[VHFcontesting] Median RF Noise Floor

[James Duffey]

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
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KK6MC
James Duffey
Cedar Crest NM