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WEFAX question



I'm looking for some help with WEFAX reception.

I'm getting the signal, but with too much SNR to decode anything 
properly (Multimode for the Mac can do a poor image if I use a narrow 
enough filter and put the receiver in FSK-FAX mode, but that chops 
out too much data).

I'm pointing at GOES-8 with a 44 element loop yagi (mounted on a 20+ 
foot tower section on the roof of a 4th floor building) and a 22 dB 
GaAsFET preamp mounted on the antenna.  I've got about 6.7 dB of 
feedline, surgesupressor and DC-injector loss (actual measured values 
at at 1691 MHz for all but one coax segment).

The preamp is a Down East Microwave 1691 MHz 1 dB NF preamp, which 
isn't bandlimited at all, but the total power out of the system is 
-18 dB on a .1 to 18 G broad-band power meter, so I don't think it's 
overloaded.  I've pulled the amp off the roof and with some help 
tested it and it seems to be almost linear ~27 dB amplification at 
200 MHz and 20 dB at 1691 MHz.  this is all feeding into and Icom 
R-9000 receiver which gets full quieting at a -100 dBm FM signal from 
a signal generator at 1691 MHz.

All the link budget I've calculated says I should have plenty (based 
on the power output levels published in the 1990 edition of the 
Weather Satellite Handbook, I can't find the power output published 
on any of the GOES or WEFAX web sites I've found so far).  I'm 
working on checking NF numbers for the R-9000 (they just print 
sensitivity in micro-Volts in the manual).  I should have a better 
than 8 dB SNR at the input to the receiver, but I don't really get 
anything above the noise in FM with the wide (30 kHz) IF filter. If I 
narrow the filter I can hear it better, but not well enough to 
receive images in FM mode.

Unfortunately the spectrum analyzer we have stops at 1.5G, so I can't 
see what the signal level is directly.

The one thing I can't find on the web is what the GOES-8 polarity is. 
Right now the antenna is vertically polarized.  tomorrow I'm going to 
bring in a couple of HTs and get some help to try and adjust that, 
but if that doesn't make any difference I'm stumped.

Any thoughts on the effect of polarity, or anything else I haven't 
considered would be greatly appreciated.

thanks!
-- 

-debbie
Debbie Fligor, n9dn       Communications Designer/Engineer, CCSO, Univ. of Il
email: fligor@uiuc.edu          <http://www.uiuc.edu/ph/www/fligor>
"Every keystroke can be monitored. And the computers never forget."
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