[Premium-Rx] Racal 6790 T-R switching

[Carcia, Frank A. HS]

	Hi All,
	I use a RA6830 all the time with my high power rig.
	Just short the antenna input to the RX to GND
	while in TX. Be careful with the 6790 as it doesn't
	have input protection like the 6830. The RF amplifier will
help. I would put a power meter on the RX line while you 	transmit to
make sure the RX power is a safe level.
	Open frame relays will work if mounted in a metal box.
	I use 2 P&B DTDT 25 amp relays for the TR in my
	4CX3000A amplifier up to 10 meters. 2 contacts in parallel
	at the output and single set for input with the last set
	to key the power. The coils are 115VAC but work very well
	at 28 VDC without buzz. I just bypass the amplifier
	in RX so you would have to configure one set of contacts
	to short the RX line.   fc 

-----Original Message-----
From: Jerry Kincade [mailto:w5kp at direcway.com]
Sent: Friday, February 21, 2003 8:06 AM
To: premium-rx at ml.skirrow.org
Subject: [Premium-Rx] Racal 6790 T-R switching


Gentlemen, I need some advice.  I want to use my 6790 paired up with a
T-368C (up to 400W key-down carrier on AM, a *lot* more PEP when modulated).
Of course, I don't want to fry the receiver's front end, so I'm looking for
a safe way to mute the 6790 during transmit. QSK is not needed, just good
old PTT switching. I understand the "A1" RF Amp module for this receiver has
built-in relay switching for muting. Naturally, my receiver does not have
one of these
1. Does anyone have an A1 module available for sale?
2. If not, has anybody invented a safe scheme for muting this receiver
during high power transmitter keying? I'm concerned that the standard old
coaxial T-R relay I'd normally use might not provide a safe level of
isolation for the receiver front end. There are acres of room inside the
6790, so a muting relay of some sort should be easy to mount, but I don't
want to reinvent the wheel here.
3. Or, am I worrying about nothing here, because the 50 db or so of
isolation from the coaxial relay is sufficient to protect the receiver? Keep
in mind that PEP under modulation could exceed 1500 watts on occasion. I
can't find any reference to how much power the front end can stand before
bad things happen.

How about it?

Thanks to all,
Jerry W5KP



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