Aerial (Antenna) for Handheld Radios
About Stubby, Helicals and other Walkie-Talkie antennae.
This article has been written to be as non-technical as possible without loosing the key concepts. If you are a physicist or a radio amateur apologies for any simplifications.
Aerials size, shape and effectiveness is totally governed by the laws of physics and is relative to the frequency it is designed for. Higher frequencies typically require shorter/ smaller aerials which is why your VHF (88-108Mhz) car radio may have an aerial up to 1m long but your mobile phone (800-1.2Ghz) has an aerial small enough to be inside the phone. There is no magic aerial design better than any another. Aerial design and choice is a trade-off between efficiency, directionality and size: Explained below.
Since it is the aerial which is the element that both collects the received signal and radiates the transmitted signal then the correct type of aerial for the particular application will help with improving range.
Aerials broadly fall into two types.
- Omni-directional -Which radiates more or less equally in ALL directions (three planes). this called a
- Dipole Directional - Which radiates in one particular direction or plane more than another. This type of aerial is said to have 'Gain' in a particular direction in comparison to an Omni-directional aerial.
Note: Above I have mentioned 'Radiating' which implies transmitting but almost always receive sensitivity equally has gain in the same direction as transmit.
Note: Aerials or Antenna do not have Gain in the sense that they amplify a signal. They are purely passive and the word Gain refers to directionality in comparison to a true omni-directional antenna. In other words if an aerial has Gain it will pick up or radiate in one direction better at the expense of other directions.
Directional aerials (antenna) like a TV aerial have high gain in one direction (which is why all the TV aerials in your area are pointing in the same direction i.e. at the nearest TV transmitter. They are also quite large. An Omni directional TV aerial would only be about 10cm long but since your house and the TV transmitter are fixed then the aerial has to only ever collect signal from one direction.
A directional aerial is of course not much use when either transmitter or receiver are moving around and may be in any direction..such as in typically hand-held radio use. For a walkie-talkie or vehicle mobile radio you need an Omni-directional aerial....sort of....
..we live on a fairly flat earth, at least as far as us earthlings can see it is. When we talk on our two-way radio we are talking to another earthling on the same plane. Power transmitted from our radios vertically skyward is wasted so an ideal aerial would radiate horizontally in all directions and less so skyward (or downward).
The 1/4 wave Whip: The ideal aerial for a Hand-held radio.
So we have established we need to radiate horizontally in all directions. The simplest design of aerial is ideal for this. It is called the 1/4 wave dipole (aka 1/4wave whip) and consists of a length of wire (conductor) 1/4 of the wavelength of the frequency we are using.
VHF radios around 160Mhz have a 1/4 wave of around 45cm
UHF radios around 449Mhz have a 1/4 wave of around 16cm.
These lengths are what makes up as near to an ideal hand-held radio antenna as the laws of physics allow and these are the sizes of antenna that you should be using if you want best range from a hand-held.
The problem for VHF radio users is a 45cm antenna is rather unwieldy. To get around this aerial makers wind the aerial into a Spring or Helical.
Helical Aerial (Stubby): Not so efficient but shorter:
The helical aerial is shorter and more practical for some users but it is not so efficient a radiator or as sensitive as a 1/4wave whip. It is however the only practical antenna of most hand-held VHF radios.
Stubby Helical: Even shorter, even less efficient.
Even a VHF helical is quite long at 15-20cm so Stubby Helical are also available which are even less efficient. These should only be used where range is never an issue.
Summary of Antenna Choice:
1/4wave whips are ideal but unwhieldy and many radios are not built to withstand the extra stress that such a long aerial places on the radio body.
VHF helical (the long ones) are the best allround option.
VHF Stubby Helicals are only suitable where range is never an issue.
External VHF Dipole (Rucksack aerials):
Some Search and Rescue users like to connect an external rucksack carried Dipole aerial by cable to their radios. These will generally give better range than a radio mounted aerial. This improvement can be marginal as moving a few meters uphill will often give the same or better improvements.
The big weakness of Rucksack aerials is that there are several points of potential wear and weakness: Cable, connectors and the long dipole. They usually need to be used along with a Speaker Mic (RSM) which has its own cable and connectors so frequent close inspection of all these extra parts for damage is required.
1/4wave whips are ideal and should be the only choice where maximum range is required.
Helical / Stubby aerials are also available and should only be used where range is not an issue.
Antenna Types used in Radio communications.
1.4 wave whip: Omni directional in the horizontal plane. Losses in the vertical plane. So some gain relative to a dipole. Efficient transfer of signal to the radio.
Typically used on hand-helds and vehicle radios. An ideal solution.
Helical: Omni directional in the horizontal plane. Losses in the vertical plane. Some losses in transfer of signal to the radio. Negative gain (losses) relative to a dipole.
Typically used on hand-helds only.
Yagi. Highly directional in the horizontal and vertical plane. Very high gain but very directional relative to a Dipole.
Typically used only for point-to-point applications.
Co-linear. Omni directional in the horizontal plane. High losses in the vertical plane. So typically modest or high gain relative to a dipole. Efficient transfer of signal to the radio.
Typically used only for base-station and repeater antenna.
Base Loaded Whip: Omni directional in the horizontal plane. Losses in the vertical plane. Modest gain relative to a dipole. Efficient transfer of signal to the radio.
Typically used only on vehicle VHF radios.