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Participants: ISS - East Elementary School |
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| WLOS TV Tower - How TV Comes to You !
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| Glenn
Gurley: It is great to have Norman Harrill with us this morning. Norman do you have some opening comments before we
ask questions? What will your focus be this
morning? Glenn Gurley: Welcome Iredell County!!! Norman Harrill: Howdy from the top of Mt. Pisgah at the WLOS broadcast transmitter site - 5,700 ft. above sea level with great views of WNC. Transylvania Count: Good morning Mr. Harrill from TC Henderson and Pisgah Forest Elementary! |
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Norman
Harrill: The WLOS transmitter is approximately 350ft high.
There are actually 3 stations (2 TV and 1 Radio) broadcasting from up here - WLOS
TV, WUNF (Public Television), and Kiss FM 99.9 radio. The building we are in is 3
stories high built into the side of the mountain - made of rock. Transylvania Count: Which TV stations? Norman Harrill: The TV stations broadcasting from here are WLOS TV and WUNF TV (which is UNC TV - public television). |
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Norman Harrill: Mr. Harrill is an expert in the field of broadcast television - RF transmitters - very high powered transmitters. Norman Harrill: Good morning Iredell! Glenn Gurley: How are radio waves produced? Norman Harrill: Do you mean radio as in car radio or television signals? Glenn Gurley: I mean the waves transmitted for the radio stations that are picked up in our cars and home stereo systems. Norman Harrill: A television (or any type of radio signal) starts as an electronic vibration which will become a carrier to transport the sound and picture signal from the transmitter to the receiver. Norman Harrill: To be very specific, you can study Ohm's Law.Norman Harrill: For Channel 33 (WUNF), the signal strength is 5,000,000 watts. For WLOS TV the signal stregnth is 175,000 watts. Transylvania Count: So is that why channel 33 will come through better on our TVs than other stations? Norman Harrill: As to why Channel 33 comes through better - the amount of energy used to broadcast the signal does not determine the signal clarity (i.e. how it good it looks on your tv) Rather, it takes more energy to broadcast a signal at a higher frequency than to broadcast a signal at a lower frequency. Norman Harrill: As an example - WLOS uses a lower frequency to broadcast at than WUNF. WLOS's coverage area is 6 states. WUNF's signal (a higher frequency) does not have as great a coverage area despite being a higher-powered antenna. |
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Transylvania Count: This sounds very complicated! Transylvania Count: But very interesting! Transylvania Count: When you say WLOS coverage is 6 states, does that mean you could pick it up without a cable provider. Norman Harrill: Yes, that is correct. Transylvania Count: How does it recognize the difference (radio vs. TV)? Norman Harrill: How does it tell the difference - TV waves are more complicated that radio waves. |
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Glenn Gurley: That brings another question... what is the difference between radio and TV waves? Norman Harrill: TV and radio waves use different types of transmitters. Pictures are AM modulated signals and sound is an FM modulated signals. Norman Harrill: The term modulation means putting the information you want to transmit from one point to another onto a carrier signal. Glenn Gurley: Iredell County: We are participating with a group of third grade teachers at East Elementary. We will be posting questions to you. Shirley Corcoran: With all the waves being transmitted from the various stations what keeps them from getting mixed together? Glenn Gurley: Excellent question Shirley! Norman Harrill: Signals do not get mixed up because the signals are different wave lengths. Higher frequencies have shorter wave lengths - and the TV knows the difference in how to interpret them. |
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Shirley Corcoran: How far can the signals travel and you still have the complete picture on your TV? Transylvania Count: When we lose our signal in our homes -- is that our local provider's problem? Norman Harrill: Transylvania - if you are on cable and lose the signal, yes it most likely is the local providers fault. If you have an antenna - you can check to see if the station if off the air. |
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Norman Harrill: The picture you see on your television signal shirley is an optical illusion. Her TV set consists of over 500 lines going left to right and a dot moving across the lines at the speed of light (186,000 miles/sec). When the dot gets to the bottom of the set, it goes back to the top to start a new frame. Frames are produced at 30 frames per second. So, really there is only one dot on there at any specific point in time. Norman Harrill: However, everything up here is duplicated (i.e. there is a backup system) so that the station will only be offline at the for 7 seconds at the most. Up here on the mountain, there are back generator for emergency power, two transmitters, two antennas, etc... Norman Harrill: The tower is not the antenna itself, rather it is a supporting structure for the antennas. The WLOS "antenna" is the tip top portion of the tower and only 60 feet long. The WUNF "antenna" is only 60 ft. long as well. Norman Harrill: There are other "things" such as microwave antennas attached to the tower as well. Law enforcement radios and NOAH radio antennas are attached to our tower. |
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Transylvania
Count: You explained the image as an optical illusion - so this also has something to do
with the our eyes, brain, and the "Way We Work" too??? Norman Harrill: Yes, Transylvania, you are correct. |
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Shirley Corcoran: What part of the TV knows which wavelengths to pick up to get the different channels? Norman Harrill: Shirley, the RF tuner in your television is the piece that knows what to look for in the air for the television signals broadcast at different frequencies. That is what allows you to change channels. Transylvania Count: Who invented the television BTW? Norman Harrill: Television is a progression of different inventions - Allen B. DuMont, Marconi, Frost, and several others had a hand | |||
