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FM power in different areas
- ZenithCKLW
- Posts: 849
- Joined: Sat Nov 13, 2004 11:21 am
- Location: Livonia, MI
FM power in different areas
I went down a rabbit hole today, and noticed that the commercial FM's in Chicago mostly all have an ERP of just a few thousand watts. Detroit commercial FM's, in comparison, are mostly between 15,000-50,000 watts, with a few even more than that.
What is different about these areas that have such a difference in average ERP for commercial FM's?
What is different about these areas that have such a difference in average ERP for commercial FM's?
Re: FM power in different areas
The difference is that the Chicago stations are on very tall buildings, Sears/Willis and Hancock/Whatever, and have to reduce to an “equivalent” ERP for their Height Above Average Terrain. The powers above 50000 watts in “Zone I” are grandfathered with their pre 1962 authorized facilities or modified equivalent facilities. Outside Zone I, in Zone II, stations can be 100000 watts, That is above 43.5 degrees latitude in Michigan and parts of Illinois and Wisconsin, West to 90 degrees longitude.
Last edited by Ben Zonia on Tue Apr 25, 2023 7:44 pm, edited 1 time in total.
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Re: FM power in different areas
Power Answers
Most chicago FM transmitting is done from a few buildings a thousand ft tall or more, The FCC has a chart that shows required power Reduction when the antenna is over 500 ft tall for Class B and C stations. This is to Give an equivalent signal level at a certain distance from the transmitter, for 50 Kw and a 500 ft high antenna.
The stations, antennas around Detroit are often at 500 ft or less and can transmit the full 50 kw.
A few stations came on air before the later restrictions and grandfathered over 50 kW. Seems like the super power
WJFM in Grand Rapids had 470 kW for a long time, but when they moved the transmitter they were hit with the 100 kW restriction (in that area, over line "C") for ERP !
I remember when I worked at WXYZ, the FM (later WRIF) was up 800 ft on the TV tower and was limited to 27.5 kW!
Most chicago FM transmitting is done from a few buildings a thousand ft tall or more, The FCC has a chart that shows required power Reduction when the antenna is over 500 ft tall for Class B and C stations. This is to Give an equivalent signal level at a certain distance from the transmitter, for 50 Kw and a 500 ft high antenna.
The stations, antennas around Detroit are often at 500 ft or less and can transmit the full 50 kw.
A few stations came on air before the later restrictions and grandfathered over 50 kW. Seems like the super power
WJFM in Grand Rapids had 470 kW for a long time, but when they moved the transmitter they were hit with the 100 kW restriction (in that area, over line "C") for ERP !
I remember when I worked at WXYZ, the FM (later WRIF) was up 800 ft on the TV tower and was limited to 27.5 kW!
Re: FM power in different areas
I started typing my answer and had to feed a hungry, noisy cat, came back and found some one beat me (the ever watchful Ben Z.) with a similar answer
Yes Zone I and II, line C,
Yes Zone I and II, line C,
- ZenithCKLW
- Posts: 849
- Joined: Sat Nov 13, 2004 11:21 am
- Location: Livonia, MI
Re: FM power in different areas
Are there advantages or disadvantages between height and lower power vs. lower height and higher power?
-
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Re: FM power in different areas
I would think you would want to be higher up. Less interference from buildings, hills, etc.
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Re: FM power in different areas
I've also noticed that Chicago only has one grandfathered power FM, 90.1 WMBI (which also happens to be one of two stations below 92 MHz that cover most of the market). In Los Angeles and San Francisco, most of the full-market FMs have grandfathered power (with a few exceptions in each market)
Re: FM power in different areas
New York and Chicago both have FM signals with reduced ERP's due to the building heights many of the FM signals transmit from. In New York they are usually around 6,000 watts. In Toronto there are Class C1 stations on the CN tower that are 40,000 watts. One thing that is different about New York is that the main FM master antenna is in a central location. In many other cities this did not happen.
Re: FM power in different areas
Chicago is also the most densely populated city in the US. They can get more ears per Watt...
They are tucked right in with a few adjacent smaller markets.
They are tucked right in with a few adjacent smaller markets.
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Posting Content © 2024 TC Talks Holdings LP.
Re: FM power in different areas
Here are the Zones on a Map. I forgot the exact definitions, but this is more clear.
https://transition.fcc.gov/oet/info/map ... mzones.pdf
WFMT 98.7 in Chicago is also a grandfathered super power station at its height, significantly more powerful than the others would be at its 1542 feet HAAT, 6 kW vs 4.3 kW, as is WRIF 101.1 Detroit at 27 kW vs. 16 kW at 880 feet above average terrain. There are others, but these are the best examples now.
Here is the FCC program which computes the maximum ERP allowable under current rules at each HAAT for each Class of station and state or territory.
https://www.fcc.gov/media/radio/fmpower
https://transition.fcc.gov/oet/info/map ... mzones.pdf
WFMT 98.7 in Chicago is also a grandfathered super power station at its height, significantly more powerful than the others would be at its 1542 feet HAAT, 6 kW vs 4.3 kW, as is WRIF 101.1 Detroit at 27 kW vs. 16 kW at 880 feet above average terrain. There are others, but these are the best examples now.
Here is the FCC program which computes the maximum ERP allowable under current rules at each HAAT for each Class of station and state or territory.
https://www.fcc.gov/media/radio/fmpower
"I had a job for a while as an announcer at WWV but I finally quit, because I couldn't stand the hours."
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Re: FM power in different areas
WFMT and most of the many other FM stations on Sears Tower (and FM stations located in other metro city centers) use relativey low gain transmit antennas. Doing so produces higher relative ERP toward the elevation angles serving the typical region of high-rise buildings and listeners that are/may be present closer to the transmit antenna site.Ben Zonia wrote: ↑Tue Apr 25, 2023 7:50 pm... WFMT 98.7 in Chicago is also a grandfathered super power station at its height, significantly more powerful than the others would be at its 1542 feet HAAT, 6 kW vs 4.3 kW, as is WRIF 101.1 Detroit at 27 kW vs. 16 kW at 880 feet above average terrain. There are others, but these are the best examples now. ...
The graphic below shows an example illustrating this, although not specifically for WFMT.
WFMT and other Sears FM stations use their own single-bay antennas, stacked vertically on one of the two tallest masts atop the building.
- MWmetalhead
- Site Admin
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Re: FM power in different areas
I'm pretty sure WJFM's tower was always located near Patterson Rd. and 129th Ave. (aka Chief Noonday Rd.) in Yankee Springs Twp. just barely on the Barry County side of the Allegan - Barry border.Seems like the super power
WJFM in Grand Rapids had 470 kW for a long time, but when they moved the transmitter they were hit with the 100 kW restriction (in that area, over line "C") for ERP !
The power decrease to 320 kW ERP was requested by the owner, not mandated by the FCC.
Morgan Wallen is a piece of garbage.
Re: FM power in different areas
Originally, on 93.7, they were 115 kW.
They then went to 500 kW Horizontal only with a 12 Bay RCA BFA (H only) antenna.
At some point around 1970, they reduced to 470 kW H and 64 kW V and added V only Bays, and the TPO they could do with their dual combined modified VHF Low TV transmitters, 25 kW each.
WJFM went to 320 kW Circular Polarized around 1980 from 470 kW H 64 kW V because to be 470 kW Circular would require more TPO, a ridiculuously high TPO, so they went with basically the TPO they had and went 320 kW Circular.
They then went to 500 kW Horizontal only with a 12 Bay RCA BFA (H only) antenna.
At some point around 1970, they reduced to 470 kW H and 64 kW V and added V only Bays, and the TPO they could do with their dual combined modified VHF Low TV transmitters, 25 kW each.
WJFM went to 320 kW Circular Polarized around 1980 from 470 kW H 64 kW V because to be 470 kW Circular would require more TPO, a ridiculuously high TPO, so they went with basically the TPO they had and went 320 kW Circular.
"I had a job for a while as an announcer at WWV but I finally quit, because I couldn't stand the hours."
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Re: FM power in different areas
Looks like it was 115 kW from 24th and AB near Plainwell, MI around 420 feet HAAT before 1961. It was WJEF-FM until 1963.
https://licensing.fcc.gov/cgi-bin/prod/ ... r_id=81577
https://licensing.fcc.gov/cgi-bin/prod/ ... r_id=81577
"I had a job for a while as an announcer at WWV but I finally quit, because I couldn't stand the hours."
-Author Unknown
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Re: FM power in different areas
It looks like the former tower for WJEF-FM is now the location of WMUK 102.1. From that location at 420 feet HAAT, even with 115 kW, it wouldn't put a 70 dBu contour over Grand Rapids, only 60 dBu using the older F(50,50) curves and the Grand Rapids City Limits at the time, which were much smaller, and didn't go as far North. The 70 dBu F(50,50) COL requirement began in the early 1960s, though 93.7 may have begun as a Kalamazoo station.
This was also the location of the WKZO-TV tower in 1952, beginning as just 8 kW ERP, but in 1953 it was 81 kW ERP. They moved to the Yankee Springs Gun Lake location in 1960, with 100 kW ERP.
This was also the location of the WKZO-TV tower in 1952, beginning as just 8 kW ERP, but in 1953 it was 81 kW ERP. They moved to the Yankee Springs Gun Lake location in 1960, with 100 kW ERP.
"I had a job for a while as an announcer at WWV but I finally quit, because I couldn't stand the hours."
-Author Unknown
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