John - I haven’t seen a response to your question on the realism of the noise
floors shown in ITU-R P.372-10, so I thought that I would take a crack at it.
I think the numbers you came up with are representative of what one sees in
practice, with perhaps the 6M number being a bit high. I base this on my
experience roving where one sees big swings in noise from remote areas away
from civilization to the industrial sections of big cities which are quite
noisy, particularly on 6M and 2M. In all fairness, the value for noise in
Figure 10 differs from that in Figure 2 by several dB, with Figure 10 giving
-118dBm or so. That seems to me to be a more reasonable value, but recall that
there are swings of 5dB to 10 dB from these numbers. That the ITU numbers are
reasonable should be no surprise, they were generated from measured data at
various locations, including the US.
NTIA/ITS has an active program measuring surveying the spectrum at various US
sites, including Chicago, Denver and San Diego quite recently. You can browse
the NTIA/ITS technical reports/memos/papers here:
< http://www.its.bldrdoc.gov/publications/2553.aspx >
Here is the April 2014 report on the Chicago survey:
< http://www.its.bldrdoc.gov/publications/2756.aspx >
The Denver and San Diego measurements are right below that.
The measurements are for field strength, dBuV/m, so you will need to do several
conversions to get them in dBm.
This report:
< http://www.its.bldrdoc.gov/publications/2553.aspx >
is probably the most useful, it details measurements of noise in the Boulder
and Denver CO area at 112.5, 221.5, and 401 MHz. These are not in the ham
bands, but the 221.5 and 401 are close. More importantly, this report compares
this measured data with the predictions of ITU. It also includes noise
variations with time of day, which can be substantial.
There are spectrum surveys for Los Angeles and San Francisco made in the 1990s
in there somewhere too.
NTIA thinks that VHF begins at 100 MHz and HF ends at 30 MHz, so data at 50 MHz
is a bit hard to come by. Here is an old, but very interesting report that
includes noise data from the Broadcast band to 250 MHz noise data from a
variety of sources.
< http://www.its.bldrdoc.gov/publications/2736.aspx >
It includes measurements at 48 MHz, close enough o 6M to be useful. The values
shown are consistent with the ITU report, but not exact. Of interest, at least
to me, is the noise as a function of distance away from power lines, and
ignition noise measured at busy intersections.
I hope that this has helped. - Duffey KK6MC
--
KK6MC
James Duffey
Cedar Crest NM
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