|To:||Jim Brown <email@example.com>,"Tower Talk List" <firstname.lastname@example.org>|
|Subject:||Re: [TowerTalk] ARR Preamp Failures|
|From:||W0UN -- John Brosnahan <email@example.com>|
|Date:||Mon, 04 Oct 2004 11:25:19 -0500|
Not exactly a TOWER question--but I will make a couple of comments.|
1) Does your 6M GaAsFET preamp have back-to-back diodes on the input for protection? I have found that to be helpful when running 50 KW pulses at 49.92 MHz using the ARR preamps.
2) The failure you experienced during your recent QSO seems to be when there was 1) no lightning and 2) no other radios transmitting. Is that correct?
3) If so then I would be suspicious of my own 6M TX signal getting into the preamp. And you say you are detecting the RF for T/R switching. I HATE that approach--too many things can go wrong. You need to be back into RECEIVE mode well before you send out any TX signal.
My best guess is that you are shooting yourself in the foot with your own TX signal.
BTW I always put shorted 1/4 wave stubs at the antenna feedline. This provides
some static drain from the antenna, it also does some even harmonic attenuation,
and it provides significant reduction of the HF signal levels. I consider it good
design practice. And in the case of VHF radars it also speeds up the PIN diode
T/R switching time from about 6 uS to 3 uS.
I have used literally a HUNDRED ARR preamps over the years--almost all being the GaAs FET models with very good luck. But if the isolation of the TR switch is low you CAN blow the preamps with your own tansmit signal-- if you don't run back-to-back diodes on the input connector to the preamp.
At 09:41 AM 10/4/2004, Jim Brown wrote:
Last winter, I bought an ARR mast-mount GaSFet preamp for 6m. It has now failed for the
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
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