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Mast mounted preamps - I'm a believer!



Hey guys,

Well, this weekend, I finally took a break from most of my household chores
and finished construction and installation of my mast mounted preamps (Gotta
get ready NOW for P3D!).  It's a homebrew project I started last spring.
The amps are an ARR GaAs Fet on 2m and a Down East Microwave GaAs FET amp on
432 MHz.  The voltage regulation and relay circuits to switch the amps in
and out on TX/RX are my own design.

I knew the amps added a lot of signal gain as I'd tested them out in the
shack.  But they also added a lot of increased noise after about 60 to 70
feet of 9913.

So yesterday afternoon, after kluging a way to secure the amps and heatsink
into the waterproof housing (secured with bubble wrap stuffed between the
housing walls and the heatsink (The amps, relays, voltage regulators, etc.
are mounted on the heatsink)), I mounted the box about 7 feet up my mast (as
far as I could reach and still easily disconnect things).  It's not ideal as
I still have probably 20 feet or more of coax between the antennas and
preamps.  I have a Yaesu G5000A (I think that's the number) El rotor I
picked up at Dayton that I plan on putting up next spring (no time now -
getting married in less than 4 weeks!).  I'll also replace my fiberglass
tube with a solid rod at that time.  It's a Radio Shack telescoping mast so
getting the antennas down won't be that hard.  Well, OK, yes it will!

OK, the point of all this is WOW!  Do these things work!  I was able to copy
UO-14 on a very, very low elevation pass and work several stations.  The
pass really got no higher than about 10 degrees.  It was pretty cool to hear
just a couple of stations on the bird at the start and end of the passes.
Signals were easily 59 plus with the preamps.  They were about 51 to 52
without.

Then I talked to myself on FO-29 for a while.  It was also a very low pass
and signals were good again.  I probably wouldn't not have been able to copy
near as much without the amps on.  On the next pass, I managed to work about
4 or 5 stations, a couple when the bird was getting very close to the
horizon.

So I am a believer!  Mast mounted preamps work great.  I would say they are
a necessity!

I've got one minor snag with these guys though.  When I have the preamps
turned OFF and key the rig my power amplifiers on, the PTT line sticks and
the amps stayed in TX mode.  The preamps and amplifiers are both controlled
by the PTT line.  Things work fine with the preamps on, but again, the
amplifiers stick with the preamps off.  I wasn't able to measure voltages
since my VOM is at my fiancée's place for something.  I'll get that an
troubleshoot tonight.  But does anyone have any ideas?  The PTT lines going
to the preamps pull down a ground line on reed relays that switch voltage on
and off to the preamps and RF relays.

I took pictures of the box and once developed, I'll send them to K5OE or
whoever has the homebrew website.

73,

Jon
NA9D

-------------------------------------
Jon Ogden
NA9D (ex: KE9NA)

Member:  ARRL, AMSAT, DXCC, NRA

http://www.qsl.net/ke9na

"A life lived in fear is a life half lived."

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