A few weeks ago I noticed a strange echo on Radio China International’s signal. If you scroll down a bit you can see my YouTube recording of the problem. On one of the SWL lists, there was speculation that this problem was the result of a flaw in the RCI digital studio gear. But then a few days ago I heard it again on RCI — surely the tech-savvy Chinese would not have let this kind of problem persist for weeks.
Today I heard the same effect on a very different SW station — this one an the 24/7 fire and brimstone broadcast that appears at many points on the dial. The effect is very similar to what I heard on RCI.
So OK all your shortwave gurus: What is going on here?
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Multipath propagation? http://en.wikipedia.org/wiki/Multipath_propagation 73, Jan OM2ATC
Hey Bill, very cool recording. I like the idea of multipath propagation, and started doing a thought experiment. (Warning, I know essentially nothing about shortwave propagation, and haven’t had my morning coffee yet.) The circumference of the earth is about 40,000 meters, which would mean the propagation delay to circumnavigate the globe would be about .13 seconds (say about 1/8 of a second). I didn’t try to figure out what the delay was, but it seems a bit longer than that, which means that the path would be longer than the earth’s circumference. Multiple trips? Or a long, non-great-circle duct? I have no idea. Very cool though.
May be as simple as a studio technician listening to the air monitor with a mic open. Broadcasts today get significant delay as they are sent over the internet from studio to transmitter. Yesterday WLRN-FM was 7-1/2 seconds behind. Chip Veres Technician WLRN FM & TV
Maybe they just wound their cassette tape too tightly?
To use a descriptive adjective from the late ’60s and early ’70s: trippy. You are right about long path not being logical, as the delay is about half a second. Such a long delay would imply several trips around the Earth (about 40000 kms in circumference).