TechnoBabble

Well one of the things I will miss.

I thought that the last year of analog TV transmissions I would be knee deep in something called TV DXing soaking in the last analog TV of the United States. But alas, I seem to either not have the time or desire or the band isn't open.

What is TV DXing you ask? For the nine out of ten who have no idea what that is, it is when one actively seeks TV signals beyond the normal reception range. Some people DX (which is a shorthand for DISTANCE) AM radio, some FM radio, some even shortwave wave and yes, some even DX TV. But you say, "You can't see TV signals beyond  60 or 70 miles. Are you crazy?" Crazy? Probably. But watching TV over 100 miles? DEFFINATELY DOABLE! "How?" "Laws of Physics my dear Watson."

Each frequency has a different physical length. They react with the atmosphere in different ways. That is why you can hear AM radio signals for thousands of miles away by night but have trouble picking up a station in the next town by day and where FM has a predictable seemingly never changing 24/7 coverage area. TV also. This is called "propagation." But that predictable 24/7 coverage  isn't always true. Things in the atmosphere are never unchanging.

AM radio signals are hundreds of feet long. FM and TV signals are from several feet to less than an inch in length. These react in the atmosphere differently. The reason AM stations can be heard at great distances at night and not during the day is due to the Sun and the D Layer of the atmosphere. If you remember from your high school science class, the atmosphere is broken up into different layers as you leave the surface of the Earth. As the wavelength shortens, they react on different parts of the atmosphere. In the D Layer, the Sun's radiation causes the molecules to spread far apart and allow the long AM waves to go into space. At night, with no Sun, the molecules clump together and whah lah! You hear WABC New York here in North Carolina.

The E Layer and with less effect, the F Layers (F1 and F2) react on FM and TV signals (but not AM signals) but they are very unpredictable when they will clump together enough to form what is call "sporatic electron clouds" that will reflect radio waves. The only sign that you MIGHT get a cloud forming is if the Sun is in an active sunspot event. The increased radiation from the Sun will cause the molecules to move closer together. TV channels 2 through 6 and the FM band will react on the clouds more often than the higher TV channels, several times a week in the summer. As you increase in frequency (and TV channels) the E and F Layers have less and less effect on the signals (only a few times a summer)  and a weather phenamena called "tropospheric ducting" or alternating warm and cold layers of air, as you have in the spring and fall, will also cause FM and TV signals to travel beyond the horizon. Tropo, as it is called, acts like someone has put an air conditioning duct in the sky between layers of warm and cold air. The radio waves get trapped in these layers and literally dump out like an AC register hundreds of miles away from the transmitter. These are mostly seen at VHF channels 7-13 and UHF channels. Get a day when it has been cool at night and hot during the day and you can almost bet you will see tropo and it doesn't take a special antenna setup to DX TV either.

Oh sure, you can put up a huge tower like Girard Westerberg of Lexington, Ky has here:

who by the way holds the current record for the fartherest digital TV station received when he picked up KOTA-DT channel 2 Rapid CIty, SD on 5/26/2004 at 8:40pm at a distance of 1,062 miles over E Layer skip! Here is his screencap to provide it:

He has a website devoted to DXing of all kinds, TV, DTV and FM at http://www.dxfm.com where he has pictures of all of his TV and DTV DXing!

Or the fabulous site of Jeff Kadet http://www.oldtvguides.com/DXPhotos in Illinios with THIS setup:

Of course you don't have to have a big antenna system to DX. Rabbit ears or regular old antennas on houses will work wonders. Just check out Mike Sittel's site http://www.mcsittel.com DXing done with a roof top antenna!

For those of you who wonder what a TV engineer uses for over the air TV reception? Check out my $50 UHF Channel Master 4338 mounted on top of a Jerrold VIP-307SR VHF antenna:

It does OK for what it is!

Now I just have to find the time to play with now before next February.