Re: SDR operated with a noise source


jdow
 

Until you calibrate it there is no way SDRC can be thought of as being calibrated.

Without a thorough of what Simon is displaying you cannot take the spectrum levels as meaningful.

Without an even more detailed knowledge of the S-Meter function you cannot track it back to anything meaningful, pretty much the same as your average rice box. (I have managed to completely fool Simon's S-Meter tool by 20 dB or more. Unless he changed it the tool is merely a "keep the bloody ignorant hams whining about wanting an S-Meter shut up.)

SDRC is very pointedly not a measurement system giving precise readings of power. And it probably cannot be converted into such a thing without a gawdawful amount of work.

But, you are welcome to try.
{^_^}

On 20210114 07:40:58, Allan Isaacs wrote:
Hi Willi
I tried lots of settings, visual gain and receiver gain, bandwidth etc but
the meter consistently read 6dB or more too high compared with the trace..
I then set the receiver to 500KHz scan with AM bandwidth to 2Hz and the
meter read correctly. Switching to AM 20KHz and it read 10dB too high.
I guess the meter is only good for comparative readings on a proper signal
but on noise you need to look at the trace and read off the vertical
scales..
If there was a trimmer so that you could tweak the meter to read the same as
the trace it would be nice, but I'm only experimenting with a noise source
to take the place of a tracking generator..
Allan G3PIY

-----Original Message-----
From: main@SDR-Radio.groups.io [mailto:main@SDR-Radio.groups.io] On Behalf
Of Willi Passmann
Sent: 14 January 2021 13:38
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] SDR operated with a noise source

Allan,
As I understand it, values would be equal only if you could select the
same bandwidth for the spectrum range and the demodulation range. But
you can try and tell us what you find out :-)

vy 73,
Willi, DJ6JZ

Am 14.01.2021 um 13:47 schrieb Allan Isaacs:
That does seem to make sense Willi.
If I measure the noise source with a wideband power meter it tells me it
is
0dBm so the noise within the selected bandwidth of the SDR at 190KHz is
summed over the 3.5KHz setting of the selected AM mode.. Presumably, all
things being equal, if I selected CW 50Hz the meter reading would be
closer
to that shown in the display?
Allan G3PIY

-----Original Message-----
From: main@SDR-Radio.groups.io [mailto:main@SDR-Radio.groups.io] On Behalf
Of Willi Passmann
Sent: 14 January 2021 12:35
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] SDR operated with a noise source

Allan, the different readings probably are related to different
bandwidths. 190 kHz for the spectrum and waterfall display, but maybe 3
kHz (or whatever you selected) for the demodulated signal that the S
meter reflects.

vy 73,
Willi, DJ6JZ

Am 14.01.2021 um 13:25 schrieb Allan Isaacs:
The noise signal looks like -116dBm at 190KHz and the meter shows
-109.7dBm.

















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