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AM Station power up/down times?

N

nocomradio

Guest
I am curious, as a non-radio station owner/operator:

I listen to WKCW 1420 AM here in VA in the mornings. I've only started doing this regularly in the last month or so as I have to commute a couple times a week. I leave home at around 7:00 AM and it is usually around 7:30 AM when they switch from night to day power again. The time isn't consistent however, with some mornings as early as before I leave to as late as nearly 8:00 AM. This is a fully automated station, as I pass right by it and there isn't a soul at the place and no live voices. Also, the sun is breaking the horizon before they make the power switch.

My question is, is there a specific time when AM stations are supposed to switch from day to night and night to day power? If its an automated station, then why the wild variation?
 
nocomradio said:
I am curious, as a non-radio station owner/operator:

I listen to WKCW 1420 AM here in VA in the mornings. I've only started doing this regularly in the last month or so as I have to commute a couple times a week. I leave home at around 7:00 AM and it is usually around 7:30 AM when they switch from night to day power again. The time isn't consistent however, with some mornings as early as before I leave to as late as nearly 8:00 AM. This is a fully automated station, as I pass right by it and there isn't a soul at the place and no live voices. Also, the sun is breaking the horizon before they make the power switch.

My question is, is there a specific time when AM stations are supposed to switch from day to night and night to day power? If its an automated station, then why the wild variation?
Click to expand...

The time changes every month, and is specified on their license. It roughly corresponds to sunrise and sunset. Here are the Central Time zone times (as posted for WROK, Rockford, Illinois)

Monthly Local Sunrise Times
January 7:30
February 7:00
March 6:15
April 5:15
May 4:30
June 4:15
July 4:30
August 5:00
September 5:30
October 6:15
November 6:45
December 7:15


Monthly Local Sunset Times
January 4:45
February 5:30
March 6:00
April 6:30
May 7:15
June 7:30
July 7:30
August 7:00
September 6:15
October 5:15
November 4:30
December 4:30
 
Many Class D stations have authorization to use as much as 500 watts presunrise, and the power authorized for different time periods right after sunset in different months may exceed the lowest power nighttime authorization. So there may be more than one increase or decrease. This further complicates the analysis.
 
Makes sense it would follow the changing time as the seasons change, but this seems to vary almost enough that it's like someone is waking up late and suddenly realizing that the switch hasn't been thrown. ;D

Why more than one increase or decrease then? Is that because of the changing atmosphere as the sun begins to rise in the morning?
 
nocomradio said:
Makes sense it would follow the changing time as the seasons change, but this seems to vary almost enough that it's like someone is waking up late and suddenly realizing that the switch hasn't been thrown. ;D

Why more than one increase or decrease then? Is that because of the changing atmosphere as the sun begins to rise in the morning?
Click to expand...

As time went on, directional stations and daytime only stations found they were at a huge disadvantage, especially in certain months. Imagine going off the air every day at 4:45 in the afternoon right before Christmas! Or not being able to sign on until 7:30am, while everyone else across town is on at 6:00!

So to alleviate these issues, there were two rule changes- PSA (presunrise authority) and PSSA (post sunset authority). PSA let everyone kick it on at 6am at some reduced power level, then go to regular daytime power at the usual time. A station I worked for was daytime only, 1 kilowatt, with a PSA of 9 watts. It wasn't much but we were on the air and covred our little town.

PSSA is much the same, though it gives a graduated decrease in power. With it you might have 3 or 4 power changes before you go off teh air altogether.
 
 
That all makes more sense now!

I can see the disadvantage of having to sign off or on at those times from a business standpoint.

Thank you for all the responses and the helpful links too!
 
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