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29 July 2008

AM Radio

Old passions have been stirring within me...

As a boy, I had a great interest in radio. It fascinated me that five dollars in parts allowed me to pick up signals originating half-way across the world. By the time I was 13 I had made quite a few receievers and even a few simple transmitters. For the longest time I ignored the AM and FM radios that were all around me, preferring to search out exotic shortwave broadcasts and far-slung CB and ham radio operators.

On a family road trip, my father turned the radio on to AM and tuned in station KOA which originates out of Denver, Colorado. It was late at night and we were in the western U.S., somewhere between central Texas and Montana--I don't remember where exactly. But the point is that were were a long ways away from Denver. I asked Dad how we could pick up such a far away station and he explained that a few stations had extra powerful signals that could be picked up from great distances. I thought that was cool.

Later on at home I tried to tune in KOA without success. At first I was puzzled. It took time and research to figure out how things worked. By rule, KOA and other stations like it must wait until sunset to turn up the juice to 50,000 watts. By that time the local and regional stations using a frequency (AM 850 in the case of KOA) are off the air. This rule was created by the FCC in the early days of radio before there were a lot of broadcasters. The argument was that rural listeners with no local radio station would benefit from the signal pumped out by these far-away big stations. These stations are known as clear channel stations (not to be confused with Clear Channel Communications).

Radio manufacturers took advantage of this. My father has an antique radio. Manufactured by Packard Bell (not the same company that made computers in the 1990's), I'd say it was made in the early 1950's. The neat thing about it is that the tuner is divided into two halves. One side, labeled "northwest" contains the call signs of the regional clear channel stations stacked above the numeric frequencies. The other side, labled "southwest" is marked the same, except with different stations. Is suspect there is a corresponding layout marked for "northeast" and "southeast" that was marketed in those regions as well.

If you're bored one night, and you have an AM radio nearby, I suggest you give it a try. It is fun to see which is the furthest station you can tune in. (Note: you'll get a better signal if you tune in close to an equinox.) The Internet is full of sites that will give you helpful pointers.

I wonder how much tubes are going for on eBay these days...