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WWJ vs. WJR Signals

R

rfry

The effective radiated power of WWJ in the horizontal plane, at the peak value of its daytime azimuth pattern is about 5.5 X that of WJR.

Even so, the distances to the 2.5 mV/m, 0.5 mV/m and 0.15 mV/m groundwave contours are bit less in that direction for Class B WWJ in the daytime than for Class A WJR in that general direction. Probably this is the opposite of what would be expected.

Both groundwave signals travel across paths with virtually the same ground conductivity, M3 values or not.

Factors in this are:

(1) The WJR transmitter site is located somewhat north of the WWJ site, so the propagation path from WJR to those contours is a little shorter in that general direction.

(2) The groundwave propagation losses for WJR on 760 kHz are not as high as for WWJ on 950 kHz. This is reflected in the paper linked below, which charts the relationships between frequency and groundwave field intensity for several values of transmitter power and ground conductivity.

http://www.thebdr.net/articles/rf/xmit/Contours.pdf

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The difference is verified by the fact that WJR daytime goundwave still stops the scan for a few miles farther than the major lobe than WWJ. At night WWJ enjoys a stronger signal in Northern Michigan, and at times a de facto 20:1 Skywave D/U ratio. Considering that the skywave often is in the 10 mV/m range, and their site NIF is around 3.56 mV/m, even though their is a lot more interference from the 950 in Chicago further north, the signal is very listenable.
 
As correctly pointed out by Schroedingers Cat, the nighttime skywave field intensity of WWJ present at and near the direction of its single, major lobe may be higher than that of WJR in terms of its field intensity, even though the daytime groundwave field of WJR surpasses WWJ in that same sector.

But a more significant and practical measure in the useful nighttime coverage areas of WWJ and WJR is the population counts that they can serve.

The nighttime signal of WJR can be usefully received over a very large geographic area of the US and Canada, containing many more millions of potential listeners than is possible for WWJ.
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