Stephen from San Diego, CA, a reader of Mediumwave Oddities - Transmitter Power, wrote in with the following question:
"What stations actually are authorized with a HIGHER power at night than they are allowed in the daytime? I'll mention one - 760 KFMB San Diego, CA, about 7 miles from me. In the daytime they're only allowed a paltry 5KW omnidirectional, but at night they step up to 50KW."
An interesting question. And you mentioned signal patterns, all-important in the differences between daytime and nighttime mediumwave coverage.
I tweaked my database program Radio Data MW and came up with the following results:
73 US stations run higher power at night than during the day.
WLAN's main competitor is WZHF-1390 (5KW), in Arlington, VA, a mere 92 miles away to the south-southwest. How does an 1100 watt station co-exist with a 5KW station at night when they are only 92 miles apart? Examining the tower pattern plots, you will find that WLAN in Lancaster, PA is exactly in a deep notch of WZHF's nighttime pattern.
Shown are nighttime pattern plots for San Diego's KFMB-760 and Avalon's KBRT-740, generated by Radio Data MW.