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Re: Downconverter for AO40 ?



>The 3 most common are the Surplus dc's available from K5GNA
>(http://members.aol.com/k5gna).  I have 2 of the AIDC-3731's.

Currently this is the best option, the newer units are ~=1.0 dBNF ~=37dB 
gain with a front end filter that will cut off most out-of band interference 
and images.  They are not surplus, K5GNA buys them from the factory now, I'm 
fairly certain.  If you are on a budget, the "2nd" grade ones (the one I 
recently bought is 1.1 dBNF, 37 dB gain, 122 MHz IF) are $68 shipped in the 
US.  The "1st" grade ones are guaranteed to be <1.0 dBNF and are converted 
to 144 MHz IF for you.. they are $108 delivered.  Check e-bay for seller 
K5GNA.

He will ship out of the USA, too

>
>Down East Microwave (http://www.downeastmicrowave.com) has several low
>noise figure dc's, these seem to be pretty popular as well.
>

My personal opinion is that the Transystems work better.  SSB and Kuhne and 
others make commercial downconverters that work great, all tend to be quite 
pricy compared to the Transystems route. 3x-5x as much.

>And the old Drake 2880 (I think, not sure on the exact model #) is still
>in use, they have a terrible noise figure though and require some form
>of low noise preamp in front of them to be effective.
>
Honestly, the most sensitive and stable combo is my Drake 2880 with a DEMI 
(old style) preamp.  Works like a charm.  Inconvient compared to the 
Transystem mentioned above.  I'm going to try a L/S combo patch on my 4.5' 
DH Satellite dish soon (intention was by field day, but I'll probably only 
have a S receive patch and U on a WA5VJB cheap yagi by then) and I already 
know this combo won't work due to desense problems, so I recently bought the 
Transystems above.

>Also note that you will need some form of parabolic dish for this type
>of endeavor.  The 3 ft bbq grill dish can be a good starter system, but
>does not have enoug gain to hear the transponder noise floor, so you
>won't be hearing everything possible.  I currently have one of these
>dishes and a 1m aluminum spun dish from DH Satellite
>(http://www.dhsatellite.com)
>

The prime focus dishes from 3'-10' range are the way to go with either a 
G3RUH patch ($$$) or a W0LMD (http://www.ultimatecharger.com/dish.html) 
patch if you want a primo system.  Surplus PrimeStar or other FTA TVRO type 
offset-fed Ku-dishes 90 cm or larger are another alternative, maybe cheaper 
than the DH Satellite dishes.  But they are best fed with a helix, from 2.5 
to 5.5 turns (depending on the exact characteristics of the dish) and the 
best efficiencies you can get from this system is 45%-55% due to the extra 
sidelobes of the helix.  The prime focus/patch combos can have up to 60%-70% 
efficiencies, and the circular G3RUH style patches have much better axial 
ratios then most casually built helixes and even tweaked one.

If you live in the Midwest, DH Satellite will let you buy dishes in person 
for cash.  Call them first.  Ones with dents and dinks in the paint that 
might (or might not) effect Ku can be had at a discount, but only if you go 
there in person (this is from my experience a few years ago).  They are 
located in Prarie du Chien, WI.. nice area and nice drive.  They are 
reasonably close from about Chicago on the East, Des Moines on the West, 
Minneapolis on the North and maybe Springfield, ILL on the south.

The Transystems need some sort of 15V or greater power injector, so the 
"external preamp" power on the 847 doesn't cut it.  There is a standard 
(high dropout) 7812 internal to the Transystems..

Fred W0FMS

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