Even worse, your weak echo power is competingwith the galactic noise power coming from the sky surroundingthe Moon that falls within your antenna pattern, plus the groundnoise picked up by minor lobes of your antenna, plus receiver noisepower.
Example. Continuing the previousexample, suppose
the sky near the moon is at the (quiet) temperature
of 15K and your minor lobes are seeing the ground
(at 290K) for a total antennatemperature
of (say) 80K.Your receiving system temperature is (say) 120K.
This equates to blackbody noise of
kTB = 1.38 x E(-23) x (80 + 120) x 50
= 1.38x E(-19) W = -188 dBW
within a B = 50 Hz passband, giving an echo-
to-noise of
- 177.5 - (- 188) = 11.1 dB,
a very respectable echo.
next page
previous page