I’m always intrigued when someone finds a novel aspect of something mundane. Almost every household in the U.S. has one or more TVs, and the average American watches more than four hours per day. But how many people know that it is possible to receive stations hundreds of miles away with an ordinary TV?
A small group of people have turned picking up signals from distant TV stations into a sport. It’s called TV DXing. (“DX” stands for “distant.”) Many TV DXers are amateur (ham) radio operators; some also hunt distant AM and FM radio stations. There is even a Worldwide TV-FM DX Association. The record for VHF reception is over 10,000 miles (when a British TV station was received in Australia); UHF DX distances are much shorter.
Successful TV DXing is mainly a matter of knowing when (time of year/time of day) and where (over-the-air channels) to look. It is possible to receive TV stations from other cities using a “rabbit ears” antenna. However, a directional rooftop antenna with a rotor will do even better. There are also plug-in cards that add analog and even digital TV reception to PCs, making it easy to capture, store, and share images from distant stations.
Here are some screen shots provided by St. Louis area TV DXer Eric Bueneman (amateur radio callsign NØUIH):
What makes TV DXing possible? The FCC assigned the VHF and UHF bands to FM radio and television because signals at these frequencies normally do not travel long distances. However, certain atmospheric conditions enable the signals to travel much further than usual. The three main sources of DX propagation are sporadic E, tropospheric ducting, and meteor burst.
Sporadic E propagation occurs when signals reflect off patches of highly ionized gas in the E layer of the ionosphere. It is less common than skywave propagation, which accounts for worldwide shortwave reception, but it affects higher frequencies.
Tropospheric ducting is the result of atmospheric temperature inversion and causes signals to bend (refract). It is most common in the summer and fall and typically enables signals to tunnel through the atmosphere up to 800 miles.
Meteor burst occurs when signals bounce off ionized gas trails left by meteors. Tiny meteors collide with the earth's atmosphere almost constantly. Propagation may last from as little as a fraction of a second up to several minutes. (Believe it or not, during the early 1990s at least one company offered meteor burst communications for long-haul truck fleets.)
The conversion to digital TV will affect TV DXing. Say good bye to TV channels 52-69, which are being reallocated to other services. DXers should be able to capture more perfect or near-perfect video frames, but digital transmission (which tends to be an all-or-nothing affair) is more intolerant of multipath propagation.
I believe the FCC’s forced march to digital TV could be a big problem for consumers using “rabbit ears” antennas for local reception, and that will be the subject of my next post.