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Thursday, April 18, 2024

We know about UHF and VHF; do they have Regular Frequency?

A STAFF REPORT FROM THE STRAIGHT DOPE SCIENCE ADVISORY BOARD

By  Straight Dope Staff
   
SHARE We know about UHF and VHF; do they have Regular Frequency?

Dear Straight Dope: Though it may now be irrelevant, I’ve always wondered: If PBS broadcasts (broadcasted?) on Ultra High Frequency TV channels, and the Big 3 networks on Very High Frequency, then what is, or where is (was?) just plain ol’ High Frequency, or Regular Frequency, or even Low Frequency? In other words, was this just 70s technical hyperbole, or word inflation? What’s the straight dope? Miriam Erez

Ian replies:

Hey, PBS was on channel 5 where I came from, but I still see what you mean. The problem is not so much exaggeration as a lack of ways to name ever-higher rungs on the ladder. And, ’twasn’t 70’s hyperbole, but ’30’s. In 1932, the International Telecommunications Union didn’t really know the difference between Kermit and Bart Simpson, they just knew that they had to decide where in the frequency band to place transmissions of varying types. There were 9 band numbers allocated by the commission, each band with a frequency 10 times as high as the previous one.

Band 4 (yeah, I know, they started with 4), Very Low Frequency, is from 3-30 kilohertz, Band 5, Low frequency, is 30-300 kHz, and Band 6, Medium Frequency, is from 300 kHz to 3 megahertz. In these three bands, up to 540 kHz we have radio navigation, and maritime and aeronautical use. From 540-1605 kHz is the bandwidth reserved for AM radio, and the rest of Band 6 is some amateur radio, more navigation, and radio astronomy stuff.

Band 7 is High Frequency, from 3-30 MHz, mostly just jumbled stuff as far as the masses are concerned, including amateur, international, business, and military use. Band 8 is Very High Frequency, from 30-300 MHz. VHF, pre-cable readers undoubtedly recognize, is where all the cool stuff is. From 54-88 MHz, we get channels 2 to 6. In between channels 6 and 7, from 88-174 MHz, we get our FM radio broadcasting, along with other amateur and comm frequencies. Obviously, VHF TV hogs a lot more bandwidth (6 MHz per channel) than radio (200 kHz for FM, and a meager 20 kHz for AM). TV channels 7-13 lie between 174 and 216 MHz.

You just kind of run out of ways to say “increasingly greater,” so here’s where the superlatives start: Band 9 is Ultra High frequency (300-3,000 MHz), and carries not only grainy TV signals, but public safety communications, forestry, highway maintenance, cellular telephones, and your obligatory amateur and other assorted comm uses. Band 10 is called Super High Frequency (microwave), and Band 11 is Extremely High Frequency, each 10 times higher in frequency than the one before. Up here, we have satellite downlinks and police radar. Above that, the frequencies are unassigned, and they include infrared, visible light, UV rays, X-rays, and gamma rays as you go up the scale. Below the assigned frequencies, you have Extremely Low Frequency from 30-300 hertz, used mainly for submarine communication, and the frequency from 300-3000 Hz, which was thankfully declared unsuitable for long-distance broadcast, except when you shout really loud.

Ian

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