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I understand the conversion between meters and Hz, kHz, MHz, etc. but I don't understand why ham operators frequently switch between using one or the other.

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The radio typically uses frequency, and if you are talking about a specific location on the dial, that's typically more accurate. For instance, 442.125 might be a specific repeater. But to convert that into 67.85412cm would be nearly meaningless (the radio won't take that), and it's a lot of digits with questionable accuracy.

But if you are talking about the band, saying 430-448MHz is not very fun, it's much easier to say 70cm band even though (or especially because) that's kinda rounded and not very accurate.

Also, sometimes the wavelength is more interesting. When you say "2m antenna", I know it's going to be a half wave or quarter wave, and so be around 1m or 0.5m (depending on antenna type).

And hey, this is a technical hobby. You can convert those numbers in your head anyway, right? :) (Or you will be able to if you use them enough.)

On the flip side, it does get confusing with the lack of consistency. Did you mean 10m band or 10MHz band? 17m or 17MHz? (oh wait, that's the same band!)

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    $\begingroup$ Thanks, OK so the reason to use hertz is clear. Regarding wavelength, could you clarify the point about the "2m antenna" telling us that the antenna will be 0.5m or 1m and quarter or half wavelength? That would be very helpful to understand. Not all waves have the same wavelength, so does the "2m" here mean it is optimized for wavelengths of 2m, which corresponds to the 2m radio bands? And are you saying that the physical height of the antenna will therefore be either 0.5m or 1m tall or long, presumably because the antennas at those ratios for some reason I probably learned then forgot? $\endgroup$
    – Hack-R
    Sep 11, 2022 at 18:33
  • $\begingroup$ Regarding the part about the imprecision, e.g. "430-448MHz" vs. "70cm" I get what you're saying, but I'm not sure I consider it an entirely "valid" reason (not that you need my approval!). Wouldn't it be just as easy to use an approximate midpoint in hertz as in wavelength? So a fair comparison would be calling it the "440MHz band" vs. the "70cm band" in my humble opinion. $\endgroup$
    – Hack-R
    Sep 11, 2022 at 18:41
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    $\begingroup$ 70cm vs 440MHz: agree, there's not a lot of reason to pick wavelength there. But both approaches are correct, so there's not a lot of reason not to either. As to "not all waves have the same wavelength..." but all waves of a particular frequency do have the same wavelength, so what's your point? $\endgroup$
    – user10489
    Sep 11, 2022 at 20:40
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    $\begingroup$ Dipoles are very close to a half wavelength. Monopoles are really half dipoles with the other half borrowed from a near by object, so they are a quarter wavelength. These are features that make them resonant at a particular frequency (or range of frequencies). That's a whole question to itself. $\endgroup$
    – user10489
    Sep 11, 2022 at 20:43
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    $\begingroup$ Sounds right. Note however, that the "80m" band is sometimes called the "75m" band depending on which end you are using, so it sometimes get squishy when things are rounded. $\endgroup$
    – user10489
    Sep 11, 2022 at 21:03
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To transmit you usually need at least 2 things, something that oscillates, and an antenna. The operating frequency of the oscillator or resonant circuits are usually calculated, measured, and/or displayed in cycles per something or Hertz. But even before controlled oscillators were used, radio waves were sent by antennas, where the frequency was set partially or mostly by the length or size of the antenna, and how that related to the wavelength of the signal to be sent. Today people often used stubby antennas, but efficient ones are closely related to some simple rational fraction of the wavelength being used (half being a common one). When the amateur bands were set, those lengths were rounded to a set of easy big numbers.

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  • $\begingroup$ Thanks. This is helpful info, but I could use 2 clarifications. Could you clarify this part (I think there may be a typo): "and how that related to the wavelength of the signal to be sent." Also, regarding "controlled oscillators", what does it do exactly - is this what determines the wavelength being generated based on the voltage? $\endgroup$
    – Hack-R
    Sep 12, 2022 at 16:07
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    $\begingroup$ The RF signals sent by spark transmitters often depended on the resonance of the antenna system, so frequency was determined by size (Hz by meters), but there was no cheap way to measure the resulting frequency precisely. Later, more affordable instruments and active circuits were developed that could more closely measure and generate specific RF frequencies, allowing control over the Tx wavelength from the transmitter in Hz. Usually something to do with varying capacitance or inductance somewhere in a circuit inside a box. $\endgroup$
    – hotpaw2
    Sep 12, 2022 at 16:37

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