[amsat-bb] Fixed! Re: Landwehr 70cm preamp device question?

Mark L. Hammond marklhammond at gmail.com
Wed Jun 1 16:44:46 PDT 2011

Hello All,

You gotta love a happy ending ;)

Thanks to I8CVS, Domenico; Vince, KB7ADL; and Jerry, K5OE for the advice and coaching with troubleshooting my Landwehr 70 cm preamp.

I took the cover off and applied 12V, and the two relays closed----or did they?!?  

One side looked good, while the other side didn't quite push the "little white button" enough to make the contacts meet.  It was stuck--just a gentle push with the finger, and I could tell it had become "unstuck."  Inserted back in line, and bingo!  It's working just fine.  

I have resisted my urges to spray something down in there...figure I can unstick it the same way another time, should it happen.  Looks like the preamp was made in 1990, based on the dates of the relays. 

What I was seeing seemed like it might be a relay issue on one side (could hear a rise in noise, so the relay at the output side (rig) was working--but the relay on the input side (antenna) wasn't.  So, when powered, the input relay didn't switch over correctly--what I was seeing now makes sense!

Anyhow, it wasn't the GaAsFET after all.  

Thanks again for the help, guys.


Mark N8MH 

>>----- Original Message ----- 
>>From: "Mark L. Hammond" <marklhammond at gmail.com>
>>To: "Amsat - BBs" <amsat-bb at amsat.org>
>>Sent: Tuesday, May 31, 2011 8:00 PM
>>Subject: [amsat-bb] Landwehr 70cm preamp device question?
>>> Hello All,
>>> I have an old Landwehr preamp that apparently uses the MGF1402 device
>>> (does that sound right?).  It's not working so I presume it's the
>>> GaAsFET.
>>> Can the MGF1302 be substituted for the original MGF1402?  Or can
>>> anybody recommend another device for the 70 cm Landwehr?
>>> I need to do something...
>>> Thanks in advance!
>>> -- 
>>> Mark L. Hammond [N8MH]

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