[amsat-bb] Re: System Temperature Measurement

["Kenneth Shutt" <kgshutt@xxxxxxxx>]

James,

Here are my latest sun noise measurements.  The receive antenna is your 60cm
dish with your patch feed.  A DEM 13ULNA preamp is installed ahead of the
TSI AIDC 3733 downconverter with a 144 Mhz if into a FT-736R.  Data was
taken at 17:34 UTC ( 11:34 local ) on 29 December 2001.  Audio output of the
receiver was measured with a Simson 269 vom ( 5,000 ohms/volt ) on the 0-3
vac scale.  RF gain was set to obtain nominal 0.5 vac cold sky measurement.
AF gain was wide open.  A total of 5 measurements were taken and averaged
for the noise calculations.  There was very little variation in the
measurements ( < 5 % ).

FT-736 Audio Output:

Cold Sky ( El = 90 degrees )        0.54 vac
Sun Noise ( El = 36 degrees )      0.84 vac

Solar Flux @ 2.7 Ghz, 1600 UTC, 12/29/01, Sag Hill

SFU = 236 e-22 w/m^2/Hz

Y ( Power Ratio ) = (Voltage Ratio )^2 = (0.84/0.54 )^2 = 2.42

G/T = (Y-1)/I = (Y-1)(235/SFU) = (2.42-1)(235/236) = 1.41

For 21 dbi gain of 60 cm dish, G = 126

Tsystem = 126/1.41 = 89.4 K

Does this seem reasonable?

The receive system is performing very well.  I am looking forward to more
favorable AO-40 attitude in a few months to better evaluate system
performance.  Thanks for your advice and assistance.

73 de Ken - K5GUU
AMSAT-NA LM 1565

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