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I want to compare field strength with an RTL-SDR dongle or HackRF One. With comparing I mean being correct relative to one another, like if I know field strength of one in mW/m^2 then I know the other. I am pretty sure this works for a fixed bandwidth (How to Measure Signal Strength).

My remaining question is: Can I compare field strength of 145Mhzish to 900Mhzish? I wouldn't mind an inaccuracy of factor 3.

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    $\begingroup$ Sorry to say, but even measuring the relative (not absolute) field intensities of radiated e-m waves requires the use of a receive antenna with known characteristics at each received frequency, including the effects of its operating environment. Even for laboratory grade test equipment, these conditions are difficult to realize outside of a calibrated test range. Unfortunately such measurements using the antenna of an SDR dongle will have a high, and unknown amount of error, but that may not matter, for some purposes. $\endgroup$ – Richard Fry Sep 21 '19 at 13:27
  • $\begingroup$ This antenna can be adjusted in size: greatscottgadgets.com/ant500 What if I lessen my accuracy need to factor 10? $\endgroup$ – Peterilu Sep 22 '19 at 16:04
  • $\begingroup$ There seem to be a lot of people doing it nonetheless; rtl-sdr.com/… rtl-sdr.com/rtl-sdr-used-as-a-spectrum-analyzer $\endgroup$ – Peterilu Sep 22 '19 at 17:05

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