In addition to groundwave propagation, another factor would be whether a frequency is a clear channel frequency under the (old) international agreement.  Some frequencies such as 740 KHz, (CFZM Toronto) have stations licensed as "clear channel" operations.  If you are familiar with the CBC Milton (Hornby) transmitter site the facility is a single-tower, non-directional antenna. (CJBC 860 is also diplexed into that single tower)  CFZM/CJBC do not have multiple towers which if I can use the vernacular "shape" the signal in a particular direction to protect stations elsewhere on the same frequency.  Bottom line, non-directional operations would have better coverage - at the same power as highly directional stations which have to protect other stations on the same frequency in other directions.  CFRB protects WINS 1010 New York City, among other stations.   CFRB has different daytime and night time patters, which also impacts night time skywave radiation.  I hope this is useful. I'm old enough to remember when CFRB had a "manually operated" pattern change.  I worked the board in master control way back when and recall pressing the "pattern change" button.  I believe pattern change at 'RB has been automated for decades.

Last edited by tvguy (November 18, 2025 7:21 pm)

I am well aware of priority clear channels like 740/860 and shared clear channels like 1010/1050 which require different night patterns for protection purposes. I think the first answer summed things up quite succinctly.

mace wrote:

WWKB has a horrible night signal in the GTA. It always sounds distorted. Someone told me that we are getting a mix of the daytime ground wave and nighttime skywave signal which causes the distortion. True?

I was always sorry about how bad the reception for the former WKBW-AM was here. They were a pioneering Top 40 station with great personalities like Joey Reynolds and Sandy Beach and terrific branding from P.D. Jeff Kaye - and very few of us in Toronto could get it well enough to listen to it. 

It was a truly legendary station back in its day, close to the Southern Ontario border. And yet its signal was aimed the other way and those of us in Toronto could barely hear it clearly. What a shame.
  

That wasn't exactly a real KB chart. It was from the local Buffalo edition of GO Magazine, which was a national paper that was sponsored and given away free by one station in every market. In Buffalo, it was WKBW. In Toronto, it was CHUM. 

Most of the pages were filled with the exact same contemporary music news, while one was given over to the local station to promote themselves. It was given away for free at newsstands and record stores. 

Here's a sample from CHUM in July 1967. 

mace wrote:

WWKB has a horrible night signal in the GTA. It always sounds distorted. Someone told me that we are getting a mix of the daytime ground wave and nighttime skywave signal which causes the distortion. True?

My wife's family would visit relatives in the Gaspé Peninsula sixty odd years ago, and the kids would listen to WKBW in the evenings.

Thirty five years later, I was in Virginia Beach for a wedding, and decided to drive over to see the Norfolk Tides AAA baseball team play.  On the way there, I tuned in 1520 (by now known as WWKB), and heard the play by play of a Buffalo Bisons game.

And there was plenty of evening paid programming buying time on KB in the 90s and 00s, thanks to that nighttime signal pattern.

From what I understand. KB sends their entire night signal eastward to protect KOKC [the former KOMA] in Oklahoma City.  In its top 40 days it had plenty of listeners in the Eastern Canadian provinces and American states.

Doesn't look like the pattern has changed much over the years. There is a null towards Toronto, which I suspect was to protect CHIN 1540.

I suspect they had to protect the now defunct, adjacent 1510 CKOT from Tillsonburg.

mace wrote:

Evuguy wrote:

I suspect they had to protect the now defunct, adjacent 1510 CKOT from Tillsonburg.

Good point. I hadn't thought of that. I wonder why that is still required even though CKOTvacated 1510 years ago. In the CFOS thread, I think someone mentioned that the 560 in Munroe. Mi still has to protect the Owen Sound station even though they are now FM only.

Correct. The protections remain for now defunct stations. Even if the protections were eliminated and opportunities were available to expand coverage the cost to modify directional antenna arrays would be quite expensive. It is unlikely most stations would spend the money to do so.
 

Actually WKBW moved to 1520 in 1941. CKOT didn't start until 1955, so they weren't actually protected, but did take advantage of the reduced signal in their direction.
It's not unusual for stations sharing clear channels to use the same pattern day and night. The market for WKBW was clearly Buffalo/Niagara and east. Shooting extra signal out over Lake Erie with an omni signal daytime would have been a waste, as well as reducing the signal strength in Buffalo. Being at the high end of the dial, the groundwave signal deterioirates rapidly.