Jim,
I think you mean, V/m, not mW/m. BTW, you also need to specify bandwidth.
This ITU report expresses everything in terms of the external noise
figure, Fa of a short grounded monopole over a perfectly conducting ground.
https://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.372-15-202109-I!!PDF-E.pdf
This should be a good approximation of the external noise figure, Fa of
an efficient vertically polarized antenna (like the one that we normally
use for transmit). You can add this number to -174 dBm to get the noise
power normalized to 1 Hz at the antenna terminals. For a given receiver
bandwidth, BW in Hz, you can add 10*log10(BW) to get the power in that
bandwidth in dBm. For example, per figure 2 of the report the external
noise factor at 2 MHz due to man-made noise for a "quiet receiving site"
is around 45dB. That translates into a noise floor of -129 dBm/Hz. In a
200 Hz receiver bandwidth, that would be a man-made noise level of -106
dBm at the terminals of our efficient vertical antenna. Per figure 39 of
the report, the noise level in the "City" would be around 23dB higher
(i.e. -83 dBm in a 200 Hz bandwidth).
73, Mike W4EF.....................
On 6/14/2026 12:22 PM, Jim Brown via Topband wrote:
On 6/13/2026 5:57 AM, Carl Luetzelschwab via Topband wrote:
160m has an approximate 10 dB increase in man-made noise in a
residential noise environment and an approximate 5 dB increase in
man-made
noise in a rural noise environment.
80m has an approximate 8 dB increase in man-made noise in a
residential noise environment and an approximate 4 dB increase in
man-made
noise in a rural noise environment.
Thanks Carl. I've seen this cited before.
Several observations. The paper notes increases on the order of 14-20
dB in urban environments, and this was published in 2019, probably
from data in a subsequent year (it takes time to do this stuff and
publish it). Assuming 2018, this 8 years later, and it's gotten much
worse.
I'm sticking with 20 dB as a WAG.
BTW -- there are many definitions of power articulated in dB, each
with a reference. The most common for dBm I'm familiar with is dB with
respect to a 1 mW, and our most common citation in ham radio is tied
to the signal at the input of our receivers, displayed on an S-meter.
But the real quantity is field strength in mW/m, while the voltage at
the RX input is totally dependent on the antenna, its characteristics,
and the feedline. In other words, dBm at the RX input is meaningless.
73, Jim K9YC
_________________
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
