Using his Rig Expert as a source, spec'd to put out +13 and
adding 60 dB of attenuation the RPI/Kiwi indicated -43 dBm at
15.092 MHz, about 4 dB high of what it should. I managed to sweep
it to 30 MHz one time and got this data:
Because we don't yet know the error v frequency and only hope the
Rig Expert + attenuation is correct at 15 MHz, it's too soon to
draw conclusions but at least at 15 the noise (with the 3-4 dB
correction) would indicate arounbd -157 to -158 dBm/1-Hz in the
absence of strong signals which is exactly what the 'standard'
Kiwi normally measures. We didn't test to see if there was also
noise floor lift in the presence of a strong signal that exercised
all of the ADC bits and thus might expose non-linearity.
The code in the Kiwi or WebRX has issues that appear to relate
to the 60 MHz span. I had to zoom to max and back to get the
display to be right.
I don't know what the spectrum of the Rig Expert, 2nd and third
harmonics of what is probably an SiLabs synthesizer seem normal
but I am suspicious of the non-harmonic term shown at 49+ MHz, It
may be aliasing. Maybe they didn't get the filtering right:
That's all for now, an attempt to measure noise to 60 MHz failed
with kiwirecorder.py not getting response after the first success.
Don't know why not.