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FM power in different areas

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Plate Cap
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Re: FM power in different areas

Post by Plate Cap » Sun Apr 30, 2023 10:58 am

ZenithCKLW wrote:
Tue Apr 25, 2023 6:33 pm
Are there advantages or disadvantages between height and lower power vs. lower height and higher power?
Height trumps power virtually every time.

By having more antenna height, you create a larger area of line of sight, and that is, for the most part, what determines coverage. Free space path attenuation (the resultant decrease in signal strength as an RF signal passes through air) is increased by distance, but is almost negligible at broadcast FM frequencies compared to the shadowing from objects on the ground that prevent line of sight.

Other than the pure ability to SEE your intended reception area from the perspective of an antenna on a tower, one can theoretically examine the height vs. power question very easily by imagining your having an extremely powerful "flashlight" with you on the tower. You could play the beam all over the place, and up to the edge of the curvature of the earth, and you would be able to shine your theoretic infinitely powerful flashlight on anything that your elevation allowed you to look over obstructions and see. Those are the areas your radio signal would be received at. However, turning up the power on your flashlight would not allow you drill through mountains, hills, buildings, or other obstructions and light up new areas. Only height can make that happen.

Back to reality, more power gives you less whip flutter as you are driving around such obstructions, will tend to fill 'dead' areas with reflections from other obstructions (and maybe cause new problems doing so), and gives you better close-in building penetration to table radios, portable radios, and the like. But, the advantage is often not worth the power bill.

The 50kw/500' standard was put into place when the FCC thought and ruled like engineers, and not like today where they instead often choose to serve special interests and political ideals. It is a pretty good balance of height and power.

It would be a blast to own a grandfathered 'flamethrower' like WJMZ with 100kW at 1000', or even closer to home, WOMC, but in reality, you just don't talk much further than the horizon line from your antenna location, and a whole lot of power just raises your power bill and your FCC consultant's income sometimes without any real advantage.


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Ben Zonia
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Re: FM power in different areas

Post by Ben Zonia » Sun Apr 30, 2023 2:28 pm

Unless terrain is almost completely flat (large water bodies with waves might be one possibility, but there are also the refractive atmospheric effects) around any stream or larger body of water, the terrain on either side is higher, and shadows the near shoreline, and favors the far shoreline. This can affect even high HAAT, particularly with the proliferation of new Class As dating back to Docket 80-90. However, even 320 kW from 780 feet at 30 miles has noticeable shadowing near the Grand River in Grand Rapids.

Signal intensity from lower ERP is a consideration. The late great Harold Munn said that 400 feet HAAT was the maximum he recommended for a Class A. However, there are a number of 250 watt translators at such high HAAT, circa 1000 feet, that are about the FCC "FM Power" equivalent of a 2000 watt Class A, typical of a an old 3000 watt Class A on an AM tower or low height tower in FAA restricted areas. But those reportedly seem to not penetrate houses that well.


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Ben Zonia
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Re: FM power in different areas

Post by Ben Zonia » Sun Apr 30, 2023 2:45 pm

For the FCC FM Power calculation, this link will be reposted on this page of the thread.

https://www.fcc.gov/media/radio/fmpower


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Marcus
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Re: FM power in different areas

Post by Marcus » Sun Apr 30, 2023 3:06 pm

I'm keeping an eye on 95.3 FM in Hamilton, ON as the tower they are currently on will be removed for suburban development.
Both of the TV stations will transmit from near Rock Chapel to the northwest and will increase ERP. They will also be 63 meters or 206' higher above sea level than they are right now. Unlike the TV stations, 95.3 FM is non directional.

The CRTC decision regarding CHCH and CITS TV are in the link below

https://applications.crtc.gc.ca/instanc ... #202201432



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Ben Zonia
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Re: FM power in different areas

Post by Ben Zonia » Sun Apr 30, 2023 3:47 pm

CKDS 95.3 was Beautiful Music in the 1970s as I recall, and would fade in and out in Harrisville, MI on a good Sony Portable. There were relatively few FM stations then.


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k8jd
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Re: FM power in different areas

Post by k8jd » Wed May 10, 2023 10:51 am

When I was a kid I had some books about broadcasting engineering, there were several charts showing signal strength for various distances VS antenna height and power, in the FM band. I converted the data to show how the signal strength varied with distance with low height and high power and viceversa,
I believe I proved a low antenna and high power faded more slowly as distance increased, compared to high tower with lower power. The later faded quickly over distance. This was more evident at the horizon in the fringe areas. The high power seemed to do better there even with a lower tower.



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Ben Zonia
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Re: FM power in different areas

Post by Ben Zonia » Wed May 10, 2023 11:14 am

k8jd wrote:
Wed May 10, 2023 10:51 am
When I was a kid I had some books about broadcasting engineering, there were several charts showing signal strength for various distances VS antenna height and power, in the FM band. I converted the data to show how the signal strength varied with distance with low height and high power and viceversa,
I believe I proved a low antenna and high power faded more slowly as distance increased, compared to high tower with lower power. The later faded quickly over distance. This was more evident at the horizon in the fringe areas. The high power seemed to do better there even with a lower tower.
Beyond the line of sight, the signal is received by tropospheric scattering, and ERP determines the strength of the signal. According to people who listen (some say it's still not officially allowed) to FM in airplanes, they'll tell you that the Sears/Willis Hancock/Whatever Chicago stations don't come in much at all, like WBBM-FM 96.3, and high ERP stations like WLXT 96.3 are heard above places like Muskegon, which is easily identifiable if you look out the window.


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Re: FM power in different areas

Post by Turkeytop » Wed May 10, 2023 1:39 pm

During the 1970s we were living up in one of the Northern Lake Huron counties in Ontario.

There was no local FM at all, only far fringe. All FM reception was DX. I had an outdoor Yagi antenna and would just search around for whatever might be available on any day. Sometimes from Michigan and sometimes from southern Ontario.

I was sometimes able to recieve signals from Toronto. That ended when they all migrated to the CN Tower and drastically reduced their power. Reception from Toronto became rare after that.


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Re: FM pIower in different areas

Post by Ben Zonia » Wed May 10, 2023 7:30 pm

Besides the CN tower being well above 1000 feet, 305 meters, the Canada also agreed with the US on creating Class C1, which also allowed and required stations to reduce power if they were on the tower, and Class Bs reduced even more to the 150 meter/~500 foot level.

When the band wasn't so crowded, the stations that weren't on the Sears/Willis or Hancock/Whatever were able to keep substantial power, such as WYCA 92.3, WYEN 106.7, and WGCI 107.5, still came in more frequently. WLS-TV on the Circle 7 Marina City tower with 316 kW was seen, until they moved to Sears/Willis, frequently in outstate Michigan. Nearby WTTW 11 with 316 kW came in better, if you were away from WTOL 11, and before WBKB 11 came on the air in Alpena, oddly enough, with the former call letters of WLS-TV 7.
Last edited by Ben Zonia on Wed May 10, 2023 8:30 pm, edited 1 time in total.


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ZenithCKLW
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Re: FM power in different areas

Post by ZenithCKLW » Wed May 10, 2023 7:56 pm

Was there a magic formula determining 316 kw to be ideal for VHF-HI TV stations? I remember analog WXYZ-TV was also 316 kw.



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Re: FM power in different areas

Post by Ben Zonia » Wed May 10, 2023 8:39 pm

Back when it was decided on, they took into account the increased shadowing and signal loss, plus the noise level/sensitivity of TVs at Channels 7-13, and decided on a 5 dB increase over Channels 2-6. Rich may have more insight on this. He once worked at WKNX-TV Channel 57, which at some point was 175 kW from the Treanor Street tower where WILZ 104.5 is now, so he is probably an expert on circuit noise.


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Re: FM power in different areas

Post by audiophile » Sun May 14, 2023 12:37 pm

Ben Zonia wrote:
Wed May 10, 2023 11:14 am
k8jd wrote:
Wed May 10, 2023 10:51 am
When I was a kid I had some books about broadcasting engineering, there were several charts showing signal strength for various distances VS antenna height and power, in the FM band. I converted the data to show how the signal strength varied with distance with low height and high power and viceversa,
I believe I proved a low antenna and high power faded more slowly as distance increased, compared to high tower with lower power. The later faded quickly over distance. This was more evident at the horizon in the fringe areas. The high power seemed to do better there even with a lower tower.
Beyond the line of sight, the signal is received by tropospheric scattering, and ERP determines the strength of the signal. According to people who listen (some say it's still not officially allowed) to FM in airplanes, they'll tell you that the Sears/Willis Hancock/Whatever Chicago stations don't come in much at all, like WBBM-FM 96.3, and high ERP stations like WLXT 96.3 are heard above places like Muskegon, which is easily identifiable if you look out the window.
WOMC absolutely screams in airplane reception over Tennessee and Kentucky.


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syntheticexctasy
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Re: FM power in different areas

Post by syntheticexctasy » Fri May 19, 2023 12:48 pm

Random info:

I just completed a trip to chicago and back via I94 from Wayne County. Slight tropospheric enhancement. Coming back I decided to fiddle with the dial a bit (headed east). For anyone interested here are my absolutely 100% scientific observations.

WKQX 101.1 - unlistenable by about MM 50 with nothing fighting it.
WFMT 98.7 (highest up on the willis tower) - unlistenable by about MM 100. Around MM 70-85, encountered some slight CCI from WFGR Grand Rapids.
WLIT 93.9 - unlistenable by about MM 80. would've been listenable further, but IBOC and splatter from WBCT won out.
WOJO 105.1 - unlistenable by about MM 80, nothing fighting it
WCHI 95.5 - unlistenable by about MM 55-60, w238cl portage winning out. pretty impressive signal for a pea shooter (the translator, that is)
WDRV 97.1 - unlistenable by about MM 70, nothing fighting it but a lot of splatter and iboc hash.

Didn't really monitor any others, but I should've been checking WMBI also.

Boy would it suck to live in this neighborhood (and have any interest at all in RF)

https://www.google.com/maps/place/41%C2 ... .007?hl=en



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Ben Zonia
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Re: FM power in different areas

Post by Ben Zonia » Fri May 19, 2023 3:38 pm

Where the lower ERP Chicago Area FM stations fizzle out is probably determined by two factors. One is terrain and earth curvature, where you fall into a shadow. The other is the milieu of signals now on cochannel and first adjacent channels that weren't there before Docket 80-90. In Southwest Michigan, there are quite a few of these, as many were dropped in as 3000 watt/100 meter HAAT facilities, and they only had to be 101 miles away cochannel, and 65 miles first adjacent channel, from the Chicago Area FMs.

The second and third adjacent channels had to be 43 miles away, but that was an increase from 40 miles. But across Lake Michigan, that wasn't a factor. Docket 80-90 INCREASED some distance separation requirements, despite what many believed, and so did the 6000 watt Class A rules. The NAB loved that, because it kept new stations from nearby markets from competing with them. Now they blot those stations out completely with translators in large cities, high on TV towers where they interfere with stations from neighboring markets, because the propagation model for interference didn't take those factors into account. Of course, now they need those nearby rimshots to simulcast their AM stations, after they tried to keep them out.


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syntheticexctasy
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Re: FM power in different areas

Post by syntheticexctasy » Fri May 19, 2023 4:09 pm

Ben Zonia wrote:
Fri May 19, 2023 3:38 pm
Where the lower ERP Chicago Area FM stations fizzle out is probably determined by two factors. One is terrain and earth curvature, where you fall into a shadow. The other is the milieu of signals now on cochannel and first adjacent channels that weren't there before Docket 80-90. In Southwest Michigan, there are quite a few of these, as many were dropped in as 3000 watt/100 meter HAAT facilities, and they only had to be 101 miles away cochannel, and 65 miles first adjacent channel, from the Chicago Area FMs.

The second and third adjacent channels had to be 43 miles away, but that was an increase from 40 miles. But across Lake Michigan, that wasn't a factor. Docket 80-90 INCREASED some distance separation requirements, despite what many believed, and so did the 6000 watt Class A rules. The NAB loved that, because it kept new stations from nearby markets from competing with them. Now they blot those stations out completely with translators in large cities, high on TV towers where they interfere with stations from neighboring markets, because the propagation model for interference didn't take those factors into account. Of course, now they need those nearby rimshots to simulcast their AM stations, after they tried to keep them out.
I think that on this drive specifically (I haven't looked) the elevation increases dramatically as you drive e/ne on I94. This probably also has some effect. Also the water path helps a bit - for instance, where I lost WFMT, nearly half of the path was over water. Can't post a screenshot I guess. Oh well, it's 130mi - about 75 miles past the "radio horizon".

I generally enjoy listening to WIIL on a trip to Chicago - I used to be able to hear it around MM 80 (I-94, Michigan) and all the way into the north side of Chicago, however a new translator in both Chicago and Michigan City make it a bit difficult anymore - and on this day in particular, there didn't seem to be much if any signal there for me to grab once I got east of Michigan City.

BTW the translator in Michigan City (95.1 W236BD) sounds completely terrible. MWMetalHead would have a fit!! It's a translator for WIMS AM. It sounds like they're taking the AM signal in on a tabletop radio, then compressing it digitally and spitting it out on a talking house transmitter - but with a lot more ERP.

I noticed that WWDV Zion, IL (96.9) is now simulcasting WDRV in Chicago (97.1). While I was scanning from the north end, I had to do a double take - hearing WDRV on 96.9 made me think twice LOL



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