True dBm values for RTL SDR power measurements

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Mike433
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Joined: Thu Sep 25, 2014 7:37 pm

True dBm values for RTL SDR power measurements

Post by Mike433 » Wed Jul 22, 2015 6:32 pm

Hi
As far as I understood the way the RTL-SDR dongle works regarding the power measurements is that it provides relative dB measurements between the signals (in the case of rtlizer by Alexandru Csete it is reported in dBFS).
However, I have seen some software products out there which report the values in dBm, how are they doing that?
Are they doing a pre-calibration or what?

Thanks in advance.
Mike.

rtlsdrblog
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Re: True dBm values for RTL SDR power measurements

Post by rtlsdrblog » Thu Jul 23, 2015 12:22 am

Which software are you referring to? I believe that with the RTL-SDR pre calibration is needed if you want dBm.

Mike433
Posts: 3
Joined: Thu Sep 25, 2014 7:37 pm

Re: True dBm values for RTL SDR power measurements

Post by Mike433 » Thu Jul 23, 2015 8:26 pm

There are couple of S.W. out there, that are showing the readings in dBm, for example SDR-Sharp does the reporting in dBm. So my question is how are they doing that? Are they doing someform of pre-calibration or there is a way to directly relate the readings from the usb dongle to dBm.

Thx.

AGL Bob
Posts: 1
Joined: Tue Aug 04, 2015 7:29 pm

Re: True dBm values for RTL SDR power measurements

Post by AGL Bob » Wed Aug 05, 2015 1:32 am

Mike,
If you are using SDR# you can go into the SDRSharp.exe.config file and change the fftOffset value. I changed mine to -107 and it came out correct at 800MHz using a sig generator. Also, you need to turn off both RF AGCs and set the RF gain to 29.7 dB under the menu options.
http://forums.qrz.com/index.php?threads ... er.391657/

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