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

Mark L. Hammond marklhammond at gmail.com
Wed Jun 1 18:33:24 PDT 2011

Hello Domenico I8CVS,

I did take pictures while I had the cover off :)  You can see and download them here:


Indeed, they are labeled "COAXIAL RELAYS" as you suspected. 

You can also see the "little white button" on the relays that I mentioned previously.


Mark N8MH 

At 02:42 AM 6/2/2011 +0200, i8cvs wrote:
>Hi Mark, N8MH and All guys on the list.
>I am very happy that you solved the problem on your preamplifier and since
>you took the cover off I would like to know if the relays are or not
>"COAXIAL RELAYS" or just non constant impedance relays for AC or DC
>Can you take a picture on the inside of preamplifier and send it to me by
>email ?
>I remember that the owner of Landwehr was a 432 MHz EME'r in the early 1973
>and I worked him off the moon but actually I don't remember his call letter
>from Sweden.
>I believe that he dismitted the production of the above preamplifiers many
>years ago.
>73" de
>i8CVS Domenico
>----- Original Message -----
>From: "Mark L. Hammond" <marklhammond at gmail.com>
>To: "Amsat - BBs" <amsat-bb at amsat.org>
>Cc: "i8cvs" <domenico.i8cvs at tin.it>; "Vince Fiscus, KB7ADL"
><vlfiscus at mcn.net>; "K5OE" <k5oe at aol.com>
>Sent: Thursday, June 02, 2011 1:44 AM
>Subject: Fixed! Re: Landwehr 70cm preamp device question?
>> 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
>> 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.
>> 73,
>> 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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