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Question, Please!!
- Thread starter BIGSTICK
- Start date
All technical questions should be directed at Jabba17's daughter.
bnaivar said:So I guess the answer is "It's not supposed to". :-\
No, the answer is 'no'. No part of an FM antenna system is part of the ground like an AM's is.
IIRC In microwave and radar (a FM signal at much higher frequencies) terrain (the dreaded multipath) temperature inversions, sometimes a large body of water with waves will “fool" some radar, and antenna height due to the “curvature of the earth” are the limitations. I lost my engineering manuals in a move several years ago, but IIRC I never saw a where ground conductivity number entered into and FM equation. It would be interesting to set up a FM transmitter to run at an AM (540 -1710k) frequency just to see what happens. That would be a vary large bay on the antenna. I wonder if it would cut out some of the interference?
secondchoice said:It would be interesting to set up a FM transmitter to run at an AM (540 -1710k) frequency just to see what happens. That would be a vary large bay on the antenna. I wonder if it would cut out some of the interference?
An FM transmitter will not run at those low frequencies. Tube type transmitters, the tube cavity is built and tuned for the high frequencies. And solid state transmitters, the MOSFET and other amplifier devices along with the combining devices are designed for VHF frequencies and will not operate at the low AM frequencies.
For what it's worth, the FM antenna could not pass the AM frequencies. It's too short. The cost to build an antenna to operate at AM frequencies would be prohibitive.
BRENT said:Does ground conductivity have any effect on FM signals?
No sir. You will observe that most FM antennas are located on tall towers (some share a candlelabra) to take advantage of line-of-sight, while most AM towers are in low-lying marshy places to take advantage of ground conductivity. Most AM towers have an extensive built-in "ground system" radiating out from the base; FM antennas don't need it. You need quite a bit of land for AM (ie: Cheshire Bridge 790/920/970/1190) while you go for the height for FM (ie: Richland Hill).
I could go on ..... but then I would expose my ignorance. ;D
Yes, and 1690 is also located at AM Transmitter Heaven on Cheshire Bridge Road.
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