[Premium-Rx] Antenna Couplers

[Al Klase]

Hi Jim,

I I've owned and used a number of military couplers.  The
whole house is currently fed from a CU-1280 via 75-ohm TV
coax and fittings.  I'd don't have documentation for either
of the units I currently have, but I think I can provide
some useful info.  

For general SWL use, you can get away with passive splitters
for maybe two or four radios.  Keep in mind that you'll have
a 3db loss each time you do a 1:2 split only if you use a
proper hybrid.  The hybrid also provides about 30dB
isolation between outputs that keep the receivers from
bothering each other.  There's a good design detailed on my
website in the "SWL Antennas" systems section. To split four
ways you need three 1:2 couplers.

The antenna multicouplers are generally set up one of two
ways: (1) An amplifier, with enough gain to make up the
subsequent losses feeds an array of splitters. Maybe 1:8 or
even 1:16. (2) A low gain amp feeds a bus that drives an
array of emitter followers that drive the individual
outputs.

You have to keep in mind that the amplifier has to tolerate
EVERYTHING that come down from the antenna.  This typically
means a power amp with P1db in the 1-Watt+ range.  If you're
devoid of strong local signals you may be able to cheat on
the amp.

There's an Ulrich Rhode article in October 17 "Ham radio"
that should do the job nicely.  It's two 2N5109's in
push-pull with inductive feedback to preserve frequency
response, linearity, and noise figure.  You could probably
do this circuit with the same Amidon ferrite cores I specify
for the splitters.

Regards,
Al

"James C. Garland" wrote:
> 
> Does anyone have a circuit diagram of an active multicoupler? I'd like try
> and homebrew one, and don't want to reinvent the wheel.
> Thanks,
> Jim Garland W8ZR
> 
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-- 
Al Klase - N3FRQ
skywaves at bw.webex.net
Flemington, NJ 08822
Web Page:  http://www.webex.net/~skywaves/home.htm