Flutter evidence on W1CDO to EU signal

Image icon w1cdo 20M FLUTTER EVIDENCE.png64.73 KB

See the attached showing W1CDO signal as received here in EU.
The path from NM to SE France, passes near the "aurora oval" and the effects of the frequency spreading (aurora effect) are clearly visible, although it is not strong enough to affect decoding, as it was the case on K7EK 40m signal.
This explains why it is so hard for EU -stations to get WSPR spots from US west-coast stations.
By the way this screen shot was taken today with quiet geomagnetic conditions (k=1 A=1). I guess that W1CDO signal will become unreadable, with perturbed conditions.

To see how flutter and other propagation perturbations affect WSPR and other digital modes, you may try AE4JY's PathSim, a very nice and useful freeware.
I played a bit again with it while I was without Internet and it confirmed that WSPR copes with almost any propagation model, except "CCIR-flutter" and "high latitude disturbed" models, while JT65A does...