Flatness of KiwiSDR response < 500 kHz?
I'm finally chasing down local LF noise sources. With virtually every grid load being a nonlinear device of some sort these days it seems almost hopeless, but I have to try.
One major offender in my shack is an APC BACK-UPS XS1500. Interestingly it's actually quieter when running on inverter and disconnected from the wall; the battery charger that cycles on and off to keep the battery topped off seems quite noisy. It switches at 71.5 kHz, and while I can see a line there in the KiwiSDR waterfall its harmonics appear MUCH stronger.
It could simply be antenna rolloff (I'm using an untuned G5RV for this testing). But I'd like to know the nominal frequency response of the KiwiSDR below 500 kHz or so; I don't have a calibrated signal generator to find out. Thanks!