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Pre-amp Switching Questions
- Subject: Pre-amp Switching Questions
- From: JOppen6115 <JOppen6115@xxxxxxx>
- Date: Sun, 1 Mar 1998 01:23:30 EST
Hi everyone,
I have a couple of questions about the best way to use my new home brew, 435
MHz pre-amp. It uses a MGF1402 GAs-FET transistor which I really don't want
to blow up too many times. I intend to switch it out of the line using a pair
of coaxial relays.
1) Is it adequate to use the "pre-amp" line on the FT-736 to control the
switching, or does this allow transmit RF to bake the transistor moments
before the relays switch over? Perhaps a sequencer is required to get the
timing right? Does the FT-736 incorporate sequencing into the pre-amp line?
(I checked the manual and there is no indication that it does.)
2) Is it possible to add RF switching to a homebrew pre-amp? If so, I would
prefer to use this as the ease of use and "idiot proofing" would likely make
it live longer. I have concerns about the RF getting to the pre-amp before
the relays switch. Commercial ones do it, but I have never seen plans
published for a pre-amp.
3) Does anyone have any thoughts on the use of a 50 ohm load to protect the
input of the pre-amp, as shown in the ARRL handbook? If it's not necessary,
I'd like to avoid it, since it will use one additional relay ahead of the pre-
amp, increasing both cost and loss.
4) What is the best method for tuning up a pre-amp? I am having trouble
finding a reliable, weak signal source, and am a little confused by the
descriptions of how to obtain the best gain and noise figure.
I really would appreciate hearing any ideas or experiences that might help
with this.
Thanks and 73,
John Oppen, KJ6HZ
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