[amsat-bb] Gardiner LO2398 Downconverter

[K5OE@xxxxxxx]

Well, the Houston flood seems to have seriously impacted our USPS mail 
delivery (no QSL cards since last Friday and where's my AMSAT Journal???), 
but today UPS brought me my latest toy, a Gardiner LO2398 MMDS downconverter. 
 See:  

http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=1241258231&r=0&t=0&show

Tutorial=0&ed=991351427&indexURL=0&rd=1

for a complete description.  There appear to be many more of these surplus 
units available.  Please note, the deal was for two d/c and power 
supplies/tee's that were "removed from service."  Both the power supplies 
were dead and only one of the two d/c works correctly (the other has a jumpy 
picture).  I've requested a replacement.  Still, a lot of "stuff" for $8.50.

Here's what I have determined so far:  
- Outwardly, these units appear similar to the AiDC 3733, but are nothing 
alike inside.  These things include a Motorola integrated FM receiver 
(MC13135DW) and a Zilog 1405 MPU (running 8 MHz).  Who knows what they do?  
Wireless LAN?
- The unit performs well with the integral antenna and gets a picture about 
on par with a 4 turn helix.  The antenna is a simple dipole with one 
parasitic element about 1-3/4" in front of the dipole.  Somehow, I expected 
it to be more sophisticated.  It performs better off the side than in the 
axial mode!  This could be a good lash up to an offset dish.
- The LO is in fact at 2398 MHz and uses an 11.9892 MHz crystal (x 200) for 
the IF.  Since it's IF is so much lower than the other units I've seen 
(Drake, CalAmp, AiDC), it leads me to believe it might perform very well at 
144 MHz.  For example, MMDS channel D at 2521 MHz comes in on cable channel 
14, or 127 MHz.  That is a much better conversion factor than the others.  
The crystal can be replaced without removing the board.  I calculate a 
replacement of 11.28 MHz will give the standard 144 = 2400 conversion.  There 
is a trim pot adjacent to the crystal.
- The RF amp appears to be tunable, with an itty-bitty vari-cap on the board 
near the "M" amp.  That could be interesting.
- You can see pix of the insides at:
http://groups.yahoo.com/group/AmsatTech/files/Gardiner_LO2398.jpg

I plan to order a crystal tomorrow and see what it does.  If anyone has any 
experience with these units, please comment.
73,
Jerry, K5OE
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