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NBC did it during the last Winter Olympics. There was broadcast right until the games started and then during viewing hours they simply reduced broadcast power or otherwise made sure their broadcast wasn't very good, enough to make watching them worthless.
Right after the games were over, back to normal.
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Originally Posted by oldtrader
It is not that NBC reduced power that caused the problem. Power and quality of your picture were reduced by the sheer number of people that were watching T.V. at the time. There is only so much power as you call it available at one time. If there are fewer people running their T.V. the signal gets better. If there are more people using it, the picture quality goes down. The system is designed for average use. When all available T.V. sets are running, they are overloading the system and the picture quality goes down.
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This is just sooooooooo WRONG.
OTA broadcast DOES NOT suffer from degraded signal quality if more people watch it. It does not matter whatsoever whether there is one person watching, or 100,000,000 people watching, the signal quality will be exactly the same for everyone at the same distance from the transmitting antenna.
EM waves (TV/radio) conform to known laws, and the primary factors in signal quality are the power of the signal being transmitted, and the receiver's distance from the transmitting antenna. A secondary consideration is the existence of obstructions in the Line Of Sight {LOS} between the transmitter and receiver, such as buildings/hills. The considerations for these factors are the ERP (Effective Radiated Power) and the HAAT (Height Above Average Terrain) of the transmitting antena. The FCC (Federal Communications Commission) sets the regulations for broadcast transmitters as to ERP and HAAT according to the characteristics of several zones within the US, in order to eliminate/minimize interference from broadcasters using the same frequencies, so that the signal does not travel more than a certain distance, which (depending on the frequency, and type of modulation) is a maximum of 149.5 miles under usual/normal conditions. Some signals are limited to shorter distances.
Under optimum conditions (no obstructions of LOS), with a transmitter operating at a given amount of power, the major factor in signal strength at the receiver is the receiver's distance from the transmitting antenna. Leaving out the mind-numbing calculations (for those of us who suck at math) of Planck's and Maxwell's equations, the fundamental law of physics we are concerned with here is that a radiated EM signal behaves according to an inverse-square law- to put it simply, if you double the distance of the receiver from the transmitter, the signal strength decreases by a factor of four.
Thus, a receiver located 40 miles from the transmitter will measure a signal 16 times lower than a receiver located 10 miles from the transmitter.
The number of seperate receivers using seperate antennas makes absolutely no difference at all to the signal strength at any other receiver. The only time the number of receivers is an issue is when using a closed, bandwidth-limited system such as cable or a coaxial distribution system using a single Master Antenna. In the case of a MA distribution system, the proper way to connect is to amplify the signal at the point where it enters the distribution box, this will increase the signal levels available to account for the drain of multiple receivers.
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Originally Posted by wordsmith680
I will disconnect TV now that the troops have been here for t-day. Charter will now charge me $40.00 to reconnect next year. Many of us, especially in rural areas have no choice of providers. I would have to cut a bunch of trees to have line of sight for satellite options. We have no option for over the air digital broadcast. We used to get about 2-1/2 channels before digital wiped us out.  ( you must be within about a 70 mi radius for digital reception) |
This is technically incorrect. It would be [almost] true if both the transmitting antenna and the receiving antenna were at ground level, at which a distance of 80 miles would eliminate LOS due to the curvature of the Earth. However, by raising the height of the transmitting antenna and the receiving antenna, this distance can be increased.
At these extended distances it is true that signal strength is substantially reduced (according to the inverse-square law mentioned above), but there are several other considerations by which a useable signal can be obtained if the transmitter is not too under-powered. The signal itself is NOT 'digital', it is still an electromagnetic wave just the same as it always has been, this cannot be changed. The only thing that has changed is the method by which the data carried by the wave is encoded. (The horsepuckey that a 'digital' antenna is needed to receive the 'digital' signal is completely false.)
To optimize reception at extended distances, one needs to raise the entenna as high as possible, use an antenna that is tuned to the frequencies to be received, and to amplify the signal between the antenna and receiver. The main issue with digital reception is that there is a much sharper cut-off point at which the signal is useable. With the old analog receivers, signal degradation would be perceived as 'snow' (visible) and hiss (audible), which, although somewhat annoying, would result in a continuous though degraded picture and audio, tolerable, if you wanted to watch it bad enough.
With the digital encoding though, signal degradation results in data loss, and, lacking the data to decode, the receiver exhibits blocky pixelation and audio cutouts. The digital data requires a better signal-to-noise ratio than analog modulation. In-line amplification can improve the signal but there are certain limitations. One is that the amplifier is indiscriminate, and it amplifies noise as well as the desired signal. Another limitation is that the amplifier itself will introduce additional noise, and the receiver must be able to discriminate between the noise and the desired signal. Receiver quality matters here, and when the receiver is unable to determine the signal from the noise it causes the 'no signal' message to appear. Some receivers are better than others. A directional antenna that can be rotated is handy too.
Also, some amplifiers are better than others. You can get cheap ones for five or six bucks that will do the job if you are close enough, but for more extended distances more expensive Low Noise Amplifiers (LNAs) are required- these inject less noise into the system than the el-cheapos. I currently have 3 cheap amplifiers in-line, which is almost sufficient without introducing too much noise, the one exception is the bonehead engineer at a particular station who (apparently) is completely ignorant of the laws of physics as applied to EM waves- he seems to have had the [completely false] impression that the change to 'digital' meant that he could decrease his ERP from 15Kw to 3Kw with no loss in quality to the further receivers. He needs a dope-slap.
There is a company called Wineguard that makes some very good antennas and amplifiers. At some point, I'll put up one of their antennas and install a couple of LNAs.
As it is, just with OTA broadcast I get more TV than I have time to watch. I currently have two HDD DVRs (with receivers), two combo DVD/VHS recorders (one with receiver, one without) and two VHS VCRs (analog receivers). The combo DVD/VHS with no receiver and the regular VHS recorders are hooked into external receivers. We just record whole series and dump them to DVD disks, maybe someday we'll have time to watch them...we're only two or three years behind at the moment.
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