Acceptable registrations in the queue through March 16 at 11:00a ET have now been activated. Enjoy! -M.W.

Terms of Use have been amended effective October 6, 2019. Make sure you are aware of the new rules! Please visit this thread for details: https://www.mibuzzboard.com/phpBB3/view ... 16&t=48619

FM power in different areas

The technical side of broadcasting. Think IBOC is a sham? Talk about it here! How about HDTV? Post DX reports here as well.
User avatar
ZenithCKLW
Posts: 833
Joined: Sat Nov 13, 2004 11:21 am
Location: Livonia, MI

FM power in different areas

Post by ZenithCKLW » Tue Apr 25, 2023 4:25 pm

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?



User avatar
Ben Zonia
Posts: 2143
Joined: Sat Jun 03, 2006 10:35 pm
Location: Honor

Re: FM power in different areas

Post by Ben Zonia » Tue Apr 25, 2023 5:21 pm

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.


"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

k8jd
Posts: 603
Joined: Fri Jun 28, 2013 3:35 pm
Location: Commerce, MI

Re: FM power in different areas

Post by k8jd » Tue Apr 25, 2023 5:23 pm

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!



k8jd
Posts: 603
Joined: Fri Jun 28, 2013 3:35 pm
Location: Commerce, MI

Re: FM power in different areas

Post by k8jd » Tue Apr 25, 2023 5:25 pm

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 :D
Yes Zone I and II, line C,



User avatar
ZenithCKLW
Posts: 833
Joined: Sat Nov 13, 2004 11:21 am
Location: Livonia, MI

Re: FM power in different areas

Post by ZenithCKLW » Tue Apr 25, 2023 6:33 pm

Are there advantages or disadvantages between height and lower power vs. lower height and higher power?



Mega Hertz
Posts: 4265
Joined: Fri Jun 15, 2012 10:09 pm
Location: Brighton

Re: FM power in different areas

Post by Mega Hertz » Tue Apr 25, 2023 6:36 pm

I would think you would want to be higher up. Less interference from buildings, hills, etc.


"Internet is no more like radio than intravenous feeding is like fine dining."
-TurkeyTop

ftballfan
Posts: 875
Joined: Thu Sep 17, 2009 6:38 pm

Re: FM power in different areas

Post by ftballfan » Tue Apr 25, 2023 6:50 pm

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)



Marcus
Posts: 340
Joined: Fri Jan 21, 2005 1:08 pm
Location: Sarnia, Ontario

Re: FM power in different areas

Post by Marcus » Tue Apr 25, 2023 7:12 pm

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.



User avatar
TC Talks
Posts: 10106
Joined: Wed Oct 26, 2005 2:41 am

Re: FM power in different areas

Post by TC Talks » Tue Apr 25, 2023 7:42 pm

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.


“The more you can increase fear of drugs, crime, welfare mothers, immigrants and aliens, the more you control all of the people.”
― Noam Chomsky

Posting Content © 2024 TC Talks Holdings LP.

User avatar
Ben Zonia
Posts: 2143
Joined: Sat Jun 03, 2006 10:35 pm
Location: Honor

Re: FM power in different areas

Post by Ben Zonia » Tue Apr 25, 2023 7:50 pm

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


"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

Rich F.
Posts: 80
Joined: Wed May 29, 2019 5:53 am
Location: Illinois USA
Contact:

Re: FM power in different areas

Post by Rich F. » Sat Apr 29, 2023 12:07 pm

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. ...
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.

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.

Image



User avatar
MWmetalhead
Site Admin
Posts: 11875
Joined: Sun Oct 31, 2004 11:23 am

Re: FM power in different areas

Post by MWmetalhead » Sat Apr 29, 2023 12:10 pm

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'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.

The power decrease to 320 kW ERP was requested by the owner, not mandated by the FCC.



User avatar
Ben Zonia
Posts: 2143
Joined: Sat Jun 03, 2006 10:35 pm
Location: Honor

Re: FM power in different areas

Post by Ben Zonia » Sat Apr 29, 2023 6:59 pm

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.


"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

User avatar
Ben Zonia
Posts: 2143
Joined: Sat Jun 03, 2006 10:35 pm
Location: Honor

Re: FM power in different areas

Post by Ben Zonia » Sat Apr 29, 2023 8:44 pm

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


"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

User avatar
Ben Zonia
Posts: 2143
Joined: Sat Jun 03, 2006 10:35 pm
Location: Honor

Re: FM power in different areas

Post by Ben Zonia » Sun Apr 30, 2023 9:15 am

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.


"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

Post Reply Previous topicNext topic