Tuesday, July 19, 2016

I have a question about the term ‘meter’ as it relates to the various labels used for amateur bands..

Q John asks, “I’ve just started studying for my Technician license and I have a question about the term ‘meter’ as it relates to the various labels used for amateur bands. Does the ‘meter’ of a given band correspond to the wavelength of the frequency of that band?”

Not necessarily. When you’re discussing Amateur Radio frequency bands, consider their metric labels in broad terms only. This will be easier to understand once you know the historical background. However, let’s start by defining a “meter” in terms of wavelength.

To convert wavelength to frequency, the speed of light is used, as it is also the speed of radio waves. In metric, this is 300 million meters per second. So the conversion formula is:
F(MHz) = 300/wavelength

wavelength = 300/F(MHz)

So, 6 meters is really 50 MHz; 2 meters is actually 150 MHz and 70 centimeters (0.7 meters) is 428 MHz. Notice that the frequency that corresponds to 2 meters is well above what hams consider to be “2 meters.”

While some folks would like to have the bands named more accurately (2 meters would be 2.1 meters, for example), tradition
runs deep in this hobby and the majority feel this tradition should be preserved.

In this day of computer-controlled rigs, it is easy to forget that radio technology was once crude indeed. Before the advent of vacuum tubes, there was no such thing as an amplifying oscillator with feedback to control it. Radio signals were generated via a spark gap.

Anyone who has listened to an AM broadcast radio when a thunderstorm is approaching knows that sparks generate wideband RF. The lightning discharges will create bursts of RF that cover the entire AM band. Thus it was in the early days of radio—transmissions were made by spark and the best one could do to limit the output bandwidth was to use an output filter made of a couple of inductors and capacitors along with a narrow-bandwidth antenna. This determined what “band” you were on and you could hear everyone else on the same band at the same time.

Yes, it was bedlam after a fashion, but the range you could work was quite short (a couple hundred miles was “DX”) and there were far fewer operators then. The label for a particular band was broadly interpreted because the signals themselves were broad—and that legacy remains today. That’s why we have a “20-meter band” at 14 MHz even though the true frequency equivalent of 20 meters is 15 MHz!

From QST June 2001