Hi Mark, N8MH
I have seen the pictures of your Landwehr 70 cm preamplifier and I know very well the model of coax relays used in it.
They are 50 ohm coax relays Tohtsu CX 120 P for printed circuits and can handle 150 watt pep at 500 MHz with an insertion loss of 0.2 dB and a crosstallk (insulation) of 35 dB with a VSWR of 1,08 at 1 GHz
don't worry about to clean the contacts because they are very large silver contacts and you just need to remove the side cover with your fingers and spry a contact cleaner over it.
I use four of them in my switching four polarizations switcher on a 70 cm crossed yagi as you can read into the AMSAT Journal March/April and May/June 2007
Have fun
73" de
i8CVS Domenico
----- Original Message ----- From: "Mark L. Hammond" marklhammond@gmail.com To: "i8cvs" domenico.i8cvs@tin.it; "Amsat - BBs" amsat-bb@amsat.org Cc: "Vince Fiscus, KB7ADL" vlfiscus@mcn.net; "K5OE" k5oe@aol.com Sent: Thursday, June 02, 2011 3:33 AM Subject: Re: Fixed! Re: Landwehr 70cm preamp device question?
Hello Domenico I8CVS,
I did take pictures while I had the cover off :) You can see and download
them here:
https://sites.google.com/site/marklhammond/hamradio
Indeed, they are labeled "COAXIAL RELAYS" as you suspected.
You can also see the "little white button" on the relays that I mentioned
previously.
73!
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 applications.
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.
Tanks
73" de
i8CVS Domenico
----- Original Message ----- From: "Mark L. Hammond" marklhammond@gmail.com To: "Amsat - BBs" amsat-bb@amsat.org Cc: "i8cvs" domenico.i8cvs@tin.it; "Vince Fiscus, KB7ADL" vlfiscus@mcn.net; "K5OE" k5oe@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
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.
73,
Mark N8MH
----- Original Message ----- From: "Mark L. Hammond" marklhammond@gmail.com To: "Amsat - BBs" amsat-bb@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]