Have you ever heard of an AM station that INCREASES power at night?
I just did. It's WHBY licensed to Kimberly, Wisconsin.
With a good daytime power of 20kW, the station UPS the power after dark all the way to 25kW!
They have a very smart antenna location and pattern, serving THREE major Wisonson cities with their beam: Oshkosh, Appleton and Green Bay.
Yes, KFMB (760 kHz, San Diego) is licensed for 5 kW non-directional during the day, and 50 kW directional at night. Most of their nighttime power is aimed at the Pacific Ocean.
The null in the nighttime pattern of KFMB protects the nighttime skywave coverage of WJR, Detroit -- who is the U.S. "Class A" station licensed for 50 kW on 760 kHz, non-directional 24/7.
Here's a link to KFMB's patterns:
http://www.freeimagehosting.net/i7pef
Another station that does this is WDIZ-AM 590 in Panama City, FL.
It runs 1700 watts daytime and 2500 watts at night.
What's the idea behind increasing power after dark?
I mean, the more common practice of reducing power is to diminish the risk of a sky wave clash with full time stations, so what's this other thing of boosting power at night?
Carl - the KFMB daytime pattern is non-directional at 5 kW. That was the maximum power they could use during the daytime in order to protect other stations on 760 kHz that were a lot closer to them than WJR, Detroit. This was their "legacy" assignment from the FCC.
Later KFMB was allowed to stay on the air at night, with a directional pattern to protect WJR from the KFMB skywave interference, and to use 50 kW (with most of the power directed to the Pacific Ocean).
There are four other U.S. AM stations west of the Mississippi using 760 kHz at night, and they all have to use very low power and directional antennas to protect WJR.
KFMB is a special case because of the large distance between San Diego and Detroit.
I guess there's no way to emulate the nighttime power raise on Part 15 AM.
We could direct most of the power toward the lake in the park