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WBBM 780 to diplex with WSCR 670

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MWmetalhead
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WBBM 780 to diplex with WSCR 670

Post by MWmetalhead » Mon Nov 27, 2017 8:32 am

For those who haven't heard, about 45 days ago, WBBM 780 applied to decrease power to 35 kW days / 42 kW nights and diplex from the WSCR 670 site in Chicago's western suburbs.

The new site appears to be fewer than five miles further away from Grand Rapids.

A couple folks on the RadioDiscussions.com message board claim that because the WSCR tower site is taller, despite the drop in power, WBBM should not lose any meaningful groundwave coverage.

Personally, I'm skeptical. The engineering exhibits submitted to the FCC clearly show some minor contraction in the 0.5 mV/m contour.

Moreover, on most (not all) radios I've used over the years, the groundwave signal strength of WSCR and WBBM in western Michigan seems to be about the same. Perhaps on 1 or 2 radios, WSCR was a little stronger. WSCR's signal does carry farther eastward, but this is likely due in part to the fact WBBM encounters adjacent channel interference from WSGW.

I would be curious to get everyone's take on this topic, including the challenges of diplexing two mega-powered AM stations that are spaced only 110 kHz apart.

I also don't understand why WBBM's application includes protection vis-a-vis CKLW over American soil. I thought Canadian stations weren't afforded protection over U.S. soil? Are the rules different for AM than FM?
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Re: WBBM 780 to diplex with WSCR 670

Post by audiophile » Mon Nov 27, 2017 8:45 am

They are not afforded protection either, they may show it doesn't interfere even though they don't need to.

Being that it is 10% of the operating frequency a diplexer can be made. When gets less than 2-3% it gets a bit more challenging.
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Re: WBBM 780 to diplex with WSCR 670

Post by Turkeytop » Mon Nov 27, 2017 3:29 pm

Somebody explain to me. Why do they want to make this change? I'm sure there are technical reasons that I don't get.

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Re: WBBM 780 to diplex with WSCR 670

Post by MWmetalhead » Mon Nov 27, 2017 5:37 pm

My understanding is that the existing WBBM transmitter site sits in a prime area for commercial development.

Entercom apparently wants to put the land up for sale. I do not recall how much acreage is involved.
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Re: WBBM 780 to diplex with WSCR 670

Post by Turkeytop » Mon Nov 27, 2017 7:50 pm

So, to be sure I understand this story, Is WBBM physically moving its transmitting facilities to the same location already being used by another station, WSCR?

Re CKLW, my understanding is that a treaty between U.S. and Canada provides for mutual protection in both countries. Somebody tell me if I'm wrong.

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Re: WBBM 780 to diplex with WSCR 670

Post by MWmetalhead » Tue Nov 28, 2017 10:08 pm

"Yes" is the answer to your first question. They will share the tower currently used by sister station 670 WSCR.

I will need to defer as to your second question.
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Re: WBBM 780 to diplex with WSCR 670

Post by Turkeytop » Tue Nov 28, 2017 10:33 pm

Wow. Same tower. I didn't even know that was possible. I thought we were only talking about two towers on the same piece of land.

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Re: WBBM 780 to diplex with WSCR 670

Post by k8jd » Sat Dec 02, 2017 1:47 pm

Yes sharing towers between stations has been done for a long time. Tight LC filters can isolate the transmitters.
Most of the AM stations in Honolulu, where real estate is expensive, are two or three stations on one tower.
I think the station selling the tower and property for developmenl is the main reason. Most of the big AM power stations in Chicago have about the same tower height along the western suburbs.

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Re: WBBM 780 to diplex with WSCR 670

Post by SolarMax » Sat Dec 02, 2017 9:54 pm

Another notable diplexing example is WCBS 880 and WFAN 660 in NYC.
BTW there was a discussion on diplexing/quadplexing in this forum in fall 2015.

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Re: WBBM 780 to diplex with WSCR 670

Post by Marcus » Sun Dec 03, 2017 12:42 am

In Toronto there is Zoomer Radio AM 740 and Ici Radio-Canada Premiere on 860 AM sharing a Tower just off of hwy. 401 near Hornby.

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Re: WBBM 780 to diplex with WSCR 670

Post by Turkeytop » Sun Dec 03, 2017 11:08 am

Marcus wrote:
Sun Dec 03, 2017 12:42 am
In Toronto there is Zoomer Radio AM 740 and Ici Radio-Canada Premiere on 860 AM sharing a Tower just off of hwy. 401 near Hornby.
Thanks for that Marcus. I didn't know that. Was that the arrangement back when CBC Radio 1 was still on 740?

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Re: WBBM 780 to diplex with WSCR 670

Post by MWmetalhead » Sun Dec 03, 2017 6:40 pm

Another notable diplexing example is WCBS 880 and WFAN 660 in NYC.
I did not realize that! For some reason, skywave reception from WCBS is a lot more conspicuous than that from WFAN around these parts.
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Re: WBBM 780 to diplex with WSCR 670

Post by Marcus » Thu Dec 07, 2017 1:59 pm

The tower near Hornby was built in 1937. In 1948 both 740 CBL and 860 CJBC began sharing that particular transmitter site. Later on the CBC made CJBC part of its French language radio network, and the CBC FM signal in Toronto began carrying different English language programming than CBL at 740.

http://www.broadcasting-history.ca/list ... ty-toronto

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Re: WBBM 780 to diplex with WSCR 670

Post by Turkeytop » Thu Dec 07, 2017 2:24 pm

Marcus wrote:
Thu Dec 07, 2017 1:59 pm
The tower near Hornby was built in 1937. In 1948 both 740 CBL and 860 CJBC began sharing that particular transmitter site. Later on the CBC made CJBC part of its French language radio network, and the CBC FM signal in Toronto began carrying different English language programming than CBL at 740.

http://www.broadcasting-history.ca/list ... ty-toronto

I remember when CJBC was converted to French. Made a lot of people unhappy. CJBC carried more of the popular, mass market programs. CBL was more high minded, as Radio II was later to become.

CBC Radio II was good, when it was only available in large cities like Toronto or Montreal. It had a mainly classical music and jazz format. Once they started to expand the network to cover small towns like London, Sarnia and Sudbury, the elitists at CBC Toronto thought that hicks like us out here, would be incapable of appreciating fine programming. They felt they had to dumb it down for us. They gave us the all garage band format.

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Re: WBBM 780 to diplex with WSCR 670

Post by SolarMax » Thu Dec 07, 2017 10:31 pm

MWmetalhead wrote:
Sun Dec 03, 2017 6:40 pm
Another notable diplexing example is WCBS 880 and WFAN 660 in NYC.
I did not realize that! For some reason, skywave reception from WCBS is a lot more conspicuous than that from WFAN around these parts.
Unless there's some serious ionospheric absorption thing going on, WCBS is always solid at night for me, with WFAN usually pretty iffy. WCBS' audio processing also gives them unmistakable punch.

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Re: WBBM 780 to diplex with WSCR 670

Post by MWmetalhead » Sat Dec 09, 2017 10:05 pm

Yup, WCBS and WABC seem to be the easiest to receive AM stations from NYC in southern Michigan after dark.
C'mon iHeartRadio - do the RIGHT thing for once! Please cancel "Rover's Morning Glory" from WBFX in Grand Rapids.

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Re: WBBM 780 to diplex with WSCR 670

Post by Radio Chili » Sun Dec 10, 2017 1:08 am

With most of my nights spent in Grand Rapids, 660 has never 'come in' as good as 770 and 880 has there. In Central FL it's about the same, 770 and 880 are always readable but you hardly ever hear any trace of 660.

Interestingly, I can't ever seem to get 670 from Chicago when I'm in FL but 720, 780 and 890 are there most of the time!

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