HDTV Antenna

An HDTV Antenna is a new way to say TV antenna. That's right, in the old days; we had black and white television. In order to watch television back then you needed a 'TV Antenna". The antenna could be a simple antenna for stations that were powerful and were close by in the same city or town. The farther the stations transmitting antenna was the better the antenna you needed. Some antennas back then required a big bulky antenna, and usually rated as how many elements it had and how far it would go. The big antenna was probably an all channel antenna. It had big long rods (elements) on one end and shorter rods (elements) on the other end. The longer elements were for VHF Channels 2 through 6. The next shorter elements were for VHF channels 7 through 13. The real small ones were for UHF channels 14 through 83. Now let’s examine the antenna a little closer so you can see the whole picture, ha, ha. The radio wave traveling in the air cannot be seen, with the exception of light, but even then you cannot tell where it starts or ends. Like a jumping rope you move it and it goes up and then it goes down. From the point it starts up to the point it starts up again is called one cycle. If you could measure from one end to the other that would be the wavelength. Formulas for figuring this out is based on the speed of light. Simply put a wavelength is velocity divided by the frequency. Enough of that for now, let’s move on. Just how many of those cycles that happen in one second are measured. If it was only one then it would be one “Hz” (1Hz). Named after a German Physicist Heinrich Hertz this is just another way of saying cycles per second. TV Channel 2 covers a frequency range of 54 MHz to 60 MHz. “M” stands for Mega or million, and as you can see is 54 million cycles per second. All antennas work from a formula that gives the proper length of an element, for its corresponding frequency. They are usually cut to a length of some 1/4, or ½ wavelengths. For an example let’s just calculate 54 MHZ to see what it is for a ½ wavelength. 468 divided by 54 equals 8.67 feet. The 468 in the formula is a constant value that you use each time you calculate for finding the length of a ½ wavelength; I will not go into detail here why that is so. Since I used the formula for finding the length from one end to the other or one side to the other side, you can see that it is a large size element. Just to clarify this, it is 4.3 feet each side of the boom, the structure it is mounted to that holds the elements in place. Now let’s calculate channel 24 UHF, where the frequency is 530 MHZ; using the formula 468 divided by 530 is .88 feet or 10.6 inches. What a huge difference, so you can see how length and frequency are an important factor in an antenna. You say why does the length has to be a certain value? Well it does because when it is cut for the frequency it will resonate at that frequency. That means there will be no opposition to the electromagnetic wave at that frequency and it will catch the wave better. If that wasn’t true then antennas could look like anything and would work for everything. I am not trying to get technical here, and I know this is not the exact explanation since it does get technical, so for those who know, know it gets involved. I am trying to write this for those who do not know and am just trying to get to a point about HDTV antennas which we can now talk about.
Now that you have an idea that TV antennas and elements are cut for certain frequencies, the “TV frequencies ”, lets talk about when television went from black and white to color. Remember now the stores were selling “Color TV Antennas” to people. Who would know you would need a special antenna to receive color. Well you don’t need a special antenna to receive color television. The frequencies haven’t changed, the assigned frequencies still remain the same, the formula for making an antenna for that frequency is still the same, and it’s the same antenna. Now we have HDTV, and people trying to market it. People you don’t need a special antenna to get HDTV; you just need a TV antenna. If you have a simple antenna it will pick up stations up close where a more sophisticated antenna will pick up stations farther away. If the signal is not received well enough on HDTV it will not work at all or will try to and you will see the picture for a second and it will freeze then go away and then do it again. The old TV signal that we are getting away from, you could see the picture and watch it get better as the antenna is turned toward the transmitting antenna or in case of Rabbit Ears antennas you would have to move it slightly one way or another and spread out the ears etc. If you are in the city simple rabbit ears might be all you need, but if you live in the country, you might need a better antenna to see anything at all. When HDTV becomes all you can get then you will not know if you can get it or not unless you have a really good antenna system, if of course you live in the country. Inside city dwellings you might get reflections off of objects so true direction of transmitting antenna might not be known.
In July of 09 we will take a look at building HDTV antennas from scratch. We will start with a basic antenna then move on up to more powerful antennas. Why pay for something when you can make it yourself and have something to show your neighbor who pays for all his stuff.