Information please; history of AM Daytimers

[R. Fry]

The Radiolocator pattern for WJR linked below shows their 0.5 mV/m contour near Grand Rapids (in magenta) at only a short distance more than shown for CKLW's 0.5 mV/m contour on their QSL card.  But that close an agreement would be unlikely, due to the difference in ERPs from the two stations toward that sector, and because the path from WJR is about 17 km shorter.

(Later) The FCC MW propagation curves when used for WJR show a distance of about 162 miles to their 0.5 mV/m daytime contour for 8 mS/m conductivity.  According to the M3 chart, that is the conductivity along the path from their tx site along a radial through Grand Rapids.

This FCC value of 162 miles agrees well with the Radiolocator plot for WJR's 0.5 mV/m contour on that radial.

[Schroedingers Cat]

In central Michigan, many recent applications online show much less than 8 mmhos/m. 

With the outside vertical (actually 20 feet of twinlead twisted together from an outside TV antenna) and a preamp, you could also get WIND, WLS, WCFL and many others quite well.

[R. Fry]

In central Michigan, many recent applications online show much less than 8 mmhos/m.

Just to note that, whatever the real earth conductivity, the propagation paths from WJR and CKLW through Grand Rapids are nearly aligned in azimuth.

So regardless, CKLW could not ~match WJR's daytime field in/near Grand Rapids as shown on the CKLW QSL card, given CKLW's significantly reduced ERP and longer path on that radial when compared to WJR.

[Schroedingers Cat]

If these were real measurements of CKLW, I suspect that there might have been some daytime skywave involved.  I can't see it either, given that CKLW's major lobes are the only places where the inverse field exceeds WJR's.

[gr8oldies]

Sometimes you have to take maps made to promote sales with a grain of salt though CKlW's map was pretty dead on for Ohio. WJR was the weaker of the 2 at my Ohio location but they were even in Lima

[R. Fry]

Sometimes you have to take maps made to promote sales with a grain of salt...

Agreed.

... though CKLW's map was pretty dead on for Ohio. WJR was the weaker of the 2 at my Ohio location but they were even in Lima

Lima is located at roughly the same distance, and along roughly the same radial to/from both WJR and CKLW.  The location of Lima is rather well up on CKLW's major daytime lobe toward the SW, so for that ~107 mile distance and regardless of the real ground conductivity, CKLW could reasonably have somewhat greater daytime field intensity there than WJR.

Below are the groundwave values for both facilities in/near Lima, based on the FCC M3 map.

Daytime

   CKLW  1.99 mV/m
   WJR 1.44 mV/m

Nighttime

   WJR  1.44 mV/m
   CKLW  0.35 mV/m

RF

(edit) added the distance