[OKDXA] Radios and noise

[John Geiger]

Also, you would need to know Preamp/Attenuator status of the 2 stations, as
turning on the preamp will show much more noise on some radios.  No radios
need to have the preamp on on 30 meters and below, they are already plenty
sensitive for the low bands.

On Fri, Jan 27, 2017 at 3:16 PM, Roger Simpson <rksimpson1 at cox.net> wrote:

> Gentlemen:
>
> Thanks for your replies regarding S Meter Readings on CW vs. SSB.  I never
> thought of this before but I guess you are saying that assuming the signal
> level for every 10Hz slot from 7,100,000 Hz  up to 7,101,000 Hz was exactly
> -60 Dbm then the way receivers are designed then if your total bandwidth is
> say 2.4Khz then you are going to hear more noise out of the speaker than
> you would if you have a 500Hz bandwidth -- given that the background noise
> on the band is the "same" in any given 10Hz slot.
>
> I guess I was a little slow to the draw but I did not realize that the S
> meter was reporting on the aggregate signal that is in the bandwidth -- not
> just the strongest signal.  I guess another way to say this is that the
> S-meter reading relates to how loud the noise is that is heard on the
> speaker -- assuming that the audio level "volume control" is not changed as
> you change modes / filters.
>
> I guess I've been living in a cave over here. I just did an experiment on
> CW where everything stays exactly the same except I switch from a 250Hz
> filter, to a 500Hz filter, and then a 1200Hz filter. Lo and behold the
> S-meter changes. So the S-meter doesn't really have a DIRECT correlation to
> the noise level going on in the band. So I can't just say I've got a high
> noise level [or a low noise level] on 40m right now because my S meter says
> some given reading.
>
> Implicit in this is that if W5XYZ says "the noise level on 40m CW right
> now is S9" and W5ABC says "over here at my QTH the noise level on 40CW is
> S6" it could be that they are both seeing the same thing. We don't know
> unless we know what the bandwidth is that they are using. Also, of course,
> who is to say that rig manufacturer X and rig manufacturer Y have
> comparable S meter readings even if the mode and bandwidth are the same.
> Also various stations have different antennas. An antenna with a 40meter 3
> element yagi at 100 feet might given a different "noise level S meter
> reading" than a 40m dipole at 40 feet.
>
> I guess it is the margin between the signal to noise in terms of DBs that
> is important -- not some particular noise level S meter reading.
>
> 73  Roger  K5RKS
>
>
>
>
>>>
>>
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