TWO-WAY
RADIO CONSIDERATIONS FOR 4X4 DRIVERS
By Eric Skeen (aka Family_dog)
I would like to present an “easy to follow”
article on Two-Way Radios and Licensing procedure. In a short article
such as this, one cannot present all, but hopefully enough to help
clear some confusion.
Some of this article has been culled from previous
articles, I will try weed out the repetition as I go along.
WHAT TYPE, 29MHz AM or FM?
29MHz
AM RADIOS
The virtues of 29MHz AM radios are many – they are relatively
cheap and many Clubs and 4x4 drivers make use of them. They are
priced at around R800 – R1100 excluding antenna & installation.
Their reliable operating range is anything from about three to fifteen
KM or thereabouts, but this varies greatly with weather conditions
and time of day, as well as area of operation and motor vehicle
suppression..
Pros:
Relatively cheap; fairly popular and in common use by many Clubs
& Organisations. Licences quick & easy to obtain.
Cons: Very few Manufacturers of these units as it is no longer considered
a serious Commercial product. Reception is hampered by poor weather
conditions and electrical impulse noise, particularly with petrol
engines.
Antenna
location is important with AM, a permanent mount is to be preferred
over a magnetic mount, and ideally the antenna should be mounted
in the middle of a large expanse of metal, such as the roof of a
double-cab. This might not always be convenient, and mounting the
antenna elsewhere could result in directional RF radiation. Usually,
you could always expect up to 5Km useful coverage between two
like units.
Photo of Dragon KR-80 AM Radio
FM RADIOS
The
most common FM radios operate on VHF, which is a range of frequencies
within the 146-174MHz band. FM radios offer very good distances,
anywhere from about 25-50Km between mobile units but once again
dependent upon terrain! They are powered at 25W RF and are relatively
immune to interference caused by atmospheric or electrical conditions.
The radios are not freely available over the counter however, because
of stringent ICASA licensing requirements. Upon receiving a Licence,
you will not be granted a country-wide frequency, but one for your
own private use and it will not necessarily be the same as that
in use by any Club or other user. In fact, other than joining the
local chapter of a 4x4 Club and making use of their allocated frequency,
you might consider getting together with some local pals and forming
your own 4x4 club, writing a constitution, and obtaining a licence
in the name of your new club. More on this later.
An
advantage of a multi-channel FM radio is the ability to operate
on your Business Frequency, should you so desire, as well as the
"recreational" frequency. Therefore, the Taxman should
pay for your radio if you have a Business application for it as
well
.
Pros: Extended range, high-power RF, clear reception,
modern communication tool
Cons: Price varies from R1800-R2000 excluding antenna
& installation. Waiting period of some 6-8 weeks for ICASA licence,
not yet in common use by 4x4 users.
The same rules for AM antennas apply to the FM antennas
as well. However, there are two common types available:
* Quarter Wave Antenna, which should once more
be mounted in a central position on a metal surface, but is only
some 400mm or so in length, and
* 5/8 Antenna, normally side- mounted on the door
pillar behind one of the doors. This type of antenna is designed
for this application and will produce good results.
Of the two types, I prefer the former for mountainous
terrain, the latter for flat countryside.
Pictured below are two typical VHF/FM Radios, the
Kenwood TK7102 4-Channel unit, and the Vertex VX2100 8-Channel radio.
Both radios feature Channel Scan if required.
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