WSPR - a peculiarity.

Seaside WSPR, 16/09/19, Anglesey west coast.

Just as I was getting ready to do some more analysis on seaside operating with WSPR, I came across an interesting anomaly.

To my simple mind, if one increases the output of a transmitter by 7dB (1W to 5W), then the improvement in signal strength at the receiver might be expected to be of a similar order.

But in using a reference station - G0CCL - with which to compare my own results, I found that increasing the power by 7dB resulted in a quite consistent 13dB improvement at a distant receiver (in this case, US receivers).

G0CCL is operated by quite experienced electronics whizzes, so I doubt that the power outputs are not correctly set or indicated - though it's always possible and I have asked them to check.

If anyone has any ideas, I'd be interested to hear of them under 'comments'.  One idea from elsewhere has been that noise may vary at the receiver.  That may well be true, especially as the overwhelming majority of receivers are in noisy environments where noise may vary substantially.  The proof of this idea must be to select a station like DP0GVN as a receiver in future work.  I noticed that, when I chose TF4M in a remote and RF-quiet part of Iceland, changing the output by 7dB resulted exactly in a 7dB change in received signal strength.