On Mon, 23 Mar 2009 19:32:44 -0700 (PDT), Jim Murray wrote:
>When bringing in a receive antenna to two receivers is it
necessary to have some kind of splitter with isolation?
There are two reasons why one might want a passive splitter with
isolation. First, and least important, is impedance matching.
Second, and most important, is leakage of an oscillator from box
to the other.
An excellent company based in Brooklyn, Mini-Circuits Labs, makes
very good passive splitters that do exactly what you want. The
ZFSC-2-1W is a 2-way splitter that is specified for a minimum of
20dB isolation (30 dB typical) from 1 MHz to 750 MHz. The ZFSC-2-4
is a 4-way splitter that covers 0.2-1,000 MHz with about 10dB less
isolation. With both splitters, the loss is about 0.5dB greater
than theoretical (3dB for 2-way, 6dB for 4-way).
Splitting loss matters ONLY if the circuit noise in the receiver
is greater than band noise. Thanks to static from thunderstorms
and other manmade noise, that never happens on 160M. As W8JI
suggests, if the noise increases when you connect your antenna,
you have enough signal.
I've used Mini-Circuits splitters for nearly 30 years with the
professional wireless microphone systems that I design for major
performance venues. I've got one of them in line between my
Beverages and my K3s.
www.minicircuits.com
73,
Jim Brown K9YC
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