"Radio Engineer's Handbook" by Terman (1943):
There seems to be a close correlation between sunspot numbers and yearly
average of signal strength for T/A LF signals. Maybe we better catch the
This should not surprise us. We know that the best DX condx on the 1.8MHz
band occur during periods of low sunspot activity. My 1.8MHz CW QSO with
Stew Perry, W1BB, (from 9L1, using less than 1w erp) occurred in July 1964,
which coincided with the sunspot minimum.
The illustrations from Terman are exactly the same as in my 1937 (2nd)
Edition. I had considered including this material in the LF Handbook but
there were copyright issues of which I was unsure.
It is interesting that a statistical analysis of the reception of Laurie's
transmissions by John are in line with the graphs in the Terman book. It
would seem that our LF experiments have been carried out in less than
optimum conditions and that there is a lot better to come.
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