What's going on with my local AM station?
November 9, 2007 12:07 PM   Subscribe

Every since the daylight savings change last weekend, my favorite local AM talk station only comes in sporadically. What in the world could be going on?

I work in Ann Arbor, which is a city about 40 miles west of Detroit. My girlfriend lives in the city of Livonia, which is, more or less, about halfway between the two cities.

Over the summer, I started listening to a local sports talk radio station, 1130 AM WDFN (Detroit's The Fan), which broadcasts out of the Detroit-Metro area. Most commonly I listen to their afternoon talk show on my drive from work to my girlfriend's house - from about 5:00PM until 5:30PM - and I've never had any trouble.

Except something has happened that is very confusing to me. Now, I must preface this by saying that I have only in the last couple of days become really aware of this problem, so I have yet to really collect a satisfactory dataset.

On Monday, the day after the time change, I left work a little early (around 4:30), and drove out to my girlfriend's house, and had no trouble listening to the broadcast.

On Wednesday I had to stay late, so I left work at around 5:30. I noticed, much to my dismay, that I could not tune in the radio station at all. It was pure static. This has never happened before, and I thought it was odd, but I thought maybe they were doing some sort of tower maintenance or something and I just shrugged it off as an anomaly. I kept trying as I drove toward Livonia, and once I got relatively close, the station started to come in again. By the time I was in Livonia proper, it was back to working as per usual.

Yesterday, I left work at 5:00. The station was fine. I was driving toward the freeway, and at exactly 5:14 it was like someone flipped a switch and the station just cut out again. It was instantaneous - from crystal clear reception to absolutely nothing. I kept trying the station as I got closer to Livonia, and, again, as I got near the city the station started to come in again.

What the hell!

Why would this start happening all of a sudden? What's going on?

I have some theories.

First, I know there's the whole thing about how at night you can hear radio stations across the country because something, something, something, science, science, science something about radiowaves bouncing off the atmosphere.

Could this have something to do with it? I ask because I have only had this problem in the last week, and the only variable that has changed is the time - now when I leave work at 5:00-ish it's dusk, and by 6:00- 6:15 it's completely dark.

Another thing I noticed (just now) on the Wikipedia page for WDFN is this little note on their broadcasting power: "50,000 watts (Daytime), 10,000 watts (Nighttime)"

Could it be that at around 5:15 they're switching over to the less powerful "nighttime" broadcast mode, and the signal is simply no longer powerful enough to reach me out in Ann Arbor?

I know this is a weird question, and thanks for any help!
posted by kbanas to Technology (9 answers total) 2 users marked this as a favorite
Response by poster: As a follow-up, if it *does* have to do with the night change to 10,000 watts, why would a radio station lower their wattage so dramatically at night?

Is this a common practice?
posted by kbanas at 12:10 PM on November 9, 2007

AM radio signals can travel further at night than during the day, so the FCC requires some stations to reduce their wattage at night to prevent interference.
posted by L. Fitzgerald Sjoberg at 12:17 PM on November 9, 2007

Yes, they're reducing their power at night. This is required by the FCC so that your station will not interfere with distant stations. As you pointed out, you can hear distant stations, and your local stations can interfere with said distant stations, mainly at night, in the AM broadcast band. Yes, it's a common practice.
posted by JimN2TAW at 12:19 PM on November 9, 2007

Might also want to read this thread. (But it's fairly redundant to what's been said)
posted by one_bean at 12:23 PM on November 9, 2007

Response by poster: Stupid answering my own question.

Thanks for all the information!
posted by kbanas at 12:26 PM on November 9, 2007

Thanks for asking, though. That's a fascinating little nugget of information.
posted by empyrean at 12:42 PM on November 9, 2007

And of course "at night" has to do with RF propagation and therefore local sunset, not what the clocks say.
posted by Myself at 2:36 PM on November 9, 2007

It is so you are forced to listen to the right wing dribble of WJR, which broadcasts at about 1 million watts 24 hours a day...

And, you answered your own question... good for you!
posted by HuronBob at 4:51 PM on November 9, 2007

Just to add, in addition to reducing broadcast power, many stations are required to change the shape of their coverage as well. This is done through phasing a multi-antenna array.

We used to drop the power and activate the secondary antennas manually at the AM station I worked for in the late-70's. I'm assuming this sort of thing is automated these days.
posted by michswiss at 5:10 PM on November 9, 2007

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