Frequency & Wavelength
The two equations that relate frequency and wavelength are:
Wavelength (in meters) = 300/Frequency (in MHz)
and
Frequency (in MHz) = 300/Wavelength (in meters)
The 300 comes from the speed of light, which is approximately 300 million meters/second. Frequency is usually expressed in terms of cycles/second or Hertz (Hz), and for most amateur use the frequencies have millions of cycles per second, so they are expressed as mega (millions) of Hertz.
As long as we’ve broached the subject, lets talk about scientific prefixes. While there is a longer, more complete list of these “multipliers”, these are the ones you’ll most likely encounter in amateur operations:
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These allow us a shorthand method of specifying a wide range of values without having to write numbers that either have a lot of zeroes after a decimal point, or after a number. Some examples are capacitors, whose values are often expressed as picofarads (pf) so that we have a 120 pf capacitor, instead of having to write 0.00000000012 farad, and a transmitter operating at 2.304 GHz instead of having to write 2304000000 Hertz.
Frequency bands based on decimal ratios of wavelength are often used to designate frequencies with similar behavior, some of the most common in ham use being:
| LF | Low Frequencies | 30 kHz - 300 kHz |
| MF | Medium Frequencies | 300 kHz - 3 MHz |
| HF | High Frequencies | 3 MHz - 30 MHz |
| VHF | Very High Frequencies | 30 MHz - 300 MHz |
| UHF | Ultra High Frequencies | 300 MHz - 3 GHz |
| SHF | Super High Frequencies | 3 GHz - 30 GHz |
Amateur operations are usually referenced to exact frequencies, or in another shorthand, a more generic wavelength “bands”. The value for the “band” referenced is usually rounded to a nearby integer value. Thus 14.301 MHz is in the amateur 20 meter band. The frequency allocations in each band in the U.S. vary by mode (digital/voice) and license class, and these limits are listed in Part 97. This is one of the things that drives most students crazy – all I can say, is try to memorize the limits that apply to the license class you are taking an exam for, remembering that the questions may not give you the precise value in the regulation, and realizing that you don’t need to get every question correct. Once you “get on the air” it is important to stay within the boundaries of your license, as failure to do so can result in fines or loss of your operating privileges. This is easy to do with modern equipment, as most of it comes with digital displays, and there are a number of sources of graphical representations of frequency sub-bands available online or in print (for example: http://www.arrl.org/FandES/field/regulations/Hambands_color.pdf ) which should be kept at your operating position for easy reference. Remember also, that all signals have some finite width, depending on mode, and setting your indicated transmit frequency at a band limit might result in generating signals outside of your operating privileges.
A quick list of frequency bands you might likely encounter.
| 160 meters: 1.8 MHz – 2.0 MHz |
| 80 meters: 3.5 MHz – 4.0 MHz |
| 40 meters: 7.0 MHz – 7.3 MHz |
| 30 meters: 10.1MHz – 10.15MHz |
| 20 meters: 14.0 MHz – 14.35 MHz |
| 17 meters: 18.068 MHz – 18.168MHz |
| 15 meters: 21.0 MHz – 21.45 MHz |
| 12 meters: 24.89 MHz – 24.99 MHz |
| 10 meters: 28.0 MHz – 29.7 MHz |
| 6 meters: 50.0 MHz – 54 MHz |
| 2 meters: 144 MHz – 148 MHz |
| 1 ¼ meters: 222 MHz – 225 MHz |
| 70 centimeters: 420 MHz – 450 MHz |
(In addition, there is the new (2003) 60 meter band, which is not really a band, but a set of five upper sideband (USB) only frequency assignments released by the NTIA. Amateur transmitters should be set to one of the following frequencies for operations in this band: 5.3305 MHz, 5.3465 MHz, 5.3665 MHz, 5.3715 MHz, and 5.4035 MHz. Occupied bandwidth is limited to 2.8 kHz and effective radiated power is limited to 50 W PEP)
NOTE: Over the years, the number of bands, and their frequency and mode limits, has varied. It is incumbent on the licensee to keep abreast of current regulations.
A band plan is a voluntary set of limitations, or gentleman’s agreement, as to where particular types of operations will take place within a band. Some band plans even vary from region to region. While these band plans do not have the legal restrictions of law, the FCC (as well as the regulators in other countries) looks to them when resolving disputes. At the very least, not abiding by these plans will earn you the wrath of your fellow operators, and a possible warning for not following the best amateur practices. The popularity of repeaters and satellite operations in the VHF and UHF bands have resulted in rather detailed band plans for these bands, along with volunteer regional coordinating committees that help ensure the best use of the bands. An example of such a band plan is the 2 meter plan for my area:
With the exception of the CW, SSB, and Satellite sub-bands, almost everything else is done as FM, or tone modulated FM for digital.
Simplex channels are “normal” – You transmit and receive on the same frequency.
On repeater channels, you listen on one frequency (the output of the repeater, or base station) and transmit on another (the one the repeater listens to). All other users do the same thing. In this 2 meter band plan, repeaters below 146 MHz use 20 kHz channel spacing, otherwise channels are spaced 15 kHz apart.
There are “standard” separations between transmit and receive channels for repeaters. The values are different for the various bands (Band-split: 29 MHz-100 kHz; 50 MHz-500 kHz; 144 MHz-600 kHz; 222 MHz-1.6 MHz; 440 MHz-5 MHz) On 440 MHz repeater inputs and outputs typically alternate.
