Myths, Magic, and Reality
One question we get every week is “when are you going to increase power, or improve the signal”. The truth is no matter how much power a station transmits, the digital carriers remain virtually the same carrying zeros and ones. If you look back at the pictures of the “haystack” signal stations transmit, you can see the business part of the signal is the small carriers on the top, that look like Bart Simpson’s hair. The receiver decodes that from left to right, not top to bottom. That haystack needs to be flat, and above the neighborhood noise, but not necessarily tall. Most converter boxes have a signal strength meter screen, but it is not signal strength most of these are measuring, it signal quality. Naturally, the higher the quality of the signal, the better the receiver can decode it. I only mention this as most people confuse signal strength versus signal quality. The quality of the signal is the most important factor, not how big the signal is, but these meters are designed to be read in the familiar way, even though they are not always as you think.
Your antenna is your key to successfully decoding the digital bits from the signal. The 8VSB used over the air has to be decoded from the flat top of the haystack. If it is tilted, or has dips and peaks in it, the receiver has a hard time decoding the data. That causes the rectangular blocks and freezing in the picture. It’s the same symptoms as being on the digital cliff, where the signal strength isn’t high enough, but you can have a strong signal, and still not be able to decode the signal.
I often advise viewers to stop thinking logically when troubleshooting RF issues. The signals just don’t behave the same as analog technology to interference and indoor walls causing bounces. You have to have a “clean” signal, without multipath. That’s where signals bounce off walls and buildings, and arrive at the antenna a little bit later than the main signal. I demonstrate this in my video “House Call” where Dr. Mark Vardy and I compare the packets of data to the human spine. Well, I thought it was cleaver, and it does show what happens with most indoor antennas.
You want quality over quantity for good stable reception. Certainly, if the signal dips in and out, it is not going to be satisfactory. As long as your antenna gets the signal consistently, your receiver should be able to display perfect pictures.
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Comments
Nothing is different affecting anyone at 17 miles except frequency. It’s a function of the antenna and receiver. There may be something in the line blocking channel 55 like an amp or splitter, and surely they can block one channel and pass others. Is your receiver mapping us to 55-1 instead of 17-1? I’ve heard from some users of a certain brand of box having this issue, but not widespread.
It is not the mapping, so it must be something in the distribution system (Channel Plus 3025). I have tried to get 17.1 on two different HD televisions, and I have tried mapping 17 to 55.1 manually on both TVs, but no luck. I understand blocking frequencies above or below a certain point, but it seemed odd to me that I can get 52 and 57, but not 55. That seemed to be a more selective block than I would have thought possible. If I could not get 55 or 57, then I would have thought there is something in my system that is blocking high frequencies, but since I get 57 just as well as I get 52 and lower, I was confused.
I’m afraid common sense does not work with antennas and RF. It is very easy to create a single channel trap with a simple piece of wire on a splitter that is not terminated. If the wire length matches the wavelength, it can filter that frequency and pass others. We have ti use filters in our transmission lines to block harmonics from interferring adjacent channels.
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I understand what you are saying, but I am still confused as to what is different about 17.1 from the other digital channels. I live 16.9 miles from your transmition tower. As I understand it, until the switch, 17.1 is on channel 55. I can receive 28.1 (temporarily on channel 27), 22.1 (channel 57), 5.1 (channel 48), and 50.1 (channel 49), all of which transmit from the same tower as 17.1 and on frequencies both above and below the frequency on which 17.1 is broadcast. I can also get 11.1 (channel 52), which is on a tower that is less than 2 degrees of separation from the tower from which the other stations broadcast, and I can get 4.1 (channel 25)off the backside of my antenna (i.e., about 180 degrees from where the antenna is pointing), but I cannot get 17.1. What is different about 17.1, and will it improve after the conversion?