Lately I've taken an interest in antennas and long distance signal reception, so I thought I'd discuss that a little bit. Being in Statesville, I'm in a pretty good location to receive stations in multiple broadcast markets. Technically, Statesville is in the Charlotte market, and most of the towers are about 40 miles due south. But in the 50 to 60 miles range are channels in the Greensboro market. I can receive both sets of channels nearly perfectly (except, of course, WGHP-8), but there's nothing really exciting about that. Where the fun comes in is trying to receive more distant channels.

The rule is that if your TV antenna can't "see" the broadcast tower, then you can't receive the channel. But all rules are made to be broken, and that's where it get's interesting. Because of the natural curvature of the earth, the standard transmission range is about 60 miles; beyond that, the horizon interferes with the "line of sight" between the tower and the antenna. So, generally speaking, the higher you get your antenna, the better your chance of receiving a distant signal. However, a few feet usually won't make much of a difference. The weather plays an even more important role because it can actually bend the radio waves to allow them to travel along the curvature of the earth and propagate further. This often happens at night when relatively warm air is trapped at the surface and relatively cold air settles in above it. This phenomenon is known as "tropo" (because it happens in the tropospheric layer of the atmosphere) and it pushes the signal down delaying it's eventual escape into space.

Tropo can be interesting. Last year -- while standard analog signals were still in use -- I was flipping through the channels and landed on channel 4. The picture was fairly clear, and in the corner of the screen I saw a CBS logo. I knew there was channel 4 in Chapel Hill and another in Greenville, SC, but neither of them are CBS affiliates. After about a minute I heard a commercial for a local business in Miami, FL, and after a quick search online I confirmed that I had received WFOR-4 in Miami. That's over 700 miles away! I only received it that once, and I'm sure I never will again since analog is gone. But, on a regular basis I can receive stations from the Greenville, SC, market and also the Raleigh market, both of which have towers between 100 and 140 miles away.

There's a name for this addiction: DXing. With the "DX" representing the word "distance", it refers to the interest in receiving long distance radio or television signals.


This is a forecast map of the expected propagation of television signals.  Orange and red colors indicate conditions are best to receive more distant signals.