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WLW 500 kW Directional vs. 50 kW Nondirectional 5 mV/m and 1 mV/m 50% Skywave Map
- Thread starter Schroedingers Cat
- Start date
There are quite a few megawatt stations outside of the Western Hemisphere. The day coverage depends entirely on the ground conductivity in the area. If you look at the WJR map in this thread, multiplying the power by 10 only increases the coverage area by a little more than double in total square miles. Going from 500 kw to two megawatts doubles the land area.
The reason for such high power is to avoid having multiple transmitters for government stations. The objective is to reach as much of a country as possible with as few transmitters. But with today's noise levels, that's no longer practical as those distant transmitters just can't overcome the man-made noise. But the goal of those high-power AMs is to cover much of a small nation... not worth much in the era of FM and the Internet.
At night, people watch TV. Practically nobody listens to distant radio stations.
And where the signal has to cover that sandbar called Long Island, it only gets a few dozen miles!
The transmitter power multiplier at the common point of a directional array can be well below the multiplier for the maximum effective radiated power of the array compared to a non-D radiator, though.
The plot below is an extreme example of this, where WWJ radiates over 380 kW at the peak of their main, daytime lobe — which is ~7.6X more than the 50 kW power they apply to the common-point of their array.
If WWJ was licensed for 500 kW of power at the common point of that array then their maximum, daytime ERP would be ~3.8 megawatts.
It probably wouldn't have made Les Biederman, Harvey Klann, and Richard Hunt very happy, but the outlying areas to those Daytimers and Class IVs with 250 watts Day and Night before circa 1960, along with the measured, proven, low conductivity now documented in many applications, it sure might have helped giving service to those most rural areas. I had a loaned field strength meter quite a few years ago or so, and I measured WJR, WWJ, and WFDF (at 5 kW from the old Burton site, and close to the same with 50 kW from the Carleton site) all at about 50 uV/m. Rich and I have theorized that the conductivity near the TL affects the attenuation more than at the far end of the signal path, and that is where the signal likely took a dive below M-3 prediction.
It would take (50X25)=1250 kW equivalent to get a PREDICTED M-3 0.5 mV/m Groundwave near Indian River, MI. You could get that with two towers, but I don't know if you could have only 50 kW equivalent toward Toronto with just two towers with a cardioid type pattern like that shown. If the maximum were at 330 degrees, it would be close to the equivalent of 500 kW toward Toronto at 60 degrees true. So I think we both agreed a while back that the pattern on that map is pretty much fictional.
One of the patterns in the upper left quadrant of the graphic below might produce the 500 kW daytime contour on the WJR proposal — with some legitimate "tweaking."
Earth conductivity on the paths toward Toronto are a lot higher than toward the west and northwest areas of lower Michigan, and that needs to be factored in.
It would take more than two towers to design that pattern. We could reverse engineer the distances and recreate the actual pattern. That would give a better idea, if more application information is not available.
That would be interesting, SC. I don't have any of the details of that proposed array, unfortunately. I wonder if two towers might actually do the job, maybe even if one was parasitic.
Probably the M3 chart values should be used when backing into what would/might have worked, when that 500 kW, 0.5 mV/m contour was proposed.
The issue was not the population... it was who got there first.
Both Cincy and DC got a high-band 1-B (1500 and 1530) but Crosley's early interest in radio dating back to 1921 got him one of the "big 1's" when the FRC started regulating and creating classes of service.
Why did Des Moines get a 1-A, while Milwaukee got no 50 kw stations at all in that period? And Florida got no 1-A or 1-B at all, as in that era alligators could not file for an FCC license (although some believe both gators and crocs can apply today).
The problem is that the WJR Coverage Map with 50 kW was apparently, according to one of the engineers I called, at least partly based on Measured Contours. I remembered his name for a time, but no longer.
Have you ever seen a LEGIBLE Conductivity Map of Canada? I know there are areas of 15-20 mS/m in the Windsor, Sun Parlour, and Sarnia Area. One of the WTCM applications, I think it was the first of the relatively recent ones, for 15 kW Daytime, that showed CKWW radial conductivities that were around 20 mS/m.
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The best one I've found is in the ITU library, although it is fairly primitive looking compared to what the FCC has published lately. Below is a clip showing conductivities for a section of Ontario.
I've heard more than one report that WFAN, WABC, and WCBS can be heard all day with a weak but listenable signal in Bermuda.
That is true. I heard a sound file that someone sent me about 10 years ago when he was in Bermuda in June. He got several east coast stations at noon including the ones you mentioned and there were a few others. I think WINS was among them.
I was in Punta Cana just recently (about a month or so ago) and WFAN/WCBS were both audible on the beaches there at night. WCBS was stronger.
Years ago I saw a letter exchange between one of the Crosley engineers and a EE at Blaw Knox. Powell had insisted on having an antenna built at WLW for maximum skywave, so there was a lot of back and forth on how to achieve it.
Eventually the Class A stations decided that not interfering with their own signal in the cancellation zone of a radiator taller than about 195° was preferable to gaining a few tenths of a decibel of skywave field out beyond the (self-interference-free) cancellation zone.
The great majority of 50 kW, non-D, 24/7 "legacy" AM broadcast stations now use tower heights of about 195°.
The great majority of 50 kW, non-D, 24/7 "legacy" AM broadcast stations now use tower heights of about 195°.
Those original coverage maps showing field strength borders of .5mVm are a lost classic, because it's wholly impractical that given the noise floor today, anyone could receive a signal attenuated that much.
Class As were and are protected to the 0.1 mV/m ground wave. There are at least several of those coverage map images available online. Even smaller stations had coverage maps that show the 0.5 and 0.1 mV/m contours, especially those prepared by Kear and Kennedy.
0.5 mV/m signals are still listenable away from electrical wires, especially remote store parking areas away from stores, and in rural areas.
In the 1960 NAB Engineering Handbook, it even shows a recommendation that city factory areas receive 25 mV/m or more. I can tell you for sure that inside heavy manufacturing plants and deep inside malls, you need 100 mV/m outside those buildings to be heard well inside. And you always did.
0.5 mV/m signals are still listenable away from electrical wires, especially remote store parking areas away from stores, and in rural areas.
In the 1960 NAB Engineering Handbook, it even shows a recommendation that city factory areas receive 25 mV/m or more. I can tell you for sure that inside heavy manufacturing plants and deep inside malls, you need 100 mV/m outside those buildings to be heard well inside. And you always did.
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