I've been Investigating spurious responses using a long wave broadcast.
Below for comment and for general interest are the results
I'm using SDRConsole (V2) Build 2381 and a new SDR-Play location BH23 8DU
The antenna is a home made loop precisely tuned to Radio 4 on 198KHz
Span=500KHz, LNA off, RF gain -40dB, Visual gain -20dB with AM setting
198KHz gives me -39dBm
396KHz gives me -75dBm
584KHz gives me -107dBm
All these readings vary exactly in line with each other as I alter the gain settings.
Switching on the LNA and readjusting for best reception RF gain -50dB, Visual gain -20dB
198KHz gives me -48dBm
396KHz gives me -83dBm
584KHz gives me -98dBm
792KHz gives me -123dBm with some distortion
Overloading and bad distortion appears with a gain setting of -35dB.
With the receiver tuned to 198KHz giving a signal of -38dBM the signal at 396KHz disappears into the noise when the loop is tuned high or low and the signal at 198KHz is -57dBm
Am I seeing effects of non-linearity in the front end of the SDR-Play?