. Five hundred
feet of too-small feedline can have a *lot* of loss, and it's possible that the
repeater will work far better just 50 feet above ground.
As Chip Angle has pointed
out in his excellent application notes, a receive preamp should *always* be
preceded by an effective bandpass cavity filter. Such a filter not only
greatly attenuates your repeater's transmitter carrier, but it also keeps out
all of the other carriers that can desense your receiver. Go
here:
A notch-only duplexer is
perhaps not the best choice for a repeater- especially in a high-RF
environment.
73, Eric Lemmon WB6FLY
From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Tuesday, January 17, 2006 9:10 AM To: [email protected] Subject: [Repeater-Builder] Repeater Receive Preamp Interested in the idea of placing a preamp on the Rx side to increase HT
coverage. I've read in an article they should not be used with
Notch-Reject Duplexers though...we have one. Thoughts were to place it in
the line between the duplexer and Rx radio on a duplexed, single antenna
repeater setup. Any successes or failures with using a preamp w/ this type
of
duplexer?
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