Tuesday, January 1, 2013

Local RF Noise

For anyone that's interested, here is a plot of the local RF noise on the 2m band at my location.  The antennas were pointed towards the east (90 degrees azimuth), and were raised 10 degrees every 30 seconds.  MAP65 software was used to visually record the ambient RF noise (red = strongest, blue = weakest).

The "cold sky" has a detected RF noise of around +23dB with my current settings, and with the antennas pointed at the horizon the noise is about +31dB.  This certainly makes detection of low-angle weak signals difficult!  Practically, the noise limits detection of most EME signals until the moon is above 20-30 degrees or so.

One thing I will sometimes do with EME is to raise the antennas +10 to +15 degrees above the moon's actual position.  With the vertical beamwidth of the array, this means a slight loss (1dB? 2dB?) in received signal strength, but can lead to a much bigger reduction in ambient RF noise detected.

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