# Section 3 - Technical Basics

## 3.10 Wavelength

Wavelength is the distance between two identical points on the wave, the length of one cycle. Consider ripples on a pond, if we were to look at a cross-section of these ripples they would be shaped like a sine wave. Their wavelength would be the distance between the peaks. Waves propagate out from an antenna in a similar way and travel through space. How convenient it would e if we could see and thus measure them! Wavelength is given the symbol , the Greek letter "lambda", and is measured in meters.

Lines A-A', B-B', and C-C' are all one wavelength long in the graph below. Observe that the graph is not only at the same level but is rising or falling at the same rate at both points chosen for the measurement of one cycle.

As wavelength increases, frequency decreases OR higher frequencies have shorter wavelengths. The graph below will allow us to convert wavelength to frequency or vice versa. Given a wavelength, look in a line across from that wavelength until it hits the line of the graph then look down in a line to the bottom and read off the frequency. Reverse the process to find a wavelength when given the frequency. For example a wavelength of 10m gives us a frequency of just under 30MHz and a frequency of 100MHz gives us a wavelength of just under 3m. You will be provided with this chart for your assessments.

When talking about frequency bands it is most common for radio amateurs to refer to them in terms of wavelength e.g. we say "the 20m band", not the "14MHz band", although both are correct, the use of wavelength is, by convention, more common.

## 3.9 Other Users

We share the radio spectrum with many other users. Each different group of users is allocated a different frequency segment or "band". In some instances other users may even share our bands, this is most notable on 70cm (430MHz) band where many low power devices such as alarm control fobs operate. Where a band is shared with other users this information is given in the band plans, and if you are asked any questions about band sharing in the assessments, then it will just be a case of interpreting a table provided to you by the assessor showing the frequency allocations. Look carefully for any overlap in these allocations showing shared use.

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