[amsat-bb] Re: mmds downconverters for ao-51?

Wed May 5 05:38:51 PDT 2010

I have one of these all-in-one units on my shelf here.  The filter construction is *not* identical to the Cal-amp models, but you can use the same roadmap as in my article to figure out what is what.  It will be a little trickier to get to work reasonably at 2401.  This is because the input filter is a metal-ceramic (probably helical?) no-tune component that is soldered and glued to the board.  The frequency range 2300-2700 MHz really depends on what it was designed for--some of the I understand some of the Austrailian models work at 2401 right out of the box, but the one I have (designed for MMDS service in the US) is probably 20-30dB down from its peak around 2500 MHz.  The front end filter appears to be the bottleneck.  Like other MMDS converters in the US, this one has a 2278MHz LO that gives you a 123 MHz IF for 2401.

Replacing that filter looks to be a bear, though it might be possible.  If anyone has figured out how to do this without destroying the thin PC board, there would be many people interested.  I imagine it would work acceptably for AO-51 if you just bypassed the font-end filter, but if you have any PCS stuff in the 2.1 GHz range you might have issues from the image frequency.  I did that for my first S-band contacts with a Pacific Monolithics MMDS converter, using a horn antenna fashioned out of a large soup can it it worked fine from downtown Rochester, NY.

Andy K0SM/2

----- Original Message -----
From: "Michael Heim, KD0AR" <kd0ar at sbcglobal.net>
To: amsat-bb at amsat.org
Sent: Wednesday, May 5, 2010 7:36:51 AM
Subject: [amsat-bb] Re: mmds downconverters for ao-51?

You will be astounded with the signal you will get from one of these downconverters.  I used this modification:
http://www.rvhfg.org/articles/k0sm/basic%20mods.php

________________________________
Michael Heim
Chief Engineer, Forever Broadcasting
New Castle PA
WKST  WJST  WWGY
814-671-0666
Contract Engineer  
Cell: 330-502-6379
ARS KD0AR

________________________________

________________________________
From: "Gary "Joe" Mayfield" <gary_mayfield at hotmail.com>
To: amsat-bb at amsat.org
Sent: Wed, May 5, 2010 7:24:15 AM
Subject: [amsat-bb] Re: mmds downconverters for ao-51?

Wow, the famous 'cigar' antenna.  At that price you can afford to play with
it.

73,
Joe kk0sd

-----Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of jfloyd at es.vccs.edu
Sent: Tuesday, May 04, 2010 4:38 PM
To: amsat-bb at amsat.org
Subject: [amsat-bb] mmds downconverters for ao-51?

Has anyone tried one of the itfs mmds downconverters like this
one on ebay:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=110523087399&ssPageName=S
TRK:MEWNX:IT

for ao-51 s band downlink? 75 ohm out and looks cheesey but
less than $30 shipped. it's cheap enough for me to play so I
bought one to experiment with, maybe just to remove the
downconverter. I would welcome stories of your experience or
just advice.
Thanks
John, kn4ge
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