Calibration Comparison R820T - RSP1A - Signal Generator
: The picture shows a comparison of the VOLMET broadcaster at 127.6MHz, between
a RTL-SDR dongle (one of the four in the Kerberos hardware) and a RSP1A, recorded with exactly the same
values like antenna, cable, Zoom values etc.
The difference is very small given the fact that both tuners have
different design. For these displays the "Flat Top Window" HFT70 has been chosen for the FFT. According to the documentation,
it induces an error of not more than 0.0066dB, being neglectable in the measurements.
The rightmost picture shows the peak from the Signal Generator,
having been tuned to 127.6MHz with an output level of 15dB µV. As is expected, the noise level is much smaller in this case
than from "live" antenna signals.
It might be noted that the peak level is independent of the selected FFT Length, as the "Power Spectrum (PS)" display
had been selected, maintaining the peak values and changing the noise floor when changing the FFT length. This is in contrast to
the - also selectable - Power Spectrum Density (PSD) display.
The second peak in the RTL-SDR spectrum is an artifact.