Groundwave vs Skywave

Can someone explain how groundwave can cancel out skywave?

I was driving back from Laredo one night (clear night, summer) and I tuned into XEG 1050AM, and to my dismay, I could not pull it in, even though I was only 133 miles from the tower. I am able to pull in XEG when I am in Victoria, Port Lavaca, Houston, Austin, Baton Rouge, etc.

AM signals travel better at night, so of course if we were talking daytime coverage area, the signal of XEG fades about 45 minutes south of Laredo.
At night, however, XEG can be heard throughout much of the southern portion of the US.

Does the XEG groundwave signal, even at night, only carry to about 45 miles south of Laredo, then for about 60 miles, the signal disappears (because of the fighting between groundwave and skywave), and then after approximately 60 miles, does the skywave signal win the battle and carry across far distances, but in the opposite direction of the tower? I estimated 60 miles because I began to get a usable signal in between Freer and George West.

Thanks in advance for any explanations given.

There is a cancellation zone where the groundwave and skywave duke it out making a mess of the received audio. IIRC this is due to the Groundwave and Skywave signals being out of phase. I can notice the effect when KRLD switches to their night pattern.

LibertyNT said:

There is a cancellation zone where the groundwave and skywave duke it out making a mess of the received audio. IIRC this is due to the Groundwave and Skywave signals being out of phase. I can notice the effect when KRLD switches to their night pattern.

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Is this why WOAI is hard to get in Houston?

If you're in St. Louis listening to KMOX, that signal will get fuzzy at 60 miles away as the groundwave dissipates, then totally disappear at 80 miles, THEN blast back at 120 miles as the skywave asserts itself -- then disappear again at 150 miles, only to reappear at 200 miles -- which explains why you can hear KMOX here in Houston on occasion at night.

When WSM had their tower built, it was too tall and caused signal cancellation near a major metro at night..the tower was reduced in height and the signal cancellation area was moved out west of the area in a sparsely populated area....back then anyway

ThatVoice22 said:

If you're in St. Louis listening to KMOX, that signal will get fuzzy at 60 miles away as the groundwave dissipates, then totally disappear at 80 miles, THEN blast back at 120 miles as the skywave asserts itself -- then disappear again at 150 miles, only to reappear at 200 miles -- which explains why you can hear KMOX here in Houston on occasion at night.

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I love this post! I've read it at least eight times now.

What you've described is very similar to XEG 1050AM Monterrey's signal habits.

The Rimshot said:

I love this post! I've read it at least eight times now. What you've described is very similar to XEG 1050AM Monterrey's signal habits.

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Thanks, Rimshot - (I appreciate your screen name and its self-deprecating humor) Similar logic applies to Continuous Wave's comment on Nashville's WSM - - at Night, there's a literal up-n-down skywave that emanates from the broadcast tower and bounces off the ionosphere to re-appear at ground level every so many miles, so you might get a great signal at 200 miles away, but not-so-much at 80 miles away. This condition is most noticeable from the big 50KW signals and is affected by atmospheric conditions, local and distant. This explains why WOAI, a 50 KW boomer in San Antonio, is not well received here during the day coz the groundwave has dissipated, but not at night either -- but if ya go another hundred miles away from Houston, WOAI will come in just fine in Oklahoma, Louisiana, or New Mexico. Similarly, the XEG signal from Monterrey, Mexico is another example of here-today, gone in 60 miles, and mysteriously back-again at 100 miles at night.

I'm not very technical when it comes to AM stations, but I thought the waves always transmit through air and not ground. LOL