The Mystery of 108mHz
July 23, 2010 11:23 AM   Subscribe

When I was a teenager in the 1980's, I noticed that if I turned the radio dial on my FM radio all the way to the end, I picked up this weird transmission of repeating tones.

As far as I recall, it was there as long as my family lived in our house in Stafford County, Virginia. My sister said she thought it was a reminder so that you'd know you were at the end of the FM band. Her explanation did not make a lot of sense to me.

The transmission was difficult to describe but it was a high tone followed by a lower tone, with a reverb added so it made an echoing sound. Kind of a beedoo-doo-doo-doo..

I never did figure out what it was or where it was coming from. It's possible it was some kind of device installed inside our house, like the power management device the power company attached to the water heater, but it seems unlikely. There was a VOR radio navaid beacon for aircraft located a few miles away from us, but it was at 114.5mHz, and would have been transmitting the letters B R V in morse code. It's also worth considering that there were some secretive military radio listening posts not too far away, though it seems unlikely that they were transmitting in the FM broadcast band. (They were transmitting numbers stations in the shortwave bands but I did not discover that until the early 1990's.)

Any ideas what this could have been?
posted by smoothvirus to Technology (12 answers total) 8 users marked this as a favorite
 
Did it occur on both ends of the dial or just one? Broadcast television channel 6 audio sub-carrier used to be at 87.75Mhz.
posted by ChrisHartley at 11:32 AM on July 23, 2010


This immediately made me think of numbers stations (and reading about them in William Poundstone's "Big Secrets" as a wee lass).
posted by julthumbscrew at 11:33 AM on July 23, 2010 [4 favorites]


Oh sorry, didn't see your post title.
posted by ChrisHartley at 11:33 AM on July 23, 2010


I assume by 'end of the dial' you mean the high frequency end. Here's a chart of the allocation of the spectrum immediately past the FM radio frequencies. As you can see it's all aviation related.
posted by jedicus at 11:34 AM on July 23, 2010


Letter Beacon.
posted by Sticherbeast at 11:34 AM on July 23, 2010


ChrisHartley - just one end of the band, as I recall, right at 108mHz.

julthumbscrew - the interesting thing is that I know for a fact that there were numbers stations operating not too far from our house. But this wasn't a recording of repeating numbers, just the tones. As far as I know the numbers stations don't operate in the FM band.

Sticherbeast - interesting, but those are all broadcasting morse code, in the shortwave band, from Russia. Can't be it, this wasn't morse code, just a two tones together with some reverb.
posted by smoothvirus at 11:42 AM on July 23, 2010


Yep I thought that numbers stations were only on Shortwave, but there were polyphonic number station tones and some test signals. Here's one.
posted by multivalent at 11:46 AM on July 23, 2010


going from jedicus link, the radionavigation land test station seems like it could be a candidate. Apparently they were supposed to be on 108mHz. Also, the BRV VORTAC station was only a few miles away from my childhood home, and Quantico Marine Corps Air Station was not far away either.
posted by smoothvirus at 11:48 AM on July 23, 2010 [1 favorite]


I lived near an airport growing up and had the same experience. My money is on jedicus's explanation. I remember driving past an antenna that my dad described as being a navigation beacon. Looked like this:
http://www.freqofnature.com/aviation/images/vormzb.jpg
posted by cosmicbandito at 12:01 PM on July 23, 2010


You are almost certainly hearing the Morse identifier of a VORTAC, which start at 108.0 MHz.
posted by pjern at 2:27 PM on July 23, 2010 [1 favorite]


I'm with pjern. According to the Airnav database, there are no US VOR's operating at 108.0 MHz exactly, but the following US VOR's operate at 108.2:

NOGALES, AZ
OXNARD, CA
DENVER, CO
DURANGO, CO
HARTFORD, CT
LEWISTON, ID
BLOOMINGTON/NORMAL, IL
DODGE CITY, KS
ROBINSON, KS
MYSTIC, KY
SHREVEPORT, LA
WORCESTER, MA
BAD AXE, MI
NEWBERRY, MI
AUSTIN, MN
EVELETH, MN
BROKEN BOW, NE
LAS VEGAS, NV
WINNEMUCCA, NV
ALBANY, NY
GENESEO, NY
FINDLAY, OH
ROSEBURG, OR
SEVEN SPRINGS, PA
YARDLEY, PA
PROVIDENCE, RI
CHESTERFIELD, SC
FORT WORTH, TX
LLANO, TX
MIDLAND, TX
VERNAL, UT
ST CROIX, VI
NEWCASTLE, WY
posted by Dimpy at 6:54 PM on July 23, 2010


It appears that it could have been some kind of "test tone" signal coming from the Brooke VOR station. However it was definitely not morse code. The Brooke VOR broadcasts its morse code ident (BRV) on 114.5MHz.
posted by smoothvirus at 11:07 AM on July 26, 2010


« Older How do I sell a dead person's car in California?   |   Everyone is gifted, but some people never open... Newer »
This thread is closed to new comments.