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Two Way Radio for the 21st Century


Aerial Options

for MOTOTRBO Handportables

The aerial for a handheld radio will always be a compromise: too big and it gets in the way, the radio operator risks poking themselves in the eye, too small and the signal is attenuated too much - the working range of the radio is reduced.

The physical size of an aerial is directly proportional to the wavelength of its operating frequency. However at the VHF and UHF frequencies licenceable in the UK a standard aerial would be far too large to use with a handportable, so the favourite compromise is to use a quarter-wave aerial. This gives a reasonable balance between efficiency in radiation and size. It also has an omni-directional radiation pattern, just what is wanted to optimise the range of a moving handheld radio.

To calculate the size of the aerial we will need some physics and since we normally refer to a system's operating frequency, rather than it's wavelength, we use the imperial approximation:

     Length in feet = 234 / frequency in cycles per second. 

This gives us quarter-wave whip lengths at the typical band mobile transmits of 38", 16" and 6".

Whilst practical at UHF, these are still awkward at VHF; so we compromise again and wind the radiator into a spiral or helical shape. We loose some signal but gain a lot of practicality: 6" or less is sensible on a handportable. At UHF we have the choice of a straight whip - made out of multiple strands for flexibility - a multiwire aerial - or a smaller helically wound aerial. At VHF the helical is de rigeur.

VHF Helical Aerial

A VHF Helical aerial - about 6" long

VHF Condensed Helical Aerial

A VHF condensed helical (stubby) aerial - about 3" long

UHF Condensed Helical Aerial

A UHF condensed helical (stubby) aerial - about 3" long

Heliflex Aerial

A UHF helical aerial with integral GPS element - about 3.5" long

Multiwire Aerial

Multiwire Aerial

UHF Multiwire aerial - about 6.5" long