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Originally Posted by GravelChan  I don't quite understand the problem people are having with VHF signals except perhaps with an indoor antenna in a urban setting. I'm in south central South Dakota and pick up 10 and 13 which are 58 miles north, and channel 7 which is 59 miles south with 90-100 signal strength. Also a UHF channel 19 about 60 miles north. These antennas are at 50' which of course helps.
Cut channel 13 and separate UHF antenna pointed north with a 7777 amp. So I'm picking up channel 7 (NE PBS) off the back of these antennas with 90-100 signal strength.
However, I have a friend west of me that has an antenna similar to your grandma's mounted in his attic (no amp) that picks up these same channels. The signal strength isn't what mine is but they do lock in fine. |
Signal strength means nothing to us due to the fact that there is no standard SWR - standing wave ratio between receivers and what is considered to be a strong signal by one manufacturer is not as good by another manufactures standards. What matters is the sensitivity of the receiver. In the old days it was determined by the quality of the first transistor in the front end of the receiver.
By determining what you have in your link budget, line loss, splitter loss, antenna gain, amplifier gain, free space loss, what ever is in your first and second fresnel zone and the power of the transmitter and the distance between the transmitter and the receive antenna - you can figure out how much signal is being received at your location.
Attic antenna's is a poor comparison due to the fact that although wood is not opaque to UHF signals, the building materials such as aluminum is. A piece of aluminum 6 inches wide between the antenna and the signal can be enough to block your signals. A vent stack in the attic will not block your signals, but the moisture inside of the pipe can. The same holds true with shingles. The shingles and plywood and trusses might not block your signal, but the moisture in the wood and the moisture under your shingles will.
You can loose 6 db or more just through the wall. Although this might be a acceptable amount of loss in a urban area, in a fringe reception area, it might be the difference between watching a television station and no reception at all.
With a digital signal, you can loose 70% of the signal and still have a good signal. BUT - once you loose 70% of the signal, anytime something comes between you and the signal you will experience drop outs. Be it rain, snow, fog, a airplane, a flock of birds, a swarm of bees, leaves in the trees, evergreens which never loose all it's needles at the same time etc.
Front to back is not a real reception term, it is just a generalization to explain how a antenna works and what you need to take into account when designing equipment for proper reception. If a antenna has a high front to back ratio, it also has poor rejection qualities and with a digital signal, it could cause more problems then it solves. Analog signals - you would experience ghosting - due to two of the same signals reaching the tuner at the same time. With a digital signal - it is all or nothing. The information that the tuner receives is all ones and zero's and when you corrupt digital information - it is worse then not having any information at all.
Like scratching a CD and then trying to play it in a CD player.