P3 base line changes with span with.

[KD7PY]

I was using the P3 to capture a pix of the interference that I have on the 6 meter band calling frenquency to send to the FCC.

I captured a pix with the span set on the P3 at 100 kc,
then I reduced the span to 10 kc and captured a pix.

but I noticed that my noise floor with the span set at 100 is -125 dbm  this was adjusted with the XG3.
but when I reduced the span to 10 kc the noise floor changed to  -135 dbm.
as I reduce the span from 100 kc it hold steady untill reduced to 50 kc and as I narrow more the noise floor drops as it is being reduced....

what is going on?

Ed   K7WIA

[KD7PY]

I just did a check with the XG3 at -73 dbm it is right on at 100 kc span, and it is also right on with in 1 or 2 dbm at 10 kc..   but it is just the base line that drops.... ?

Ed K7WIA

[Stephen G4SJP]

Ed,

If you read through page 17 of the manual, it explains why the noise floor
(base line) changes.  This is the same effect you notice when reducing the
IF bandwidth on the K3 - a narrow setting will produce a lower s meter
reading than a wider one.

The pertinent paragraph is:

"The noise level will generally be lower on the P3
display compared to the K3 S meter. The reason is
that the effective bandwidth of the P3 is generally
one display pixel, which is approximately span /
450. The smaller the bandwidth, the less noise. For
example, if the span is 45 kHz, the effective P3
bandwidth is 45,000 / 450 = 100 Hz. If the K3
bandwidth is 400 Hz, it will show a 6 dB (one S unit)
higher noise level than the P3."

There's nothing wrong with the P3, it's just the laws of physics!

73 Stephen G4SJP

On 7 November 2011 17:09, K7WIA <[hidden email]> wrote:

> I just did a check with the XG3 at -73 dbm it is right on at 100 kc span,
> and
> it is also right on with in 1 or 2 dbm at 10 kc..   but it is just the base
> line that drops.... ?
>
> Ed K7WIA
>
> --
> View this message in context:
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[KD7PY]

I found my answer,,,  RTMD.....  page 18 of the manual

Ed