Setting up an Amateur Radio Station Includes:
How to set up amateur radio shack Buying best HF gear Buying best VHF/UHF equipment Linear amplifier How to buy kits Buying used equipment - a guide Choosing & buying the best antenna
Possibly one of the most difficult choices for any amateur radio station is the choice of the antenna..There is always a good discussion to be had on what types of antenna perform the best under given circumstances. For some the choice may be a large directive antenna on a high tower, but for most radio amateurs space and many other restrictions mean that compromises have to be made.
When there are restrictions the challenge is to adopt the best form of antenna for the particular location. This can often lead to some experimentation which is normally very interesting and leads to a much better understanding of the operation of antenna systems.
There are many options for antennas that can be taken, some simple, some that can be made, some that are bought . . but whatever type of antenna is chosen, it will be interesting to see the results. Some of the very many options for antennas are given below.
End fed wire antenna
The end fed wire, often called a longwire antenna is one of the simplest to build and install. Simply it consists of a length of wire that is connected to the receiver or transmitter.
Often this type of antenna is called a longwire antenna, although a true longwire antenna is many wavelengths long, rather than a random length, often only less than a wavelength.
One of the simplest and most cost effective antennas is the dipole. If mounted as high as possible it can perform well. As the length of the dipole determines its frequency of operation, these antennas are normally only used for a single band, although there are versions that can be used for HF multi-band operation.
On occasions a dipole may be used at VHF, especially for 6 metres, although often they are the driven element for a directive antenna such as a Yagi.
Dipoles are straightforward in their design and hence they are quite easy to make. Often wire cut to length for the frequency of operation and fed at the centre.
HF wire doublet
The doublet is actually a form of dipole, but using an open wire feeder and an antenna matching / tuning unit, it can be used on a variety of bands. The drawback for the doublet is the open wire feeder which cannot easily be run though a house without becoming unbalanced.
The doublet antenna is normally used for the HF bands, where typically the lowest frequency of operation is where the antenna forms a half wavelength.
The vertical antenna is ideal in many situations. Being vertical, the maximum radiation is parallel to the earth’s surface in an ideal world, and in reality it has a lower angle of radiation than a horizontal dipole under most circumstances. It also has omnidirectional radiation pattern in the horizontal plane enabling all-round radiation and it does not need to be orientated to receive signals from different directions. This can be an advantage at HF and also VHF / UHF.
For HF it occupies much less space than, for example a dipole, and therefore it can fit into many small garden plots. It can be run against a proper ground, or elevated using a radials acting as a ground plane. This gets the vertical higher and enables it to have a much clearer take-off.
For VHF / UHF vertical antennas are widely used for FM operation. As many stations using FM are mobile, the omnidirectional radiation pattern means that antennas do not need to be re-orientated as the vehicle moves. Accordingly vertically polarised antennas are standard for FM at VHF and UHF.
Directional antennas - Yagi
Many stations require additional gain over dipoles and vertical antennas and antennas like the Yagi are common, both at HF and they are almost exclusively used for longer distance operation at VHF and UHF.
For HF operation a tower is often required, and accordingly a reasonable sized plot of land is needed. Planning permission is also needed in many countries.For VHF and UHF the antennas are more manageable and can often be mounted on fixings attached to the house, although large tower may still be used where space permits.
More Ham Radio Topics:
What is ham radio Callsigns Morse code Voice modes Digital data modes Digital data modes QRP operating Codes & abbreviations Ham bands overview Operating via differnet propagation modes Repeaters Callsigns Contact formats Setting up a shack & buying the right equipment
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