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Question about AM and FM tower height.
- Thread starter BIGSTICK
- Start date
BRENT said:
With FM, it's really the height of the antenna, which is perched at the top of the tower. Many FM transmitter sites are on mountains or buildings, and the actual tower structure is very short, but the antenna is still high.
I'm of course not an engineer, but as opposed to FM, where the antenna is attached to the tower, the entire AM tower is the antenna, i.e. is hot. I believe an AM tower's height has to do with the station's bandwidth; the lower the frequency, the higher the tower. And there are different types of towers, such as half wave, which affect the height and power.
The quick answer is on FM, antenna height is important to the strength of the signal. On AM, tower height is simply matched to the station.
With FM I believe it is always somewhat of a trade off height vs power, aka HAAT. I worked at a Class A FM with our HAAT we wound up with 105 watts (not a mis-print) H/V. In the late 60's with so few FM's around it got out like gangbusters. Localed at mile away was a "grandfathered" B or was it a C FM same HAAT with 53,000 watts. It of course was definately cheaper (a term a lot of owners loved) to get the antenna up as high as possible and run a lower power transmitter.
As far as AM, nearly as important as the "stick" is your ground radial system, and if your tower happened to be in a swamp, so much the better! I worked at a station, studio/transmitter location that was flooded in 1972. we "band-aided" the 1 KW transmitter to get it back on the air, with about 100 watts, but the ground was so wet we had nearly the coverage of our 1KW in dry weather.
BTW the "band-aid" was sitting a couple of the transformers on old vinyl 33's to keep them from shorting to ground. We did a lot of pretty amazing things to get back on the air. That period fostered my saying "if it is temporary more than three weeks, it is permanent."
As far as AM, nearly as important as the "stick" is your ground radial system, and if your tower happened to be in a swamp, so much the better! I worked at a station, studio/transmitter location that was flooded in 1972. we "band-aided" the 1 KW transmitter to get it back on the air, with about 100 watts, but the ground was so wet we had nearly the coverage of our 1KW in dry weather.
BTW the "band-aid" was sitting a couple of the transformers on old vinyl 33's to keep them from shorting to ground. We did a lot of pretty amazing things to get back on the air. That period fostered my saying "if it is temporary more than three weeks, it is permanent."
An AM tower site can get to be a prety expensive piece of real estate with 360 degree radials the same length as the tower is tall.
Speaking to the original question: the "height" of an AM tower becomes its "length" when you plug it into an engineering formula to see how efficient it is in radiating it's power.
The AM tower can be down in the valley in the rich soil next to a creek or river and the AM signal will reach out quite well. I looked at an AM station once where the original owner assumed putting the tower on a hilltop was beneficial but through the years and he and the later owners all came to realize the soil make-up of the hill was hurting the station, not helping it.
As someone else pointed out, it is NOT the height of the tower alone that affect the improved FM signal reach. FM is said to reach out in a "line of sight" methodology... which needs some asterisks and footnotes... but putting your FM antenna on a telephone pole atop the highest hill or mountain in your market area will result in the better signal when you compare that with putting your FM antenna on a 600 foot tower located in a valley surrounded by 800 foot mountains.
The AM tower can be down in the valley in the rich soil next to a creek or river and the AM signal will reach out quite well. I looked at an AM station once where the original owner assumed putting the tower on a hilltop was beneficial but through the years and he and the later owners all came to realize the soil make-up of the hill was hurting the station, not helping it.
As someone else pointed out, it is NOT the height of the tower alone that affect the improved FM signal reach. FM is said to reach out in a "line of sight" methodology... which needs some asterisks and footnotes... but putting your FM antenna on a telephone pole atop the highest hill or mountain in your market area will result in the better signal when you compare that with putting your FM antenna on a 600 foot tower located in a valley surrounded by 800 foot mountains.
BRENT said:
Whatever they did to prepare the ground radials before the parking lot was laid down will determine whether the WSB location will continue to work well for years to come. I have not read anywhere that having shopping centers, warehouses or other man-made ground cover is automatically a signal killer. A nearby high-rise sign becoming Interstate travelers to a motel or restaurant can be more harmful to an AM signal that parking lot asphalt.
But the fact that WSB remains where it is does not prove or disprove that the ownership is cheap or tight. Where would they put the tower that would make it work any better than where it is? In this day and age of "not in my back yard"... do you think that even if the owner is willing to part with princely sums of cash that they could get a new tower zoned in anywhere?
In this day and age of dire predictions about the future of AM radio and that possibility that it might go the way of the Dodo Bird in the not too distant future, how much of YOUR money would you be willing to invest in a relocation if it were YOUR station?
Goat Rodeo Cowboy said:
You are 100% correct.
WSB was there long before the parking lot was there. It might be interesting to see the sale documents for the property - unless it's long term leased. I sus[pect, of they wannaq, they can dig a new set of radials into the lot.
I believe Cox owns the land under the layers of leases. Years ago, I asked the late WSB CE John Talbert what he would do if the ground system ever needed replacing. He responded, "That would be a disaster, but we'd have to just dig it up and replace it."
In Baltimore, WWIN-AM/1400 was in the Waverly Tower Shopping Center for years. But when that ground system deteriorated, it created a major problem because the stores were built over the ground system, unlike WSB, which goes to the curb. WWIN was forced to relocate and had to decrease power as a result.
In Baltimore, WWIN-AM/1400 was in the Waverly Tower Shopping Center for years. But when that ground system deteriorated, it created a major problem because the stores were built over the ground system, unlike WSB, which goes to the curb. WWIN was forced to relocate and had to decrease power as a result.
Having 10kw/day combined with little to no interference from other stations puts an expanded band AM station into a sweet spot. I was in Dahlonega scanning the AM dial yesterday around 10:00AM; the strongest signal, of course, was WDUN/550-Gainesville, and I thought the next strongest would be WSB. But, noooo... 1690 in Atlanta came in like gangbusters. Even when you can't hear the other stations on a crowded AM dial, their carriers are there, and that affects the station you are trying to hear.
Also, RF from computers and appliances seem to affect stations in the middle of the AM dial more than the low or high end (which is a smack in the face to KDKA/1020).
BRENT said:
You picked up an Atlanta 1690 in Chicago at 10 A.M.??? Or was that P.M.
trusty said:
It was not WVON, I was in Naperville. Don't ask me how it happened...
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