Sunrise, Sunset

We’re tearing another page off the calendar. Come Monday, it’s August. The days have been getting shorter for over a month now, a minute or two per day. For many AM radio stations, however, Monday will be quite a bit shorter than Sunday.

Certain AM stations are licensed to operate during the daytime only, defined by the approximate sunrise and sunset times in the middle of a given month. For this reason, operating hours will vary throughout the year. Take my company’s daytimer, WHIT. During June, the station signed on at 5:15AM and signed off at 8:45, its longest broadcast day of the year. This month, it gave back 15 minutes on each end of the day. Come Monday, sign-on moves up from 5:30 to 6AM, and sign-off moves back to 8:00 from 8:30. The broadcast day will continue to shorten as autumn and winter approach. In November, after the return of Standard Time, the station broadcasts from 6:45AM to 4:30PM. In December, sign-off stays at 4:30, but sign-on isn’t until 7:15AM. On January 1, however, the first sign of spring appears: although sign-on is delayed until 7:30AM, sign-off is a little bit later: 4:45PM. A station’s sign-on and sign-off times are a function of its latitude and longitude, so they can vary in different places.

Isn’t this variability a competitive disadvantage for radio stations? It can be. For most daytimers, however, variable hours are a simple fact of life you get used to—although I once worked at a company whose AM station signed on at 7AM and signed off at 4:45PM year round, even in the summer when they could have been on far longer, just because it was easier.

Some AM stations operate at night at reduced power. Power will be raised or lowered based on the same set of sunrise and sunset times. Often, a 5,000-watt station will cut back to 1,000, or something like that. The little AM station I worked for was authorized to operate at reduced power after sunset, but was licensed for three watts, or seven watts, or something similarly ridiculous—I forget. That wasn’t enough to get the signal from the transmitter, which was located just outside of town, back to the studios downtown, so we didn’t bother.

Other AM stations “go directional” at sunset. This means their signal propagates in a specific direction, to protect the signal of another station elsewhere in the country on the same frequency. In Madison, for example, WIBA-AM’s signal goes primarily north and east at sundown — you can be a few miles southwest of the tower after sunset and have trouble picking it up, where during the day you’d get it five-by-five. Reduced power or a pattern change is why you would sometimes lose your favorite AM station at sundown.

I was once in the wilds of Minnesota, cruising down a deserted interstate highway, listening to a big AM station out of Winnipeg, Manitoba, early on a winter morning. In the middle of a song, something odd happened. The station’s audio cut out for a second, then cut back in again, briefly distorted, before returning to normal. Then the morning jock keyed his microphone, mid-song, and said, “Good morning, western North America.” In an instant, I realized what I had heard: the morning pattern change. It was officially sunrise in Winnipeg, and it was no longer necessary for the station to propagate its signal eastward to protect some station out west.

I was pretty sure I might be the only person other than the jock who truly understood what had just happened.

The biggest AM stations operate 24/7 at full power, often 50,000 watts, which is as big as AM stations in the United States can be. These signals are called “clear channels.” If you surf around the AM dial late at night, the distant stations you receive will almost certainly be clear channels.

The clear channel designations and all this power-reducing and pattern-changing date back to the dawn of radio, when the Communications Act of 1934 standardized the “wild west” that the AM band had become in the 1920s, to limit interference and make sure local stations serve local areas effectively. The regulations are bureaucratic, but the reasons for them have everything to do with the laws of physics.

If I have made any technical errors in this post, I am certain that those amongst the readership with first-class FCC radiotelephone operator’s licenses will correct me, and thereby educate the whole class.

Read more about why AM stations have to reduce power at night here. And stop back Sunday for a first in the history of this blog: a rerun.

8 responses

  1. I could only pull in one station on my first radio (a Remco Tiny Tim crystal set) and found it odd that it signed off at sunset. The technical fascination grew when I noticed on the old living room Crosley console radio that the the very strong local top 40 station, WDGY, would suddenly transform itself into a fade-prone, 98-pound weakling at sundown. I couldn’t figure out why WDGY, less than ten miles distant and with 25,000 watts at night, came in so much worse than its crosstown competitor, KDWB, which ran a measly 500 watts nights from more twenty miles away. How could KDWB lose 90 percent of its power at sundown vs. WDGY’s 50 percent drop, yet not fall off the same cliff, reception-wise? And so a power/pattern change geek was born. I’d find myself scanning the dial at sunrise and sunset just to hear the changes/sign-ons/sign-offs.

    Because the majority of stations simply threw a switch, it was fun to hear those who would actually acknowledge their technical changes at sunset. I’d make it a point to tune in KWMT from my old hometown of Fort Dodge just to hear their “So Long ‘Til Tomorrow” sign-off jingle. The former KVOO/1170 in Tulsa once aired an announcement advising listeners to the northeast that they may not be able to hear the station after pattern change. Back in its top 40 days, Duluth’s 560 AM used to run a quick “WEBC now pauses for technical adjustment” blurb. They weren’t kidding: it was one l-o-n-g pause. Was the engineer out at the transmitter site using a broom handle to physically move the contactors in the phasor or something? For a number of years, a Minneapolis daytimer has used a produced bit that pokes fun at the antiquated notion of daytime-only radio stations, punctuated by a Jesse Ventura “this is an actual law” drop-in.

    Considering the long history of power and pattern changes, what puzzles me is some of the changes which have occurred since the FCC reclassified AM stations into classes A, B, C and D. The former class III “regional” channel stations used to have a maximum power limit of 5,000 watts, but since those channels are now class B, the upper limit has been raised to 50,000 watts. The first former “regional” station granted an upgrade under the newer regulations was Milwaukee’s WTMJ, which boosted power from a full-time 5,000 watts to 50kw days/10kw nights. On top of that, there are now a number of stations that *increase* power at night, like Wausau’s WSAU/550, which upgraded from 5,000 watts full-time to 15kw days/20kW nights. Granted, these upgraded stations have to use more elaborate directional arrays to theoretically reduce interference, but no matter how tight the new patterns may be, the nighttime signal level increases even in unintended directions. Add up the number of similar recent upgrades and nearly every former “regional” channel on the AM band now sounds like it has dozens of stations on it at night, much to the detriment of those stations that now find the increased nighttime “noise floor” harder to overcome in their own local service areas (and especially those class Ds who are restricted to less than 250 nighttime watts.) If AM stations have been forced to reduce power for all these years in the name of minimizing nighttime interference, what kind of sense does it make for the FCC to grant these sometimes substantial power increases? Yes, ambient electrical noise is a bigger problem than ever in urban areas, and some of these upgrades have been made to compensate for it. But the combined effects of all the increased wattage is making the AM band an even more garbled mess at night. No wonder so many AMs are looking for relief via FM translators.

    jb, which Winnipeg AM was it that you’d heard? Sounds like it might have been the former CKY/580.

    Gotta sign off now. It’s 9:00.

  2. I can remember listening to American Top 40 on an AM station out of New Orleans, and having it turn to static just as Casey got to Number Three. Pissed me right off.

  3. When I worked at WGLR back in the early ’80’s, it was an AM daytimer that always signed on at 6:00 am and signed off at sunset. During one bad snowstorm, my partner, who doubled as the station manager, and I signed on the station about 30 minutes late after walking behind a snow plow to get to work. We did the morning show together and I did the rest of the day myself. I think we signed off at about 4:30 pm. That was back when the station was actually located in Lancaster, WI.

  4. I didn’t see any mention of the locals at 1kW staying 1kW after sunset instead of .250kW, 1240, 1400 kHz and many other freqs. This happened in 1985 or so. I used to get 1240 AM in Albany at night but no more.

    1. BTW the FCC doesn’t give First Phones anymore, top one is 2nd Class w/some endoresement.

      1. Mikelj3: The reason you don’t see anything here about “locals at 1kW staying 1kW after sunset” is that I’m not an engineer, and 600 words on this topic strains the patience of non-geeks, let alone 800 or a thousand. And even if the FCC doesn’t give first phones anymore, there are in fact some first phones amongst the readership, because many of us are old.

        Dave: The Mrs. did afternoons at WGLR for a time. Her shift was 4:00 to sign-off, which meant that in the winter, she’d schlep 25 miles through a snowstorm to do a 30-minute shift.

        Yah Shure: It was indeed CKY, which was an oldies station at the time.

  5. […] had been powered down (jb at The Hits Just Keep On Comin’ provided a primer the other day on powering down and related topics), but KDWB was almost certainly my daytime choice. How is it, then, that I do […]

  6. Mikelj3, WJON/St, Cloud, MN, the “graveyard” channel station on 1240 where I once worked, discovered that – with the FCC’s blessing – they could effectively double the station’s nighttime power by replacing their original one-quarter wavelength (201′) tower with a more-efficient, five-eights wavelength (475′) structure. The taller tower would direct more of the signal at a lower angle toward the horizon, thereby strengthening the station’s ground wave and improving local coverage. Nighttime power would remain at 250 watts, but daytime output would have to be throttled back to about 481 watts in order to maintain the old tower’s 1kW daytime coverage.

    The only time I ever signed a station off the air occurred on a Saturday afternoon in July,1978, minutes before the old tower was brought down. When the new tower was completed a week later, I had the “honor” of powering down to 250W on that first night of improved coverage.

    It turned out that the increase in nighttime coverage was far more modest than management had hoped, since doubling an AM station’s power output does not correspond to a doubling in signal strength or coverage area (which would have required about a four-fold upgrade to 1kW.) But with the ungodly high nighttime noise floor on the six “graveyard” channels, even a very modest improvement had to be viewed as a plus, especially if it filled in some of the “dead spots” in town (and with St. Cloud sitting atop lots of granite, there were plenty.) Another plus: the broadbanded taller tower increased the station’s high frequency audio output, making the music programming sound great.

    The FCC okayed the blanket nighttime raise for graveyarders to 1kW (400W for those still running 100W) in 1983. In addressing the problem of nighttime noise on these channels, the FCC had considered the same approach that my old station had taken: the use of taller towers for nighttime improvement. But the commission realized that not all stations had the means or ability to erect taller sticks; hence the decision to raise power, instead.

    And – just as you discovered with your Albany 1240 station – the net result of that blanket power raise didn’t turn out quite like the FCC had envisioned it. instead, he combined effect of hundreds of 1kW stations sending double the amount of skywave from each of their towers resulted in an even more ungodly jumble of nighttime noise, to the point that many stations found their new 1kW nighttime coverage was less than what they’d had previously with 250W. Small town stations that depended on nighttime revenue from local sports play-by-play suddenly found their surrounding communites beyond their reach.

    Fast forward thirty-some years: for the first time in decades, I was in the St. Cloud area at night, and decided to check out WJON’s local coverage to hear the effects of that 1983 blanket 1kW nighttime power increase. Even with an increase to 481 watts, WJON’s signal in Clearwater, just ten miles distant, was much dicier than I ever remembered it when I worked there. So much for that expensive new tower’s advantage! But what about that high end broadband audio advantage? it wasn’t very apparent with an all-talk format. But I’ll tell ya, if you’re ever in St. Cloud as a thunderstorm approaches, park yourself under the WJON tower and watch a 475-foot insulated lightning rod in action. As the static charges build, electricity begins to arc over the insulators in unison down one set of guy wires, slowly at first, then with increasing speed until there is a lightning strike miles away. The process then begins anew. And to think how often I was on the opposite end of that electrical chain while wearing headphones…

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