And let's do the math for the failure mode:

20 dB isolation in the receive mode, which is also the transmit failure mode.

20 dB is a voltage ratio of 10:1.

A 10 watt transmitter will put 22 volts RMS (32 volts peak) onto a 50 ohm line.

The receiver, 20 dB down, will see 3.2 volts of RF peak at its input IF the
input is purely resistive. All bets are off if there is a reactive component.

The little balancing resistor used in the Wilkinson hybrid in that device is a
quarter-watt resistor as I recall. Dumping 10 watts into it will frenchfry it
in less than a second, and THEN what is the isolation specification?

I don't know many base-emitter junctions that can take 3.2 volts and stay glued
together. Same for protection circuits at the input...100 milliwatts of RF is
pretty close to the dissipation limit of most devices used in light aircraft
radios.

$600 for two quarter-wave sections of coax, two reed relays, three BNC
connectors, and a metal box is a hell of a way to make a living.

Just some thoughts, mindya.

Jim





Rob Cherney
shared these priceless pearls of wisdom:

-On Fri, 11 Jun 2004 07:02:03 -0400, "Nicholas J. Hirsch"
wrote:
-
-Is there a solution for this such as a combiner or RF
-switch that can be used with 2 aircraft radios?
-
-Yes, but it's not cheap (~$680). See:
-
-http://www.comant.com/htmls/ci601.html
-
-Rob-
-
-------------------------------------------------------------------
-Robert Cherney e-mail: rcherney(at)comcast(dot)net

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com