What Greg is describing is an RF sensed high-power attenuator. Downeast makes two products that can work to do this:
One is the AOS-144 ( $80.00) which switches RF thru a 50w attenuator to a factory adjusted level from 10 up to 100mw output for driving a transverter. The receive side is passed thru to a common SO-239 connector which is connected to the radio. To use it solely for a preamp a 50-ohm resistor can be tied across the BNC transmit output connector. This would be used in conjunction with TR relay for unswitched preamps like the P144VDG.
They also make the SSBT ( $65.00) safety switch bias-tee which might be more appropriate. It provides dc voltage to power the preamp over the coax line and senses RF for protection up to 50w. Again one would need TR relays for bypassing the preamp if you want to also use the antenna for transmitting.
But if you just want protection for a dedicated receive preamp either would work without need for a relay.
I know that 100w was mentioned, but these probably would withstand a momentary application of 100w such as the turn-on "burp" that some radios have. http://www.downeastmicrowave.com/cat-frame.htm
73, Ed - KL7UW
At 08:56 PM 2/16/2011, Greg D. wrote:
As others, SSB Electronics model that is RF switched. I *have* transmitted 100+ watts into it, though not on purpose, and it works just fine. I got the RF switched model as a "just in case" bit of insurance, and am glad I did.
It's been reported here a few years ago that sometimes there's a little "burp" of RF that squirts out when a transceiver is powered up. Seems unlikely , but if so, maybe that did it?
If I recall, the discussion was about people frying their AO-40 S-band down converters by accidentally transmitting into them. An somewhat less certain recollection is that someone came up with a simple circuit that would clamp the RF to a more forgiving, if not totally safe level. As an alternative to an RF switched preamp model, perhaps a stroll through the archives might net a different solution.
Good luck,
Greg KO6TH
From: k7trkradio@charter.net To: amsat-bb@amsat.org Date: Wed, 16 Feb 2011 13:59:41 -0800 Subject: [amsat-bb] pre amp help..
I just sent my ARR pre amp back to ARR for repair for the 3rd time !
(pretty sure I did not tx through it )
What are people using for pre amps. I only see the Mirage as an
alternative.
Any other choices. I'm kind of disappointed in ARR products. Is there a pre amp that you can tx through preventing accidental frying?
Any thoughts appreciated
73, Ted, K7TRK _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 144-1.4kw*, 432-100w, 1296-testing*, 3400-winter? DUBUS Magazine USA Rep dubususa@hotmail.com ====================================== *temp not in service