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Band / MHz Relationships

Discussion in 'General Technical Questions and Answers' started by DIK909, Oct 9, 2017.

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  1. DIK909

    DIK909 QRZ Member

    Greetings, all. :)

    I am relatively new to Amateur Radio, and am currently studying for my Technician/General license(s). It's one thing to simply memorize the correct answers, which I've been doing, but I want to fully understand what I'm memorizing.

    Thusly: What exactly is the relationship between bands and Megahertz ? One is wavelength, and the other is cycles, yes ? Cycles of what ? Cycles = frequency ? Frequency of what ? How do hertz frequency cycles "fit into" wavelength bands ?

    If you can offer any resources or clarification on this, I would be most appreciative.

    All the best,
    JD
     
  2. WA7PRC

    WA7PRC Ham Member QRZ Page

    The "frequency" refers to the repeating alternating current waveform. Wavelength and frequency have an inverse relationship... the higher the frequency, the shorter the wavelength and vice versa. In free space...

    Wavelength (meters) = 300 / FMHz
    Wavelength (feet) = 984/ FMHz

    From http://en.wikipedia.org/wiki/Wavelength:

    "In linear media, any wave pattern can be described in terms of the independent propagation of sinusoidal components. The wavelength λ of a sinusoidal waveform traveling at constant speed v is given by
    [​IMG]

    where v is called the phase speed (magnitude of the phase velocity) of the wave and f is the wave's frequency. In a dispersive medium, the phase speed itself depends upon the frequency of the wave, making the relationship between wavelength and frequency nonlinear.

    In the case of electromagnetic radiation—such as light—in free space, the phase speed is the speed of light, about 3×10^8 m/s. Thus the wavelength of a 100 MHz electromagnetic (radio) wave is about: 3×10^8 m/s divided by 10^8 Hz = 3 metres. The wavelength of visible light ranges from deep red, roughly 700 nm, to violet, roughly 400 nm (for other examples, see electromagnetic spectrum)."
    Velocity (v) is determined largely by the medium. In space, it is very nearly the speed of light, (C) with a velocity factor of 1. Anything added slows it down, with a velocity factor less than 1.
     
  3. SM0AOM

    SM0AOM Ham Member QRZ Page

    The band designations have historical backgrounds, and are originally derived from the "Hoover Bands" of 1924 vintage, which predated international regulations. Here, the band centres happened to coincide with a rounded off number of wavelengths expressed in meter.

    "200 meters and down" 1650 - 2000 kHz (centre = 1875 kHz or 160 m)
    "80 meters" 3500 - 4000 kHz (centre = 3750 kHz or 80 m)
    "40 meters" 7000 - 8000 kHz (centre = 7500 kHz or 40 m)
    "20 meters" 14000 - 16000 kHz (centre = 15000 kHz or 20 m)

    It was common practice to express spectrum limits in "meter wavelength" instead of frequency in cycles/second or Hz in the 1920's.
    Not until the 1932 Madrid ITU Radio Regulations were official limits expressed in frequencies

    Even with the subsequent narrowing down of the amateur radio bands by the 1927 Washington ITU Conference,
    and the addition of more bands such as "10 meters" and "15 meters" (21000 - 21450 kHz) at the 1947 Atlantic City ITU Conference,
    the designations stuck, even if for example "15 meters" is actually 14,285 to 13,986 meters
    (and was originally called the "14 meter band" especially in German literature).

    73/
    Karl-Arne
    SM0AOM
     
    N2EY likes this.
  4. W5DXP

    W5DXP Ham Member QRZ Page

    I've noticed that when someone talks about the "higher bands", sometimes they mean the "higher frequency bands" and at other times they mean the "higher wavelength bands".
     
    WB5YUZ and WA7PRC like this.
  5. SM0AOM

    SM0AOM Ham Member QRZ Page

    The ages-old designation of "Top Band" for 160 meters is a good example of this confusion...
    Even the very first 1912 regulation of "200 meters and down" actually meant "up" in frequency.

    73/
    Karl-Arne
    SM0AOM
     
    WA7PRC likes this.
  6. W1VT

    W1VT Ham Member QRZ Page

    If your search the QST archives you can find early references to the 14 meter band.
    But, that leads to confusion with the 14MHz band, so it is more practical to call the 21MHz band 15 meters.

    Zack W1VT
     
  7. SM0AOM

    SM0AOM Ham Member QRZ Page

    Yes, it seems reasonable.

    I read all the 40's and 50's QST volumes while in grammar school during the early 70's, but this evolution slipped my attention.

    In more recent times, I got the German books "Der Kurzwellenamateur" and "Senderbaubuch" from the early-50's, where this new band was referred to as 14 meters. It also appears that this custom was quite quickly abandoned even here in Europe.

    For what I can remember, Swedish literature referred to 21 MHz as 15 meters from the beginning, except when German texts had been translated.

    73/
    Karl-Arne
    SM0AOM
     
  8. W0IS

    W0IS Ham Member QRZ Page

    Wavelength in meters times frequency in megahertz equals 300. For many of the ham bands, this is only approximate, but for the multiple choice test, it's close enough. For example, the 3.5 MHz band is 80 meters. 3.5 x 80 = 280, which is approximately 300.

    This fact will allow you to answer many other questions. For example, the test will ask you the length of a quarter-wave vertical for 144 MHz, or it might ask you the name of the 144 MHz band. 300/144= 2.083. "2.083 meter band" isn't one of the answers, so you go with the closest one, which is "2 meter band". The length of a "quarter wave" antenna for that frequency would be about 0.5 meters long. If you know that a meter is about 3 feet long, then you know that the antenna is 18 inches. The closest answer on the test is 19 inches, so that must be the right answer.
     
  9. N2UHC

    N2UHC Ham Member QRZ Page

    I have a feeling that we wouldn't even care about meter bands had they not initially tuned using wavelengths rather than frequency back when radio was in its infancy.
     
    K0OKS likes this.
  10. K9STH

    K9STH Ham Member QRZ Page

    There was an article in Radio Broadcast Magazine, almost exactly 90-years ago, in the November 1927 issue, about this very subject!

    Attached is a scan of this article. Since the scan is actually a scan of a scan, it is a little hard to read. But, the subject is definitely interesting.

    meter=kHz-1.jpeg

    Glen, K9STH
     
    N2UHC, WB5YUZ, N2EY and 1 other person like this.

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