On Jan 24, 2009, at 10:59 AM, Stephen W. Kercel wrote: > If you look > at multi path propagation at HF radio waves over intercontinental > distances, and suppose that your two receivers were responding to two > different signals taking two different paths, the differences in > time of > arrival of the different signals would be 1/10000 second or less.
Sounds right. The ITU-R 1487 Recommendation for HF channel simulators has some numbers on path differences, and none showed more than 7 milliseconds. For low latitude quiet conditions, the ITU recommendation uses two paths, with a mean delay of 0.5 milliseconds. For disturbed conditions, the mean delay is 6 milliseconds. For mid-latitude quiet conditions (same as the CCIR 520 "Good" conditions), the mean delay is 0.5 ms. For disturbed conditions, it is 2 ms. For mid-latitude NVIS disturbed conditions, the relative path delay is 7 ms, the same as the mean path delay for a high latitude disturbed conditions. I went back and checked Watterson's 1970 IEEE paper (the grandpappy paper that all HF channel simulators are based on) which has some real measurements. For 9.25 MHz, they had measured relative path delays of the order of 1.1 ms for 2 hops off the F layer, 0.3 ms for 1 hop off the F layer and 0.04 ms for one hop off E layer. 73 Chen, W7AY _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
