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Pre-amp Switching Questions



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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