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WJR vs. WWJ Fields at Utica, MI

The technical side of broadcasting. Think IBOC is a sham? Talk about it here! How about HDTV? Post DX reports here as well.
CK-722
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Re: WJR vs. WWJ Fields at Utica, MI

Post by CK-722 » Fri Jun 14, 2019 12:17 am

Thanks, Rich. Innate, I think this graphing software presents in a form that is unusual. I think it shows what the FI would be along points of a circle equidistant from the old WWJ tower, about 14 miles away. I don't know why the first circle is 0 and not the center of the graph. That would suggest that you could have an FI less than zero. At first I thought it was logarithmic, like hams use in antenna polar plots. I like linear FI polar graphs of relative field, and that is what the FCC almost always uses with broadcast exhibits. But indeed it has the appearance of being much less directional than it was.

No doubt that when the DA was built in 1935, it was thought that they would have the shallow 1 kW equivalent nulls toward the COL. In fact, any change in operating parameters that resulted in more equal field ratios would cause the nulls to be deeper, even theoretically zero. When DAs were built in a less ideal direction from the COL, this is what happened. This is also why some lower power center city nondirectional Night facilities exist to this Day.


Is THAT where they got the idea for the 486-SX?

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Rich
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Re: WJR vs. WWJ Fields at Utica, MI

Post by Rich » Fri Jun 14, 2019 6:45 am

CK-722 wrote:
Fri Jun 14, 2019 12:17 am
... I think it shows what the FI would be along points of a circle equidistant from the old WWJ tower, about 14 miles away.
Correct.
I don't know why the first circle is 0 and not the center of the graph.
I set the lower limit of the scale to less than zero field to give more resolution to the lower values in the plot, but no such sub-zero field values are possible. Sorry for the confusion that produced.

Radiated fields vary as the square root of the change in radiated power. For example, reducing radiated power from 10 kW to 1 kW is a 10:1 ratio, but (other things equal) that reduces the radiated field only by √10. A 10 mV/m field at 10 kW ERP becomes a 3.162 mV/m field at 1 kW ERP.

Looking at the detailed output of that NEC data shows a field of about 8.2 mV/m at N170°E on the pattern. That reduction from the maximum 27.4 mV/m is 8.2/27.4 = 0.299X, approx, or about 10.5 dB. So radiated power also had to decrease by a factor of 10.5 dB. That is an ERP reduction to 8.9% of maximum ERP, which is a pretty good "null" in radiated power at that azimuth.

So the graphic is correct, but takes some mental gymnastics to understand, completely.

(Last edit at 11:59am June 14 2019)



CK-722
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Re: WJR vs. WWJ Fields at Utica, MI

Post by CK-722 » Fri Jun 14, 2019 1:18 pm

How the taller tower became 186 degrees, near the theoretical ideal.

When WWJ was on 920 (from the late 1920s to 1941), they built a 1/2 wave antenna on 8 Mile Rd. That was 180 electrical degrees. When they moved to 950 in 1941, that electrical height became 186 degrees.

In the meantime, before they went directional around 1935, it was 5000 watts Day/1000 watts Night nondirectional from that tower. They added the 400 foot, 139 degree tower when they went to 5000 watts directional at Night, around 1935.
Last edited by CK-722 on Fri Jun 14, 2019 2:04 pm, edited 1 time in total.


Is THAT where they got the idea for the 486-SX?

Same (x, y, z), different (t)

Your bullet missed my trial balloon.

RTN Price. Not guaranteed. As of 12:30, 157.71 Down 0.22.

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k8jd
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Re: WJR vs. WWJ Fields at Utica, MI

Post by k8jd » Fri Jun 14, 2019 1:22 pm

innate-in-you wrote:
Wed Jun 12, 2019 11:39 pm
Sadly, I think only two years ago the FCC site still had the full engineering for the Royal Oak Township TL.

the basic design can still be seen at fccinfo.com. The two tower array had a one taller Blaw-Knox tower and a shorter Blaw-Knox tower nearly south of it actually in the direction 170° azi.
The nulls have just slightly less than 20% of the maximum field strength, thus about 4% of the peak ERP.

I'm sure someone on here who has actually designed a DA could replicate the FCC's engineering using the figures on fccinfo.com.

I strongly doubt that the nulls were anywhere near 1000 watts ERP.
I grew up near I-94 and Cadieux on Detroit's East Side.
On my crystal set, WWJ was plenty strong by day, and absolutely dead when they went to night pattern. A good radio with tubes or transistors could still pick them up, but I could hear other voices on the channel.

For those saying "They were not Blaw-Knox - they were not like WLW". Blaw-Knox also made square form towers.
I recall seeing a plot of the WWJ night time coverage and it looked more like an inverted pear shape than any sharp nulls on a lot of other patterns in the area.



CK-722
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Re: WJR vs. WWJ Fields at Utica, MI

Post by CK-722 » Fri Jun 14, 2019 3:58 pm

As far as I can see, the pattern can be reconstructed from the data on fccinfo, except for perhaps the augmentation data. I have old databases, in the AMDATA.DAT format, but it would take me a while to find them. I'm an "archiver", like my cousin's husband, who still has his original COBOL code line printouts in his closet.


Is THAT where they got the idea for the 486-SX?

Same (x, y, z), different (t)

Your bullet missed my trial balloon.

RTN Price. Not guaranteed. As of 12:30, 157.71 Down 0.22.

Artificial Intelligence is a Child that needs a Parent to guide it through.

Rich
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Joined: Sun Dec 26, 2010 3:28 pm
Location: Illinois
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Re: WJR vs. WWJ Fields at Utica, MI

Post by Rich » Fri Jun 14, 2019 6:22 pm

CK-722 wrote:
Fri Jun 14, 2019 3:58 pm
As far as I can see, the pattern can be reconstructed from the data on fccinfo, ...
Below is an easy way out by taking the pattern from the fccinfo page and adding some text labels to it.

Image



innate-in-you
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Re: WJR vs. WWJ Fields at Utica, MI

Post by innate-in-you » Fri Jun 14, 2019 7:08 pm

Nicely done.

There were no zero nulls, but nulls nevertheless.

My understanding is that this plots the field strength in volts relative to the peak field, in this case, 350°.

The nulls, primarily protecting Houston and Philadelphia (and saving many stations in the Eastern US from being blown out of the water) basically affected places like Grosse Pointe and Wayne.

Plots like this are usually in mV/m. This would imply that in terms of power (as opposed to voltage) 25 times as much power was directed at Rochester than was directed at Grosse Pointe or Wayne. [(max field/.2 max field)squared].

A personal observation: Back in the day, my wife and I would go camping up north. When we wondered what may be happening downstate, we would listen to WWJ for a few minutes. It was audible, even though it was on a regional channel. The Chicago station could be heard under it at times, but never blew out WWJ.



Rich
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Re: WJR vs. WWJ Fields at Utica, MI

Post by Rich » Sat Jun 15, 2019 10:06 am

Here is a study using NEC4.2 set for an Earth conductivity of 8 mS/m:
  • The WWJ 186° radiator at 8 Mile Rd used alone, and driven with 5 kW would generate about a 20.6 mV/m field in Grosse Pointe, MI (a 14 mile path at N107°E).
  • The 186° radiator used alone and driven with 1 kW would generate a field of 9.2 mV/m in Grosse Pointe.
  • If the WWJ DA array had a maximum gain 3 dB greater than the 186° radiator alone, the array was driven with 1 kW, and the pattern maximum faced Grosse Pointe, then the field there would increase to 13 mV/m.
  • The WWJ DA pattern oriented as installed has a relative field of about 0.18 toward Grosse Pointe, therefore the field for these assumptions would be 0.18 x 13 mV/m = 2.34 mV/m.
  • If the WWJ DA array as installed was driven by 5 kW, the field in Grosse Pointe would increase from 2.34 mV/m to 5.23 mV/m.
For comparison and over a 21.5 mile path at N46°E, WJR has a 24 mV/m field in Grosse Pointe, 24/7.



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