[Elecraft] RE: Critical frequency

[Ron D'Eau Claire]

Quite right, Kevin. I was confusing "Critical Frequency" with "Maximum
Useable Frequency".

The Maximum Useable Frequency is, I understand, about 3 to 5 times the
Critical Frequency, but that is an estimate and it is effected by the
geometry of the propagation as well as the frequency. 

In my original post I mentioned, in passing, the Maximum Useable
Frequency and didn't realize that when Earl responded with a comment
about the Critical Frequency that he had changed subjects!

As Earl pointed out, the CF is defined by a signal being sent vertically
upward and measuring the frequency at which there is no reflection back
to the point of origin. It's normally measured with an ionosonde - a
sort of specialized HF radar set - that gives the CF and measures the
effective height of the ionosphere. 

Sorry about that!

Ron AC7AC
K2 # 1289