Topband: noise floor

[Guy Olinger K2AV]

Several things here...since you are looking for comparison numbers.

IF one has a calibrated S-meter (can now actually be done with a K3 with
latest firmware and utility), S9 is 50 uv into 50 ohms, which is -73 dBm, an
easy number to remember. I have verified my K3 with a precision step
attenuator.

Noise must be specified along with the bandwidth used for measurement, or
converted to a per Hz reference for comparisons with varying bandwidths.

Noise power here using SSB bandwidth, 2.7 kHz, is just kicking S5 on my
calibrated K3 (50uv S9, 6db per S unit bar, 5 db per over S9 bar). That
would be 4 times 6db or 24 db lower than -73, or -97 dBm.  Most of that
noise is my mysterious buzz from somewhere which the K3 NB will drop to
somewhere in the S3-S4 range (mostly solid S3 light).

If I narrow my bandwidth to my customary CW 350 Hz, the S meter is just
kicking S4, and with NB just kicking S2. S4 is -103 dBm and S2 is -115 dbm.


Last night's QRN peaks on 160 (using 350 Hz) were at and well over S9 the
whole time I was listening to the Stew Perry warmup, dropping back at best
to S6 or S7. On this night the band was 10-15-20 db noisier than my
neighborhood.  On quiet nights, the NB allows me to hear stuff I can't work.


I seriously doubt that either W4ZV or W8JI would consider my location
"quiet".  In your case -80 dBm steady state noise in daytime (S8) is pretty
gruesome if you're talking CW bandwidths.

I live just southwest of Raleigh, NC.

73, Guy.

On Sun, Oct 18, 2009 at 10:30 AM, Pete Parisetti <hb9dsu at gmail.com> wrote:

> Hello everybody from a newcomer to the list.
>
> I have a question. I would like to understand if my suburban location is
> significantly more noisy than others or not. To do so, it is handy to have
> the noise floor measured in dBm - something I can do with my SDR 5000a. The
> value is around -82 dBm in conditions which I would call "bad" and around
> -90 when "good", measured with the TX antenna (inverted L, 17m vertical/23
> horizontal).
>
> Would anybody else with the same rig (or similar) share their numbers?
>
> Thank you very much in advance and 73.
>
> Pete
>
> ___________________________
> Pete Parisetti MM0TWX - HB9DSU
> for music, ham radio and more
> visit http://www.hb9dsu.com
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