[Namaste-dev] 3.4 GHz Interference Study Update

Michelle w5nyv at yahoo.com
Fri May 9 09:05:14 PDT 2008


>From Kerry Banke:
Michelle - Just another incremental update on progress towards the 3.4 GHz interference study. Yesterday I set up the 30" dish/LNBF  in the back yard with a beacon  100' away. I was able to optimize the feed position and take preliminary Earth, cold sky and Sun noise measurements. I need to crunch the numbers but  off hand it looks to me like it's working just fine for our purposes.  It always amazes  me how well  we can see the thermal noise difference between pointing at the earth and cold sky with a good, low noise figure system.
 
Here are the preliminary numbers for the 30 inch offset dish with BSC421 LNBF:
 
Sun noise system test - 
Noise measurements:
Spectrum analyzer set for 2 MHz RBW 
Cold sky = -62.2 dBm
Earth = -59.3 dBm
Sun ( cloudy) = -58.7 dBm
 
Terrestrial weak signal test -
This will be performed using a signal source of know amplitude and frequency connected to a antenna of known gain
placed at a suitable distance from the equipment to be tested. This data should allow Antenna/feed optimization
and overall system gain determination, approximate noise floor calibration and frequency calibration.
Initial test results:
 
Test setup:
Beacon -20 dBm into dipole with reflector at 100 feet  assume 0 dB ant gain
Estimated path loss 73 dB
Spectrum analyzer set for 2 MHz RBW
 
Measured data:
Ant BW total between 3 dB points = 6 deg
Rx signal =  -5 dBm at spectrum analyzer including 1 dB cable loss
 Combined gain of antenna and LNBF  from measurements = 89dB  (-4 dBm Rx-(-20dBm Tx - 73 dB Pathloss)
Expected gain is total of Antenna Est gain of 26 dB and LNB gain of  65 dB printed on LNBF unit = 91 dB
The measured and expected gains show a reasonable agreement as a sanity check.




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