HDSDR

[W0IVJ]

I am using HDSR 2.70 with SDRplay. When I input a -73 dBm signal from a signal generator and do an S-meter calibration at S-9 the panadapter display using power spectral density does not read -73 dBm. What setting have I missed. TNX Tom

 

[majoco]

What does it read? Is the signal generator properly loaded by the input impedance of the SDR play? If not, you should have a 10dB pad after the sig gen to isolate the receiver from the sig gen attenuator and then add 10dB to your answer.
The "S" scale is not an official scale - if you look at the cal procedure for a number of receivers you will find different settings!

 

[LC_at_hdsdr_dot_de]

I am using HDSR 2.70 with SDRplay. When I input a -73 dBm signal from a signal generator and do an S-meter calibration at S-9 the panadapter display using power spectral density does not read -73 dBm. What setting have I missed. TNX Tom

Hi Tom,

the S-meter and spectrum are different things.

* The S-meter does show the integral (or sum) of power over the frequency bins within the selected modulation's bandwidth. So you get the power of signal (+noise).

* The spectrum does just show the power of one single FFT bin - normalized to 1 Hz in PSD.

The problem is, that the RBW is never suitable for an unmodulated carrier from a signal generator. This is, cause an unmodulated carrier has effectively NO bandwidth. Whatever RBW you select, that PSD spectrum will change it's reading because it assumes that the whole FFT bin has signal. But this is not the case.
For noise (or a modulated carrier (PSK)) you can see, that the PSD reading is constant - independent of selected RBW.

Also see https://sites.google.com/site/g4zfqradio/hdsdr-signal-measurement



kind regards,
LC

 

[W0IVJ]

HDSDR S-Meter

Thanks for the responses. I will follow all the suggestions. Tom