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WBBM AM to diplex with WSCR

Schroedingers Cat said:
The thing that bothers me from a Radio Hobbyist/Radio Historian perspective is that the Day facility with 35 kW falls short of the efficiency of a 50 kW Class I-A/A facility, being 1581 mV/m inverse field at one mile, vs. the Historical Class I-A minimum inverse field efficiency of 1591 mV/m at one mile. The Night 42 kW pretty closely matches most Class I-A/A inverse field.
Click to expand...

Your calculations show a 0.1dB change in field strength, which is not even measurable with any reliability in the far field. The change between 50kW and 35kW is 1.5dB, the difference between 40kW and 35kW is 0.8dB, both of those changes are measurable. Neither difference would be audible in the field with an AM receiver's limiter above threshold. The change in facilities would be more interesting in terms of RF bandwidth performance, which relates to audio processing and received apparent loudness. It's entirely possible that the new signal will be louder, and perceived as stronger, but it will be arguably identical from a listener-perceived field strength standpoint.
 
I was just comparing the 1581 mV/m @ 1 mile to the 1591 mV/m @ 1 mile Class I/A MINIMUM for 50000 watts in the above case. The old tower had an efficiency of 1768 mV/m @ one mile. New rules soon may allow it to go back to old comparable levels toward WSGW and other stations. I was trying to do a direct comparison in the horizontal inverse field. 1581/1768=0.894. 0.894^2=0.79944. 10 log 0.79944=0.97 dB~1 dB FROM THE TOWER. The Lake Michigan coasts are up to 4.5 miles further away because the WSCR tower is 4.5 miles (actually 4.58 miles) further away. Toward the East, it is about 3 miles further away. I will do further calculations for the loss at the Gold Coast, Chicago Resort Land in Michigan, and SE Michigan. That will take me a while. There are ways to get around this, a DA, rule changes that might allow a nondirectional increase in power, and measured conductivities. But the loss IS significant in those areas. I should also include calculations in the ORD/NW suburban areas.
 
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They should run radials to determine the measured conductivity in critical directions to see if they can get closer to 50000 watts Day now. Over in 60068, it will fall from the WGN FI range to the WMVP (WCFL) FI range.
 
Since the License to Cover has been issued, I would assume they are using it now. If they weren’t, competitors would be out at the old WBBM site with FI meters and taking videos to turn them in. That’s what’s happened to the old friendly competition and camaraderie that existed between competitors in the early days, even the first 50 years, of broadcasting.
 
It appears they are broadcasting from the WSCR site in Bloomingdale since yesterday, June 12. They have also turned off their HD signal when I checked yesterday.
 
Barry Mishkind said in this quote that a Class A should NEVER use an antenna higher than 200 electrical degrees. The "new" WBBM site is 211.7 degrees. It's not just DXers, but people within the Chicago Radio Market, who are affected by fading. And further out is a big part of their listeners, and WCFS may not come in that well either at the further out places in the market.

And you can't depend on one or a few days Critical Hour and Night test listening to detect a problem with high angle skywave self interference fading.

http://www.durenberger.com/documents/STATIONUPDATEDETAIL.pdf

Barry Mishkind's Quote:

"225 degrees might be OK for a Class C which is trying to get the max out of its 1 kW (probably reduced to 0.5 kW with a tower that tall), but a Class A should never use a single section tower taller than 200 degrees. A 300 degree two-section tower which is anti-fading is OK, a Class A station in the 1500s
should seriously consider a Franklin, which is 360 degrees tall and is about 510 mV/m/kW at 1 km.
225 degrees is about 440 mV/m/kW at 1 km, but the fading problem is severe for a Class A."

A skirted redesign may be in order.
 
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Schroedingers Cat said:
Barry Mishkind said in this quote that a Class A should NEVER use an antenna higher than 200 electrical degrees. The "new" WBBM site is 211.7 degrees. It's not just DXers, but people within the Chicago Radio Market, who are affected by fading. And further out is a big part of their listeners, and WCFS may not come in that well either at the further out places in the market.

And you can't depend on one or a few days Critical Hour and Night test listening to detect a problem with high angle skywave self interference fading.

http://www.durenberger.com/documents/STATIONUPDATEDETAIL.pdf

Barry Mishkind's Quote:

"225 degrees might be OK for a Class C which is trying to get the max out of its 1 kW (probably reduced to 0.5 kW with a tower that tall), but a Class A should never use a single section tower taller than 200 degrees. A 300 degree two-section tower which is anti-fading is OK, a Class A station in the 1500s
should seriously consider a Franklin, which is 360 degrees tall and is about 510 mV/m/kW at 1 km.
225 degrees is about 440 mV/m/kW at 1 km, but the fading problem is severe for a Class A."

A skirted redesign may be in order.
Click to expand...

This is very unscientific but I was in Eastern Ohio for a couple of days early this week and I didn’t notice any difference in WBBM’s signal at night. During the drive back I heard BBM in western Ohio all the way into the Chicago area during the day with no noticeable difference in the ground wave signal from what I had heard at these locations in the past. For the record when I was in Eastern Ohio at night WLS had the strongest Chicago Skywave. WSCR was getting lots of interference from Cuba.
 
One of the things we notice over here in Michigan is all the fading in the signals of the new 50 kW stations with broadside directional designs. Broadside design makes the high angle skywave stronger and causes more fading, whereas inline and slight dogleg endfire designs lessen high angle radiation and fading. The reasons for broadside designs may be the RMS/RSS ratio and RMS related standard pattern null depth, but FCC engineers say that theoretical patterns are actually more accurate in predicting null depth in properly maintained arrays. But you have to do long term listening to hear the fading. It's not every night, it's more prevalent certain seasons and years. It can be very bad some nights.

I suspect that as the year goes by, you will notice some nights its pretty bad, and outer market counties will be most noticeable, more so than Ohio. You have to look at the vertical pattern profile to see the high angle lobes, and translate to affected distances.
 
Speaking of SE Michigan, WWJ puts in a solid day signal in Eastern Ohio. That 50KW 5 tower array does well for them. I haven't been over that way in quite awhile.
 
Go to this link and look at Page 2-134 for the horizontal efficiency gain or loss of various 2 tower patterns with spacing and phase. The vertical radiation characteristics of various heights are shown on other pages. It is often difficult to see on graphs of vertical radiation characteristics for various heights.

https://www.americanradiohistory.com/Archive-NAB-Engineering/NAB-5th-Edition/Section-2-NAB-Engineering-Fifth-Edition-3.pdf

The VRCs with tower height are shown on 2-116 and 2-117, every 5 degrees.
 
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Schroedingers Cat said:
Go to this link and look at Page 2-134 for the horizontal efficiency gain or loss of various 2 tower patterns with spacing and phase. The vertical radiation characteristics of various heights are shown on other pages. It is often difficult to see on graphs of vertical radiation characteristics for various heights.

https://www.americanradiohistory.co...Section-2-NAB-Engineering-Fifth-Edition-3.pdf

The VRCs with tower height are shown on 2-116 and 2-117, every 5 degrees.
Click to expand...

I’m glad those NAB papers and books are useful! Did you see that about 20 of the Proceedings volumes were just added?
 
The 10% skywave at 50 miles in the CH right before sunset would be about 0.95 mVm. The ground wave according to M-3 would be about 7.1 mV/m. So as the phase varied, the field strength would vary from about 6 mV/m to 8 mV/m, along with the phase distortion associated with the phase change.
 
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I'll have to check that out. Thanks, David, for all of this. I don't know of another industry so well documented. I guess Carl Smith composed a lot of those graphs and formulae.

Didn't realize until this past year that Carl Smith and his ancestors once owned the "American Gothic" house in Iowa in the Grant Wood painting. My favorite joke, knowing this detail, is that Carl Smith originally envisioned the three tower in line directional antenna array design while contemplating the tines in that pitchfork!

The other value is to get a historical perspective on how regulations changed. This is particularly useful in explaining to people how so many FM stations became "short spaced", as though the stations themselves created it and not the changing regulations, or that one station is short spaced, but of course not their's, but the other station.
 
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