[RFI] Ambient Noise Levels

W0UN -- John Brosnahan shr at swtexas.net
Thu Aug 10 09:19:27 EDT 2006

At 11:20 PM 8/9/2006, Jim P wrote:
>I HAVE heard brief, slow rises and falls of broad-band
>white noise several times in the last couple of years
>on 10 Meters; the first time I thought the rig had
>experienced some sort of 'issue'.  The next couple
>of times I was primed for it, and I checked a couple
>different RIOMETERS *1 located in the same
>It was 'the sun'.

I did planetary and solar radio astronomy in the 1970s.
This was done at HF and low VHF -- 7 to 80 MHz --
using a pair of large corner reflector antennas mounted
on circular railroad tracks and configured as an
interferometer to distinguish space signals from terrestrial
signals.  (Space signals drift in position due to the rotation
of the earth, while terrestrial signals do not.)

Solar flares can create large amounts of noise across
this entire spectrum.  Often starting in one relatively
narrow range of frequencies and drifting across the

But Jupiter can also make a lot of noise, peaking when
its moon, Io, is in particular locations.  This noise is
most easily detected on 15M but can be detected from
20M to almost 6M.  It sounds like surf breaking on the shore.
It requires a quiet band, a modest Yagi pointed at Jupiter,
and Io in the proper position.

Extra-terrestrial sources are also used as noise calibration
sources in this frequency range.  One of the best is Cassiopeia A.

While most noise is man made or from lightning, there are
some very interesting sources that can be detected in a
quiet location by a decent ham station..

The 7-80 MHz radio astronomy observatory at the University
of Colorado (where I worked in the 1970s) is no longer operational,
but if it were then BPL would be the death of it!


73  John  W0UN

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