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Re: Mast mounted preamps - I'm a believer!



I have some experience with reed relays in RF.  There are a few items of
concern that will help the situation.  First, make sure that the reeds are
of differing length.  When they are of the same length as in most cases,
they stick more frequently.  Secondly, if you can determine either from
the manufacturer or by observation with a microscope, obtain reeds that
have mossy Gold on one contact and bright Gold on the other but not of
the same plating. Lastly, do use a diode across the coil but slide a
ferrite bead on each side of the diode.  This should prevent RF from
rectifying and holding the contacts closed.  A small capacitor from each
side of the diode to ground also helps.  73   Cliff K7RR

On Mon, 18 Sep 2000, Chris Phelps wrote:

> Hi Jon, reed relays are notorious for sticking esp. if they are the cheaper
> ones like Radio Shack sells. I would use them in lots of projects where I
> needed low power consumption relays. I found that higher comercial grade
> ones that I pulled from old telephone switching controllers worked better.
> You might want to check and see if the strong rf from the X-mitter is
> saturating the coil and magnetizing the contacts ( you have a diode across
> the coil to protect the transistor from reverse flow out of coil otherwise
> it may be damaged and holding them on, it can also rectify the strong rf)
> causing them to remain closed. they are very close together and not much
> tension to pull them apart.
> Chris
> -----Original Message-----
> From: Jon Ogden <na9d@mindspring.com>
> To: amsat-bb@AMSAT.Org <amsat-bb@AMSAT.Org>
> Date: Monday, September 18, 2000 6:26 AM
> Subject: [amsat-bb] 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."
> >
> >----
> >Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> >To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> >
> 
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