[amsat-bb] Weak Signal Banquet NF numbers..

["Frederick M. Spinner" <fspinner@xxxxxxxxxxx>]

Here are the numbers that were measured at the Weak Signal Banquet at 
Dayton:

New DEMI 2.4 GHz Preamp (assembled by W1BFN):
   0.58 dBNF/16.95 dB gain
Old DEMI 2.4 GHz Preamp (assembled by W0FMS, measured at Winnipeg CSVHF 
meeting 2000):
   0.68 dbNF/11.78 dB gain

Modified Drake 2880, lengthing bandpass filter strips and IF cap mods (W0FMS 
modifications):
   6.00 dBNF/23.0 dB gain  @ 123 MHz IF, 2401 MHz center freq at RF

Same Modified Drake 2880, with the OLD DEMI Preamp above in front:
   1.25 dBNF/37.5 dB gain  @ 123 MHz IF, 2401 MHz center freq at RF

Transystem 3033 bought at the flea, unmodified.  Note the image freq  
concerns, though..
   1.42 dBNF/28.8 dB gain  @ 123 MHz IF, 2401 MHz center freq at RF

The NF debate about the Transystem applies-- but maybe someone can explain 
to me that when you pulse a broadband noise source such as the noise head on 
a new Agilent NF Analyzer, how the meter can distinguish one noise sideband 
from another if both are getting converted to the IF?  So I understand the 
problem, but why doesn't it affect the NF readings?

Anyway-- the T/S converter can operate in that range with careful mods, 
maybe an ISM filter, etc.... cheaply...

Interestingly enough, when I massaged these numbers through the
AO-40 spreadsheet, the gentlemen on the board harping the SSB converters 
have a point.  The SSB converters with a 0.8 dB system noise figure have 
about a 3 dB lower minimum discernable signal (noise floor) than the Drake 
w/preamp and/or the Transsystem.  Now if the massive gain could somehow be 
handled, the Transystem with either DEMI preamps in front of it could have 
an edge on the SSB converter.  Also a Drake that had the 2 dBNF or so mods 
done to it that had a DEMI preamp in front of it could also outperform the 
SSB converter.

But if not, for the $350 I've saved not getting overpriced SSB electronic 
equipment, I'm close enough with the Drake/DEMI preamp or the Transystems 
units with the 3'X2' BBQ's (hell, I spent it on a G-5500 Yaesu rotor that 
seems to be backordered from Japan at Dayton..)

So, this in hand, maybe I'll come up with some suggestions in the next few 
weeks for cheap, simple Mode-S recvs and I also have some ideas for mods to 
the Transystems.

Fred W0FMS


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