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.