[hpsdr] PowerSDR + S-Meter + CAT S-Meter issues

[Warren C. Pratt]

Hi Dick,

I can provide some insight into the second item you mention.  By far the
easiest way to compare meter readings with what's shown on the spectrum
display is with a coherent signal such as a carrier.  You've already
observed that the strength is what you expected when using such a signal.

The S-meter responds to the vector sum of all the energy within the selected
filter passband.  Therefore, with only "noise" in the passband, the S-meter
reading will vary depending upon the filter bandwidth you've chosen.
However, with a real signal of reasonable magnitude, the signal becomes the
dominant effect and you get a correct reading of its strength (assuming
you've calibrated).

The panadapter works slightly differently in that it displays a set of
"bins" that extend across the screen.  A coherent signal will dominate in
one or more bins and it's amplitude is correctly displayed.  However, the
amplitude of the noise floor will vary depending upon several settings (FFT
size, window selection, averaging mode) used in generating the panadapter
display.  The smaller the bin-width (larger the FFT size), the less noise
energy that will be in any bin and therefore the lower the noise floor on
the display.  Using these larger FFT sizes is useful to be able to see weak
signals, for example in the digital modes, that otherwise could not be seen
and perhaps also not heard.

In case you haven't seen it, there's a bit more explanation of some of our
signal processing features in this document:

<http://openhpsdr.org/wiki/images/b/b4/POWERSDR_USER_NOTES.pdf> 

73,
Warren  NR0V

-----Original Message-----
From: hpsdr-bounces at lists.openhpsdr.org
[mailto:hpsdr-bounces at lists.openhpsdr.org] On Behalf Of Dick Lichtel
Sent: Wednesday, May 15, 2013 3:37 PM
To: hpsdr at lists.openhpsdr.org
Subject: [hpsdr] PowerSDR + S-Meter + CAT S-Meter issues

***** High Performance Software Defined Radio Discussion List *****

With CAT control set to PowerSDR, PSDR seems to be sending erroneous values
to HRD & Bobmeter. S-meter values  on HRD & Bmeter are S-9+10 for 
a signal around   S7. The signal level ( in dBm) reported by HRD does 
match that shown by PSDR.

If the CAT control is set to TS-2000, HRD reports a signal strength 1 or
2 db lower than that shown by PSDR.

The other problem is with the value of the signal strength (and S-meter)
shown by PSDR. With no antenna connected, the S-meter shows S1 and strength
is -120dBm. The spectrum display shows the noise floor below -140dBm. If I
hook up a antenna on 10M, the display shows my noise floor ~ -125dBm but
PSDR shows an S3 and -106dBm. Tuning in on an actual signal(like a carrier),
the signal strength reported seems to match that shown in the spectrum.


Dick KD4JP


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