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December 8, 2020 6:30 pm  #1


Why More & More AM Antenna Sites Are Up For Sale

The air space is being replaced by the real space. In many cases, the land those powerful 50K AM transmitters sit on is worth more in real estate than the stations themselves. And many are being sold to be repurposed. 

AM Radio Transmitter Sites Now Valuable Real Estate

 

December 8, 2020 6:37 pm  #2


Re: Why More & More AM Antenna Sites Are Up For Sale

On SOWNY, I don't expect this thread to be ........ er...... well received
 


Cheers,
Jody Thornton
 
 

December 8, 2020 6:45 pm  #3


Re: Why More & More AM Antenna Sites Are Up For Sale

Yes, I agree Jody...the message transmitted here could cause some static, even interference with some readers..https://cdn.boardhost.com/emoticons3/w00t.png

 

December 8, 2020 7:13 pm  #4


Re: Why More & More AM Antenna Sites Are Up For Sale

So...two AM transmitters walk into a bar...they are surprised to see that the bar keep is former Prime Minister Joe Clark. " Hey fella's" says Joe..."could I ask you a question before you order?"  "Ok" says the 50K transmitter.  Clark asks, "what is the totality of your acreage?"  The one transmitter shakes his antenna and mutters to his friend... "Oh good lord, he thinks we're farmers.. I can now see why a lot of people thought that Clark's bandwidth was kind of lacking..."  https://cdn.boardhost.com/emoticons3/cwy.png
    

 

December 8, 2020 7:43 pm  #5


Re: Why More & More AM Antenna Sites Are Up For Sale

Well paterson1, I know you'll get some flack for that joke, so maybe if I try to get back on topic, it will QUAM the waters for you,

It's a good thing I was decisive in this matter - I mean there are possibly four ways this could go 
(see what I did there?)
 


Cheers,
Jody Thornton
 
 

December 8, 2020 7:52 pm  #6


Re: Why More & More AM Antenna Sites Are Up For Sale

the amplitude of this thread is quite radiating

 

December 8, 2020 10:14 pm  #7


Re: Why More & More AM Antenna Sites Are Up For Sale

Just out of curiosity, could someone explain to me the technical reason why AM stations do not (cannot?) transmit from locations that FM stations use such as the top of the CN Tower or First Canadian Place in Toronto or other skyscrapers. Is it because they are too high, powerful 50 kW+ AM transmitters are too large to be accommodated on top of a building, or because if you place an AM transmitter in the central business district there's too much interference from other high buildings etc?

 

December 8, 2020 10:23 pm  #8


Re: Why More & More AM Antenna Sites Are Up For Sale

Hansa wrote:

Just out of curiosity, could someone explain to me the technical reason why AM stations do not (cannot?) transmit from locations that FM stations use such as the top of the CN Tower or First Canadian Place in Toronto or other skyscrapers. Is it because they are too high, powerful 50 kW+ AM transmitters are too large to be accommodated on top of a building, or because if you place an AM transmitter in the central business district there's too much interference from other high buildings etc?

There are members here that can explain it way better than me, but it's the difference between ground-wave and line-of-sight signal propagation.

Different bands of frequencies require different techniques. FM needs the height, AM does not.

https://www.rfwireless-world.com/Terminology/sky-wave-vs-LOS-wave-vs-ground-wave.html


 


 
 

December 9, 2020 12:01 am  #9


Re: Why More & More AM Antenna Sites Are Up For Sale

Hansa wrote:

Just out of curiosity, could someone explain to me the technical reason why AM stations do not (cannot?) transmit from locations that FM stations use such as the top of the CN Tower or First Canadian Place in Toronto or other skyscrapers. Is it because they are too high, powerful 50 kW+ AM transmitters are too large to be accommodated on top of a building, or because if you place an AM transmitter in the central business district there's too much interference from other high buildings etc?

It has to do with the frequency the station operates on.  The lower the frequency, the larger the antenna.

In radio broadcasting, we all tend to refer to the modulation type (AM or FM), when we are really referring to the frequency.

Broadcast stations that use AM (amplitude modulation) operate on fairly low frequencies (like 1010kHz) and therefore need a large antenna (hundreds of feet in length). Typically, a tall tower is used as the antenna.  Some stations are omni-directional can use a single tower antenna (such as Toronto's 740).  "AM" stations that must send their signal in a specific direction use multiple antennas (towers) in order to create the required pattern.  These towers must often be spaced hundreds of feet apart.  This can result in a very large chunk of land required to support these directional antennas (such as Toronto's 1050, 680 or 640).  Also, these lower frequencies require a "good ground" as they tend to travel long distances along the ground.

Broadcast stations that use FM (frequency modulation) operate on relatively high frequencies (such as 94.1MHz or 100.7MHz) and their antennas are much shorter (about 3 feet).  These higher frequencies tend to be line-of-site and therefore, the higher, the better.  In this case, a tall tower is typically used to support the antenna.  "FM" stations can also be directional, which is achieved by using multiple antennas on the same mast.

The CN Tower is a support structure for the (relatively) small "FM" antennas.  It cannot be used to support the larger low frequency ("AM") antennas.


Of note:

- The amount of power a station broadcasts with is not a factor in antenna size

- Technically speaking, frequency modulation could be used on the "AM" broadcast band or conversely, amplitude modulation could be used on the "FM" broadcast band

- Commercial aircraft use AM modulation on frequencies slightly above the "FM" broadcast band

- The little hand held two-way radios you can buy at Costco or WalMart use FM modulation

- CFTR, CHIN, CFGM (now CFMJ) all had large antenna systems in Mississauga years ago.  Now all housing

 

 

December 9, 2020 11:59 am  #10


Re: Why More & More AM Antenna Sites Are Up For Sale

In Phase wrote:

Hansa wrote:

Just out of curiosity, could someone explain to me the technical reason why AM stations do not (cannot?) transmit from locations that FM stations use such as the top of the CN Tower or First Canadian Place in Toronto or other skyscrapers. Is it because they are too high, powerful 50 kW+ AM transmitters are too large to be accommodated on top of a building, or because if you place an AM transmitter in the central business district there's too much interference from other high buildings etc?

It has to do with the frequency the station operates on.  The lower the frequency, the larger the antenna.

In radio broadcasting, we all tend to refer to the modulation type (AM or FM), when we are really referring to the frequency.

Broadcast stations that use AM (amplitude modulation) operate on fairly low frequencies (like 1010kHz) and therefore need a large antenna (hundreds of feet in length). Typically, a tall tower is used as the antenna.  Some stations are omni-directional can use a single tower antenna (such as Toronto's 740).  "AM" stations that must send their signal in a specific direction use multiple antennas (towers) in order to create the required pattern.  These towers must often be spaced hundreds of feet apart.  This can result in a very large chunk of land required to support these directional antennas (such as Toronto's 1050, 680 or 640).  Also, these lower frequencies require a "good ground" as they tend to travel long distances along the ground.

Broadcast stations that use FM (frequency modulation) operate on relatively high frequencies (such as 94.1MHz or 100.7MHz) and their antennas are much shorter (about 3 feet).  These higher frequencies tend to be line-of-site and therefore, the higher, the better.  In this case, a tall tower is typically used to support the antenna.  "FM" stations can also be directional, which is achieved by using multiple antennas on the same mast.

The CN Tower is a support structure for the (relatively) small "FM" antennas.  It cannot be used to support the larger low frequency ("AM") antennas.


Of note:

- The amount of power a station broadcasts with is not a factor in antenna size

- Technically speaking, frequency modulation could be used on the "AM" broadcast band or conversely, amplitude modulation could be used on the "FM" broadcast band

- Commercial aircraft use AM modulation on frequencies slightly above the "FM" broadcast band

- The little hand held two-way radios you can buy at Costco or WalMart use FM modulation

- CFTR, CHIN, CFGM (now CFMJ) all had large antenna systems in Mississauga years ago.  Now all housing

 

Very good info.  Question on this, some independent stations back in the day especially 50k watts and up had several bays.  I remember CHAY in Barrie before they had a master fm system installed on the VR Tower was 100,000 watts omni and a 10 bay system.   The lower the power the less bays.   How come?

 

December 9, 2020 12:17 pm  #11


Re: Why More & More AM Antenna Sites Are Up For Sale

Very good info.  Question on this, some independent stations back in the day especially 50k watts and up had several bays.  I remember CHAY in Barrie before they had a master fm system installed on the VR Tower was 100,000 watts omni and a 10 bay system.   The lower the power the less bays.   How come?

The less the power, the less metal you need in the air - AM or FM. That being said, you can pump low power into an antenna capable of high power. But not the other way around.
AM - those CBC 40 repeaters only use a long wire between two polls about 100' feet up. They are not capable of much more. Those 1000w AM stations in Mississauga such just use one short poll. A 50kW station would need a big tower [for omni-directional] or several towers [for directional]
FM - you see those big arrays as noted above. CJMB in Peterborough at 175w just has a small two bay antenna.

 

 

December 9, 2020 12:22 pm  #12


Re: Why More & More AM Antenna Sites Are Up For Sale

markow202 wrote:

Very good info.  Question on this, some independent stations back in the day especially 50k watts and up had several bays.  I remember CHAY in Barrie before they had a master fm system installed on the VR Tower was 100,000 watts omni and a 10 bay system.   The lower the power the less bays.   How come?

The number of bays isn't directly related to the power of the station. 

More antenna bays allow you to generate a higher ERP (effective radiated power) with a lower TPO (transmitter power out) - in effect, an antenna with more bays has what's called "higher gain."

You can't get something for nothing, of course - the higher the antenna gain and the more bays in use, the more concentrated the horizontal pattern of the antenna becomes. 

It's an overgeneralization, but think of a one-bay antenna as a perfect spherical radiator: the energy produced by the transmitter is dispersed in a perfect sphere around the antenna. Doesn't matter if you're directly below the antenna, or in a plane flying straight above it, or out at the horizon, you get the same amount of RF directed at you.

Start adding bays and that sphere turns into an ever-flatter donut as more of the energy is dispersed straight out and less is dispersed straight down or straight up.

There's rarely a need for an FM station to radiate upwards, of course; the need to radiate downward or at shallow angles depends heavily on where your population is in relation to the tower. The VR tower is out in a relatively thinly populated area, as I recall, with more of the desired population for CHAY at some distance. So using multiple bays works in two ways: first, it still directs the 93.1 signal where the population is, and second, it allows the use of a relatively low-powered transmitter to combine with antenna gain to produce a 100 kW ERP signal. I'd guess the CHAY transmitter is probably somewhere in the 20 kW range, which is cheaper on the hydro bill than it would be to run 100 kW of transmitter into a single-bay antenna. (Which nobody ever does - the highest power generally available for an FM transmitter is 40 kW, so you always have multiple-bay, higher-gain antennas for FM stations of 50 kW or more.) 

Using multiple-bay antennas is also a must sometimes when you have to reduce downward radiation to meet RF radiation standards when you have occupied buildings in close proximity to the FM site. 

Hope that helps!
 

 

December 9, 2020 12:55 pm  #13


Re: Why More & More AM Antenna Sites Are Up For Sale

I often wonder what the WLW (700) tower in Cincinnati looked like back at the time it was 500,000 watts. And no, that's not a misprint. It was for a time the strongest signal on the planet and it probably came in on your toothbrush. Eventually it went back to the more standard 50K signal and it's still a powerful clear channel station that can be heard across much of the eastern seaboard.

I once imagined the engineers approaching the thing in a hazmat suit or radiation-proof underwear! Incredible to think of a station operating at that power. 

WLW's superpower days

This snippet is from the 1930 or 40s, when CFRB was on 690. 

https://i.ibb.co/fnWN19T/CFRB-WLW-Signal-Oct-1950.jpg

https://upload.wikimedia.org/wikipedia/commons/e/e5/WLW-AM_RadioTower.PNG

     Thread Starter
 

December 9, 2020 1:20 pm  #14


Re: Why More & More AM Antenna Sites Are Up For Sale

markow202 wrote:

  Very good info.  Question on this, some independent stations back in the day especially 50k watts and up had several bays.  I remember CHAY in Barrie before they had a master fm system installed on the VR Tower was 100,000 watts omni and a 10 bay system.   The lower the power the less bays.   How come?

To your point markow202, almost all "FM" stations have more than one "bay" in their antenna system. A "bay" can be considered as a single antenna and is the most basic form of antenna.  If you mounted a single "bay" on the side of a tower, it would provide a somewhat directional pattern (favouring the direction of the antenna) since the tower can act as a barrier to the signal.  Multiple bays (usually 3 or 4) are typically installed around a tower to provide an omni-directional pattern.  You can also add "bays" vertically on a tower.  As you add "bays" vertically, it will increase the overall signal strength (typically called "gain").  It is very common to see "FM" antennas with 6-12 "bays" on a tower.
 
To determine the maximum "effective" power (ERP) of a station, you multiply the actual transmitter power by the "gain" of the antenna.  If for example, your transmitter was 5kW and your multi-bay antenna had a "gain" of 10, your ERP would be 50kW (5kW X 10).  Note that you can have similar ERP's for an omni-directional station and a directional station.  The difference is that the "ERP" is the same in all directions for the omni station whereas the "ERP" is in a specific direction for the directional station.
 
The "newish" CHAY antenna in Barrie is very unique and very cool (I think).  As you note, it carries multiple FM stations.  What is unique is that supports the omni-directional CHAY along with the directional CIQB and directional CFJB.  It is challenging to configure a common antenna system to accommodate both omni-directional AND independently directional stations.  CHAY uses all antenna bays, while CIQB and CFJB use specifically selected antenna bays.  Each station has its own ERP.
 
It's complicated but I hope this provides some insight into how these stations operate.

 

 

December 9, 2020 1:45 pm  #15


Re: Why More & More AM Antenna Sites Are Up For Sale

In Phase wrote:

markow202 wrote:

  Very good info.  Question on this, some independent stations back in the day especially 50k watts and up had several bays.  I remember CHAY in Barrie before they had a master fm system installed on the VR Tower was 100,000 watts omni and a 10 bay system.   The lower the power the less bays.   How come?

To your point markow202, almost all "FM" stations have more than one "bay" in their antenna system. A "bay" can be considered as a single antenna and is the most basic form of antenna.  If you mounted a single "bay" on the side of a tower, it would provide a somewhat directional pattern (favouring the direction of the antenna) since the tower can act as a barrier to the signal.  Multiple bays (usually 3 or 4) are typically installed around a tower to provide an omni-directional pattern.  You can also add "bays" vertically on a tower.  As you add "bays" vertically, it will increase the overall signal strength (typically called "gain").  It is very common to see "FM" antennas with 6-12 "bays" on a tower.
 
To determine the maximum "effective" power (ERP) of a station, you multiply the actual transmitter power by the "gain" of the antenna.  If for example, your transmitter was 5kW and your multi-bay antenna had a "gain" of 10, your ERP would be 50kW (5kW X 10).  Note that you can have similar ERP's for an omni-directional station and a directional station.  The difference is that the "ERP" is the same in all directions for the omni station whereas the "ERP" is in a specific direction for the directional station.
 
The "newish" CHAY antenna in Barrie is very unique and very cool (I think).  As you note, it carries multiple FM stations.  What is unique is that supports the omni-directional CHAY along with the directional CIQB and directional CFJB.  It is challenging to configure a common antenna system to accommodate both omni-directional AND independently directional stations.  CHAY uses all antenna bays, while CIQB and CFJB use specifically selected antenna bays.  Each station has its own ERP.
 
It's complicated but I hope this provides some insight into how these stations operate.

 

Thanks for the info guys!  Easy to understand now.  I also remember looking at Jewel 88.5 site where it is more directional to the north and it has I believe 3 bays atop.  One pointing southwest and two pointing north.  Makes sense.

Im guessing the CN Tower one inside the radome is similar to the CKVR master fm...and goes all around the mast inside since they are all omni directional stations.  The CN site also I read had to be specially designed as the nulls that had to be filled (population directly below) 

Last edited by markow202 (December 9, 2020 2:04 pm)

 

December 11, 2020 12:27 pm  #16


Re: Why More & More AM Antenna Sites Are Up For Sale

Another reason AM transmitter sites require so much room: generally there are about 120 'ground radials' wires buried a few inches below the surface of the ground. These radials come out from the tower base like spokes on a wagon wheel and can be hundreds of feet in length depending on the tower height and frequency of the station. Directional stations use multiple towers to aim their signal thus requiring additional space. For me a directional AM array is a tribute to engineering and a sight to behold.