[hpsdr] WDSP: smeter calibration

[Scott Traurig]

I'm very sorry, Simon, but it does not seem that you understand. The dBm
levels in the S-meter are not incorrect. Why would you think that? Please
go back and re-read the topic on the forum.

The levels shown in the S-meter represent the total power in the selected
RX passband, either in S-units, dBm, or both, depending on the style
S-meter selected. This is in accordance with the ITU standards for S-meter
measurements.

The levels shown in the panadapter represent the total power in the
selected panadapter FFT bin width in dBm. There is no corresponding ITU
standard.

Since noise power is broadband and relatively monotonic, at least over 10's
to 100's of KHz, it scales perfectly with respect to noise measurement
bandwidth. CW signals, which generally fit within both the selected
passband and the FFT bin width, will measure the same in either case
because of of their narrowband characteristic. SSB phone signals can be a
bit confusing, but you simply have to remember that ANY RF POWER
MEASUREMENT MUST BE REFERENCED TO THE BANDWIDTH IT IS MEASURED IN. If you
measure the power of an SSB signal in a 2 or 3 Hz bandwidth you are only
measuring the power IN THAT 2 OR 3 HZ BANDWIDTH. If you measure the power
of an SSB signal in a 2 or 3 KHz bandwidth then you are measuring all of
the power IN THAT 2 OR 3KHZ BANDWIDTH. These measurements are NOT the same,
are NOT intended to be the same, and provide different views of the same
information, each with its own usefulness. The first measurement
(panadapter) allows one to understand how the total power is distributed
within the 2 or 3 KHz total bandwidth of the SSB signal. The second
measurement merely measures the total power for the entire signal (S-meter
measurement).

73,

Scott/w--u-2-o


On Wed, Jul 11, 2018 at 6:51 PM, Simon Eatough <simon.eatough at gmail.com>
wrote:

> Thanks, Byron, Scott. Yes I understand now. Might explain why cudasdr does
> some math maybe in a attempt to correct  the smeter levels. Would it be
> better to simply not display the dbm levels in the smeter at all then,
> since they are incorrect ?
> 73's
> Simon ZL2BRG
>
> On Thu, Jul 12, 2018 at 1:25 AM Scott Traurig <scott.traurig at gmail.com>
> wrote:
>
>> No calibration is required. Nothing is wrong. There are no "issues",
>> other than one must understand that all RF power measurements must be
>> referenced to a measurement bandwidth..
>>
>> See here:
>>
>> https://apache-labs.com/community/viewtopic.php?f=6&t=2463
>>
>>
>> On Wed, Jul 11, 2018 at 5:39 AM, Simon Eatough <simon.eatough at gmail.com>
>> wrote:
>>
>>> ***** High Performance Software Defined Radio Discussion List *****
>>>
>>> Hi Folks. I've been playing with a anan10  sdr app which the wdsp
>>> library to do the dsp processing. I've noticed that the peak signal levels
>>> in the pan adaptor / receiver passband are about 10-15 db lower than that
>>> reported by the WDSP library's GetRXAMeter() function.
>>> linhpsdr which also uses the wdsp library has the same issue.
>>> Wonder if anybody else has noticed this.
>>>
>>
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