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JB Antennaman · 06-19-2009, 10:32 PM

You can only amplify a signal if a signal is there. A amplifier cannot produce a signal when none is present.

You have to remember that there is always signals around you, just that very few of those signals are television.

In the analog days there were two effectively transmitters for the TV
station. A transmitter for the video and a transmitter for the audio.
The video transmitter was Amplitude Modulation see
http://en.wikipedia.org/wiki/NTSC

The audio was FM at a much lower power.

The reason that the video was a higher power is that AM is more susceptible to noise requiring a stronger signal at the receive and a higher power output of the video transmitter

http://en.wikipedia.org/wiki/Television_station
"In North America, full-power stations on band I (channels 2 to 6) are generally limited to 100 kW analog video (VSB) and 10 kW analog audio (FM), or 20 kW digital (8VSB) ERP.
Stations on band III (channels 7 to 13) can go up by 5dB(W) to 316 kW video, 31.6 kW audio, or 63.2 kW digital.
Low-VHF stations are often subject to long-distance reception just as with FM.

There are no stations on channel 1.

UHF, by comparison, has a much shorter wavelength, and thus requires a shorter antenna, but also higher power.
North American stations can go up to 5000 kW ERP for video and 500 kW audio, or 1000 kW digital.
Low channels travel further than high ones at the same power, but UHF does not suffer from as much electromagnetic interference and background "noise" as VHF, making it much more desirable for TV. Despite this, in the U.S., the FCC is taking another large portion of this band (channels 52 to 69) away, in contrast to the rest of the world, which has been taking VHF instead.
This means that some stations left on VHF will be harder to receive after the analog shutdown.
Since at least 1974, there are no stations on channel 37 in North America for radioastronomy purposes."

UHF communications are more "line of sight" communications than lower frequency VHF. It is sort a like having a sound vs a light.
If you make sound it radiates in all directions, around buildings, through walls, down into holes (valley).
Shining a light does not go around corners or through walls, and if it is a pinpoint light it doesn't go down into the valleys.

The earth is round and eventually the beam of light, UHF tv the beam will no longer touch the earth but go up into the sky.
Here is some information concerning line of sight and how it effects TV
http://www.softwright.com/faq/suppor...re_values.html

http://www.ian-ko.com/ET_Surface/Use...Discussion.htm

http://en.wikipedia.org/wiki/Horizon

The height of the transmitting antenna is factored into the power output of the TV station.
The power output for TV & FM is rated in ERP (Effective Radiated Power)
There are a number of factors the go into this calculation.
Several Key items are:
Height of Antenna. listed both as HAAT (Height Above Average Terrain) and AMSL (Height Above Mean Sea Level)

Gain of antenna: Just like your receiving antenna has gain in db so does the transmitter.
Remember 3db gain is equivalent to doubling the output power. or 1/2 the electric consumption expense.

06-19-2009, 10:32 PM	#6
JB Antennaman Mork from Ork Join Date: Jun 2009 Posts: 567	You can only amplify a signal if a signal is there. A amplifier cannot produce a signal when none is present. You have to remember that there is always signals around you, just that very few of those signals are television. In the analog days there were two effectively transmitters for the TV station. A transmitter for the video and a transmitter for the audio. The video transmitter was Amplitude Modulation see http://en.wikipedia.org/wiki/NTSC The audio was FM at a much lower power. The reason that the video was a higher power is that AM is more susceptible to noise requiring a stronger signal at the receive and a higher power output of the video transmitter http://en.wikipedia.org/wiki/Television_station "In North America, full-power stations on band I (channels 2 to 6) are generally limited to 100 kW analog video (VSB) and 10 kW analog audio (FM), or 20 kW digital (8VSB) ERP. Stations on band III (channels 7 to 13) can go up by 5dB(W) to 316 kW video, 31.6 kW audio, or 63.2 kW digital. Low-VHF stations are often subject to long-distance reception just as with FM. There are no stations on channel 1. UHF, by comparison, has a much shorter wavelength, and thus requires a shorter antenna, but also higher power. North American stations can go up to 5000 kW ERP for video and 500 kW audio, or 1000 kW digital. Low channels travel further than high ones at the same power, but UHF does not suffer from as much electromagnetic interference and background "noise" as VHF, making it much more desirable for TV. Despite this, in the U.S., the FCC is taking another large portion of this band (channels 52 to 69) away, in contrast to the rest of the world, which has been taking VHF instead. This means that some stations left on VHF will be harder to receive after the analog shutdown. Since at least 1974, there are no stations on channel 37 in North America for radioastronomy purposes." UHF communications are more "line of sight" communications than lower frequency VHF. It is sort a like having a sound vs a light. If you make sound it radiates in all directions, around buildings, through walls, down into holes (valley). Shining a light does not go around corners or through walls, and if it is a pinpoint light it doesn't go down into the valleys. The earth is round and eventually the beam of light, UHF tv the beam will no longer touch the earth but go up into the sky. Here is some information concerning line of sight and how it effects TV http://www.softwright.com/faq/suppor...re_values.html http://www.ian-ko.com/ET_Surface/Use...Discussion.htm http://en.wikipedia.org/wiki/Horizon The height of the transmitting antenna is factored into the power output of the TV station. The power output for TV & FM is rated in ERP (Effective Radiated Power) There are a number of factors the go into this calculation. Several Key items are: Height of Antenna. listed both as HAAT (Height Above Average Terrain) and AMSL (Height Above Mean Sea Level) Gain of antenna: Just like your receiving antenna has gain in db so does the transmitter. Remember 3db gain is equivalent to doubling the output power. or 1/2 the electric consumption expense.