Bill Hayes has been Iowa Public Television's Engineering Director since 1999, and is responsible for Iowa Public Television's transition to digital television. In a little more than a year, analog television will be shut off, and we’ll all be watching television a little differently. Visit this page frequently to get answers to your digital television questions and to read about the industry and IPTV’s transition.
Tuesday, August 26, 2008
Are You Receiving Me?
First, a simple statement of fact. Indoor reception in inherently difficult and unreliable. The reason for this is that in order to just get to the antenna, the transmitted signal has to pass through walls and windows and all of the trees and anything else that is a ground level just to get to the antenna and all of these items degrade and disrupt the signal. In addition everything in the room with the antenna is a potential source of reflection which further degrades the receivability of the signal. On top of that add to the mix that anything in the room that moves, like the viewer, the kids, the dog or the cat will also dynamically disrupt the signal and further degrade received service and unlike analog television where the picture on the screen gives you a clear indication of how poor the incoming signal actually is, digital gives no indication until the decoder realizes it doesn't have enough information to make a picture and it either freezes, macro blocks (blockiness) or goes away. So I will never recommend indoor reception or an indoor antenna.
So why then does the Silver Sensor work when I am doing demonstrations? It is pretty simple really, the Silver Sensor is a directional antenna where as rabbit ears are omnidirectional. Plainly stated the Silver Sensor receives very well from one direction at a time so in a room where there may be signal coming from all directions, it ignores them and delivers a much less disrupted signal to the receiver than rabbit ears in the same location. Directional antennas also act a little like a satellite receive antenna (dish) in that they tend to gather more of the signal coming in from a specific direction and add it all together. This is referred to as the gain of the antenna and is specified in decibels (dB) which is a ratio. In the case of most antennas, the gain specified in dB is a comparison to the directional antenna and a dipole and guess what, rabbit ears are a dipole. In the case of the Silver Sensor, it has a gain of about 6 to 7 dB compared to a dipole but don't jump the gun, that doesn't mean it is 6 to 7 times better. The way the math and physics work out, the Silver Sensor probably collect about 2.5 times as much signal as a dipole (rabbit ears) and probably as important it ignores signals coming from other directions. That is why it works better than rabbit ears. I have had people say but my rabbit ears have a 10 dB amplifier built in so that should overcome the gain improvement of your Silver Sensor. This is not entirely true because remember that dB is a ratio so an amplifier with 10 dB of gain is taking the signal coming in to the amplifier and increasing the amount of signal by 10 dB. Okay but the amplifier is after the antenna so that the signal that is being amplified in the rabbit ears has already been degraded by all of the items I mentioned above and therefore all you are doing is increasing the size of the degraded signal but the receiver and decoder still can't figure out what the message is no more than yelling at someone who doesn't understand English makes them understand.
So I can't recommend an indoor antenna with any degree of certainty because the number of things that will disrupt the service using an indoor antenna are virtually unlimited and constantly changing. I will always tell people to look at outdoor antennas as their best option. I have had a number of people tell me that they are not permitted to put up an antenna because of local restrictions. I would suggest that you follow this web link (http://www.fcc.gov/mb/facts/otard.html) and I believe you'll find that many of those restrictions are superseded by federal rules that in most cases will allow you to install an outdoor antenna, even in rental properties. So you might want to look at antenna reception again. Remember, rabbit ears work great on rabbits but not so well on television signals.
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