Linearity


Allan Isaacs
 

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

Settings are:

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?

Allan G3PIY

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