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FCC grants WBBM a CP to move transmitter site

DavidEduardo said:


The "new" tower for WBBM is more efficient. It produces the equivalent of 50 kw from the old tower.

Except for differences based on individual listener distances from the old and new sites, there should be no difference in signal strength in the service area.
Click to expand...

Agree in part, disagree in part.

The really smart AM engineers I know (because that ain't me) tell me to expect some real-world effects at the edges of the market because the taller tower will produce a different vertical takeoff angle for the skywave - which will mean the groundwave-skywave cancellation ring will move (closer to Chicago, IIRC).

Also, the really smart AM engineers I know tell me, and not with much pleasure, that most of their domestic workload these days consists of telling old-line AM owners whether it's feasible to move away from their legacy sites to locations where the land is less valuable. Which is to say, we'll be seeing more moves like this - and probably more along the lines of WMAL (which will significantly impair the in-market signal, especially at night) than WBBM (where you'll have to look really hard to notice a change.)
 
fybush said:
Agree in part, disagree in part.

The really smart AM engineers I know (because that ain't me) tell me to expect some real-world effects at the edges of the market because the taller tower will produce a different vertical takeoff angle for the skywave - which will mean the groundwave-skywave cancellation ring will move (closer to Chicago, IIRC).
Click to expand...

I should have clarified: the differences inside the Chicago MSA are likely to be minimal, if any. And, as you say, the signal strength may remain about the same but the fringe interference may increase.

There may be a reduction of distance to the skywave cancellation zone based on the change in the electrical height of the tower. A good example of this was the lengthy period when KFI was on a shorter tower following the airplane strike to its facility. This moved the cancellation zone inwards from about 120 miles (Indio to Desert Center on I-10) to about 60 to 80 miles (Calimesa to Cabezon).

The KFI "emergency" tower was significantly shorter than the fallen one... on the order of a quarter wavelength shorter. The WMAQ tower is a smaller amount taller, and the real issue at that point (where 180° is exceeded) is likely more in the effects of the secondary lobe, which at a glance does not seem to be something to worry about inside the MSA.

And I am guessing that, given the fact that night listening is low and not easily monetized, Entercom figured that the rumored $100 million for the land is better than a few miles of coverage. This also may be a reflection on the projected future value of AM in general.

I do wonder how they will feel in December, January and February when around half of AM and PM drive are in darkness and the secondary lobe come down in Hammond or Morris or Kenosha and makes in-car listening disagreeable.

Probably, though, the Entercom folks know how much listening now is to the FM and they don't see that where the AM is endangered in the fringe areas is precisely where a downtown FM is approaching or beyond the range of usability. I suspect that the AM usage in the farthest outlying counties is much higher than near the Loop, and that is the area where the move may be counterproductive.
 
fybush said:
Which is to say, we'll be seeing more moves like this - and probably more along the lines of WMAL (which will significantly impair the in-market signal, especially at night) than WBBM (where you'll have to look really hard to notice a change.)
Click to expand...

The one thing the two stations have in common is they have FM simulcasts, which is basically what the FCC is promoting.

Sooner or later, the AM dial will be a lot like a burnt out inner city ghetto. Empty dilapidated buildings where there once was a bustling neighborhood.
 
Even if the tower heighths and efficiencies were fully identical,
one and a fraction db is or are absolutely undetectable,
even with plenty of QRM, QRN, QSB, and a string of other Q's.
 
ai4i said:
Even if the tower heighths and efficiencies were fully identical,
one and a fraction db is or are absolutely undetectable,
even with plenty of QRM, QRN, QSB, and a string of other Q's.
Click to expand...

Scott does have a point regarding radiation angles, and the possibility that the night skywave cancellation zone could move inwards compared to the old tower.
 
Why cannot the top X number of feet of the tower be detuned at 780
(perhaps removed and put back on top of a ceramic insulator)
with an LC bypass just for 670?

This is RADIO science but it is NOT the proverbial ROCKET science.
 
Well I see alot of AM Band scans now

Sounds like 670 & 780 still have HD on

Are they turning it off when WBBM moves?
 
DavidEduardo said:


Entercom does not seem partial to AM HD, so one can always hope.
Click to expand...

WSCR seems to be turning off their HD during pre-dawn hours from time to time. WBBM appears to be more inclined to go 24/7 with their noisemaker.
 
ai4i said:
Why cannot the top X number of feet of the tower be detuned at 780 (perhaps removed and put back on top of a ceramic insulator) with an LC bypass just for 670? ...
Click to expand...
However (other things equal), doing so would slightly reduce the groundwave field of WBBM relative to their using the full height of the WSCR tower as it is.

But if the radiating length of the WSCR tower was reduced to about 194° for WBBM, then the distance to the center of their self-cancellation zone for their nighttime groundwave and skywave would be about the same as it is/was before the move. Using the unmodified WSCR tower by WBBM will move the WBBM cancellation zone closer to the tower site than it is now.

Some reviewers have the opinion that at this point, WBBM must not be very concerned about optimizing their relatively self-interference-free nighttime (secondary) coverage area.

Below is a pattern analysis for the use of the unmodified WSCR tower by WBBM. Compare the amount of radiation at an elevation angle of about 57° for WBBM using the existing WSCR tower vs. their using a 194.1° tower.

WSCR_WBBM_Elev_Pat_Compare.jpg
 
The radiation angle looks most ideal for "The Score",
but if they were to clip the tower at that relative height as I suggested,
their groundwave into Chi-town would of course suffer,
and that is the most important consideration of all.
 
Same applies to WGN site which is just a mile north of the WBBM site. Would not be surprised if they eventually move out as well down the road. Question is where would they go?

I don't think WBBM is using the WSCR site yet.
 
CADXER said:
Same applies to WGN site which is just a mile north of the WBBM site. Would not be surprised if they eventually move out as well down the road. Question is where would they go?
Click to expand...

I agree 100%. I think the process will begin immediately once they get WGN's future ownership question(s) settled.
 
This past weekend (Saturday morning and Sunday morning) both WBBM and WSCR were off the air between 1 am and 4:30 am. Most likely work was being done for the upcoming move by WBBM to the WSCR transmitter site.
 
Both WBBM and WSCR were off the air the past two nights again. Most likely working on the diplexing setup. Unfortunately I missed the silent period to do some DX.
 
WSCR and WBBM off again this past weekend during the early morning hours on Saturday and Sunday. Only Cuba on 670 heard with positive ID. No trace of any signals on 780. Conditions were quite poor.

The move is getting closer. I drove past the WBBM site last week and noticed several heavy duty construction vehicles parked by the transmitter site entrance.
 
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