TV DX is the way a television signal is projected through the airwaves. It's an important component of modern day television, for without it, many countries who have yet to perfect cable transmission underground would not be able to reach millions of home viewers with a television. Reception of the TV DX signal happened by accident and continues to this day to surprise the unsuspected viewer who catches a glimpse of a foreign land's television programming.
February 1938 brought forth the first interception of a foreign land's television signal. The RCA Research Station in New York picked up a trans-atlantic signal from London. While checking the area for various local signals, the station picked up a live telecast of a BBC station's soap opera. Even the BBC logo was evident on the broadcast proving that, indeed, what the researchers were viewing was from England. Since the researchers were recording at the time, they recorded the soap opera and it's been archived today as one of the only pre-war British television productions that survived.
When World War II began in 1939, the BBC suspended TV DX transmissions. This limited the capabilities of researching into the signal reception of television and FM signals involved since the whole world was on the brink of destruction. When the BBC began to transmit again, in 1946, countries as far away as South Africa picked up on the signal almost as soon as the BBC flipped the switch and began transmitting. This became a concern for the United States, who knew that any type of transmission being sent on that frequency had the potential to be picked up by anybody else in the world. This was the same reason the BBC suspended transmission during the war, they didn't want communications to be intercepted by the wrong hands.
This type of transmission triggered the United States Federal Communications Commission (FCC) to allocate a particular band for TV DX transmissions. This was both to limit the range of transmission as well as to prevent other transmissions from interfering. Since interference can lead to problems with communications as well as entertainment, limiting the scope of transmission band was the easiest way at the time to prevent problems from arising. The FCC limited transmissions to 42 to 50 MHz for broadcasting. However, even though limiting the band frequency was theorized to stop interference, it soon became apparent that this wasn't going to be enough. TV DX and FM radio station signals from as far away as 1,400 miles were cross-referencing with local signals in sporadic areas. While this only happened once in awhile, usually when the weather acted up, it soon became a problem for local stations who had to take calls from viewers who couldn't watch the nightly news.
By 1945, the FCC changed the band that FM would need to broadcast on to 88 to 108 MHz. It seemed that, officially, the changes were made because of co-channel interference, atmosphere effect on signals and the current range of coverage as television expanded through the country. While this improved the strength of signal in many areas, problems still arose when the weather took a turn for the worse. No matter what you do to prevent crossing signals, it's bound to happen.
TV DX hit a world record in 1957. One particular signal was picked up more than 10,000 miles from its initial broadcast point. England's BBC was picked up in southern Australia. Since then, signals have triangulated from all over the world and viewers have surprisingly picked up on the invasion on their televisions. Throughout the world, everyday, signals are crossed all over the place.
As long as TV DX is broadcast through the air, viewers will be exposed to the cross-interference of two or more television signals. As more companies opt to broadcast their signals through coaxial cables in local areas through a central hub that later connects to a larger one with a production signal, viewers will be exposed to this interference. When you send a TV DX signal through the air, there's no telling where it will end up. The next time you come across a television show that just doesn't seem right, you might be in the middle of trans-continental television signal getting misplaced.
