Why am I picking up AM stations in NYC and Boston on my car radio?

November 5, 2013 5:25 PM

I live about an hour west of Toronto yet instead of getting CFRB 1010 from Toronto, I'm getting 1010 WINS out of New York City (albeit not terribly clear). I also can pick up WBZ 1030 from Boston and the signal is crystal clear, particularly in the evenings. I would think that since I'm in close proximity to Toronto, I'd pick up AM sations from there. CFRB 1010 does come in sometimes but not consistently. What gives? My car is a Mini Cooper S if it matters.
posted by Babushka to Grab Bag (10 answers total)

They are "clear channel" stations, not to be confused with Clear Channel stations.
posted by briank at 5:29 PM on November 5, 2013 [2 favorites]

Skip
posted by bondcliff at 5:35 PM on November 5, 2013 [5 favorites]

WBZ's transmitter is something like 50,000 watts. I remember listening to Larry Glick at night as a kid, and he had callers from people as far west as the Rockies who could pick up the station.
posted by mon-ma-tron at 6:13 PM on November 5, 2013

This recent article about KMOX in St. Louis (and Cardinals baseball) shed a lot of light on AM transmission stuff for me. (Sorry -- NYT paywall.)
posted by pantarei70 at 6:26 PM on November 5, 2013 [3 favorites]

It's most likely just after sunset and just before sunrise for science reasons. I once got Chicago 670 AM clear as a bell while driving next to DC National Airport. It's kind of fun to skip through the AM channels around these times and see what can be heard. (Even the static is fascinating, because it is just a humdrum of all the signals on that channel. You can hear snippets of words as the different signals compete with each other.)

In an age before the internet, this was really, really cool. "Holy shit, it's John Records Landecker on WLS!" "Oh my god, I'm getting KFI in St. Louis!"

Another thing that happens is that AM radio stations have to turn down their transmitters to night power at sunset. Sometimes they forget. Huge FCC violation, but if nobody complains, no harm no foul.

Back in the good old days, there would be giant AM transmitters on the Mexican border that they would keep at ridiculous power settings all night long. Like 50,000 , 100,000 or even 250,000 watts. The classic rock and roll DJs like Wolfman Jack would record a show in the afternoon and send a driver with the tape to the transmitter to play it back at night. The signal would practically saturate the continent.
posted by gjc at 6:42 PM on November 5, 2013 [2 favorites]

Addendum: AM (amplitude modulation) radio is a dead simple protocol. Signals coming into the receiver at the same frequency just add to each other. That's why you can hear really odd buzzing and phasing noises on the AM dial. Your radio has no way of discriminating between a near and a far channel. This is different from FM (frequency modulation), where the tuners have the ability to lock onto one carrier or another. (On the other hand, this is why FM stations in fringe areas will go back and forth between mono and stereo, and sometimes between two different stations at seemingly the same loudness. The tuner can only lock onto the "loudest" signal, and if the signals alternate, the tuner gets confused.)
posted by gjc at 6:54 PM on November 5, 2013

Aw, great memories for me here. My dad and I used to listen for skips. He told me that the time of day affected the radio waves and how far they could go. I think that before and after the Internet age this is cool!
posted by chainsofreedom at 7:11 PM on November 5, 2013

It's caused by Atmospheric Ducting. The Tropospheric Ducting Forecast can help you understand when it might happen again.
posted by Confess, Fletch at 7:44 PM on November 5, 2013

As a kid in Seattle with a shortwave radio, i got stations from the Caribbean, Russia, and Australia. The technology is basically the same as AM radio.
posted by miyabo at 5:07 AM on November 6, 2013

In an age before the internet, this was really, really cool.

It's still pretty fucking cool.
posted by downing street memo at 9:01 AM on November 6, 2013