As a VPR listener you know there are a myriad answers to that question, but today, it’s all about two words:Tropospheric propagation.
I should back up. We got this email from a listener over the weekend:
I was listening to A Prairie Home Companion and I got a lot of static, which happens occasionally on 88.7. I caught the call letters of the interfering station, WAGP 88.7, Christian Radio from Beaufort, SC serving the Savannah, GA area with 100,000 watts. I live in Porter Corners, NY on the first rise of the Adirondacks at 1000' elevation. This is amazing reception for FM. I just thought you would like to know.
Might seem strange, but this is actually an annual phenomenon, according to Rich Parker, VPR’s director of engineering: This time of year always brings reports of reception of distant stationsin various places around the country. In case you would like to know more about this phenomenon, there is an excellent article on WikiPedia here.
Radio is so cool!
Hi Michelle!
ReplyDeleteI hate to be a nitpicker, but it's actually much more likely that the phenomenon your Porters Corners listener experienced was "sporadic E-skip," rather than tropo ducting.
Think of it as the difference between a mirror and a tube: in e-skip, a layer of the ionosphere becomes charged, and rather than allowing FM radio waves to pass out into space unhindered, it acts like a big mirror, reflecting those signals down to another spot hundreds of miles away.
Tropo ducting, by contrast, creates what amounts to a tube that carries the signals long distances between temperature-inversion layers of the atmosphere, generally much lower down than the areas where E-skip occurs.
Tropo ducting can do anything from enhancing semi-local reception to carrying signals several hundred miles; I've received VPR on 107.9 here in Rochester NY, 300 miles away, via tropo ducting. It's very closely related to local weather conditions, and is most common in humid weather and in coastal areas.
E-skip is less dependent on local weather, and generally brings in stations no closer than about 600 miles away and no farther out than about 1500 miles.
Either way, there's not much you can do when it happens (whether you're a listener or a broadcaster) than to sit back and see what else is coming in!
Scott Fybush
NorthEast Radio Watch
(and occasional consultant to VPR!)
Hi Scott,
ReplyDeleteThanks for the explanation of sporadic E-skip!