These days almost every 4WD will have a UHF fitted or a handheld unit sitting in the glovebox and not
a lot of people give them a lot of thought they seem like a pretty simple bit of gear you press
the button talk to your mates and then they talk back to you but there's some tips tricks and info
that you can take advantage of to get the best out of the UHF so first let's start with the basics
UHF stands for ultra high-frequency and in Australia that means that the UHF in your
fall drive operates between about four hundred and seventy six megahertz and four hundred and seventy
seven megahertz there are some other commonly used radio bands as well you've probably heard
of VHF and HF they simply transmit and receive at lower frequencies and as a general rule lower
frequencies means greater transmitting distance the benefit of UHF with its shorter range is
that many more people can use it in different areas without their conversations overlapping
UHF communication is generally limited by line-of-sight and while there are different
radios with different transmitting power they more account for obstacles and obstructions rather than
actual outright transmission distance if you can increase your line of sight and decrease
the amount of obstructions and obstacles in your path you can greatly increase your sending and
receiving distance a really easy way to do that is to increase your height if you're sitting on top
of the mountain and your mate sitting on top of a mountain you'll have a much greater transmitting
distance equally if you're on top of the mountain and your mates in the bottom of a valley as long
as you can see each other you'll improve that transmitting and receiving distance the other
thing that affects line-of-sight is the curvature of the earth so if your eyes are about two meters
above sea level you can see approximately five kilometres to the horizon if you had a mate over
the horizon further five kilometres although you wouldn't be able to see each other if you both
were using a UHF the radio waves would intercept so there's a pretty easy calculation to figure
out your theoretical maximum UHF range that is three point five nine times by the square root
of the height in metres of your antenna so three point five nine times the square root of two if
it's two metres so if you're sitting in your full drive on top of a mountain and your antenna was a
hundred metres high it would have an effective theoretical range of over 35 kilometres if your
mate was also on a hundred meter high mountain and a double 270 kilometres but in the real world
you're going to obstacles and obstructions and that's when a more powerful UHF comes in handy
well it's not able to punch through a mountain a higher powered UHF will have more of a chance of
getting through dense bush or foliage the next important factor that affects your UHF range is
the type of antenna you choose where you mount it and its gain in terms of the construction of
your antenna the first type is a whip that is what you see is what you get this part is the
transmitting and receiving part of the antenna the other option is a radome antenna where the
intent is actually hidden inside a protective covering generally fibreglass now that does
minimally affect the signal strength and receiving capabilities but they're better suited to harsh
off-road conditions the next thing to look out for is whether it's a ground independent or non
ground independent antenna now basically an on ground independent antenna relies on its base
and the surrounding metal area to transmit and receive signals they need a fairly large
flat horizontal surface to bounce the radio waves whereas a ground independent antenna doesn't need
that same horizontal surface no matter where you mount it it'll have the same output pattern the
best place to position an on ground independent antenna is in the centre of your roof if you
mount it on the bull bar or to either side of the vehicle it affects the output pattern negatively
another thing to look out for is elevated feed and what that means is that rather than the
antenna measurements starting from the very base it actually starts partway up the full antenna
length so you're getting a slight height advantage and a slight distance communication advantage now
the most important thing to look for when you're choosing an antenna is the gain generally listed
these days in DB I which is decimals isotropic an isotropic antenna is theoretically an antenna
with a perfectly spherical output pattern and no gain so DB I is telling you how many
decibels it is above that baseline while this theoretical isotropic antenna is putting out
a perfect sphere when you're actually getting is more of a doughnut shape and as you increase the
gain you're squeezing it down vertically so it's shrinking and range vertically but then increases
horizontally so a theoretical isotropic antenna would look something like this with two to four
DB I have gain in the real world this is what you're looking at between five to seven DB I
you'd get something like this and an antenna over 8 DB i it would look like this each of
these different antennas with different gains has their own strengths and weaknesses so a low gain
antenna with its fairly large vertical spread and fairly small horizontal spread makes it ideal in
hilly or mountainous terrain a medium gain antenna adds a fair bit of range horizontally but loses
some of that vertical spread so it's more of an all-round setup and finally a high gain antenna
adds a lot of horizontal spread at the expense of any vertical reach so it's great for flat
terrain and getting the maximum distance from UHF in deserts or Outback driving some units give you
the option of multiple different antenna lengths on the same base and that means you can have one
antenna to suit a bunch of different destinations you can get switches that allow you to connect two
different antennas to the one UHF unit but they introduced so many losses into the system that all
they end up doing is reducing the effectiveness of UHF radio significantly lastly the coaxial cable
that's connected to your antenna is sensitive and needs to be treated with care you can cut
these down to length so long as you make sure you rejoin them correctly because if you increase the
impedance in this cable the performance of your UHF will suffer similarly you shouldn't bunch this
cable up tightly behind the dash for example and it shouldn't be subjected to tighter bends than
about six centimetres between these two points now if you do that you can damage the internals
which will mean the signals rather than traveling through the cable have a tendency to bounce back
increase noise and reduce effectiveness one last thing to be aware of whether you're installing
your antenna sitting in your full drive using UHF or using a handheld is to try and keep this
antenna as vertical as possible that means that when you're using it that horizontal pattern is
spreading evenly by changing the angle you actually change the output direction another
way to make sure you're getting the most out of your you H F is to understand it's more advanced
functions things like CT CSS and DC s now that stands for continuous tone coded squelch system or
digitally coded squelch and they're basically ways that you can use the same channel as a near-by for
driver without being able to hear them they're a similar system in that they let you choose what
could be called a subchannel within the channel that you're on if another full driver has selected
the same sub channel you'll be able to communicate otherwise both your radios will be muted to each
other with 38 CT CSS codes and a hundred and four dcs codes so long as you and your mates
have chosen a channel and a code before your trip it's very unlikely anyone else will interrupt you
most importantly you need to know which channel you should be using and when with modern UHF
radios offering 80 channels ranging from simplex to duplex channels for emergencies only and for
telemetry it's important you get this right simplex channels are the most basic and what
you'll most often be using they're ideal for general chat from radio to radio duplex
channels extend the range of your UHF by using repeater stations across Australia a repeater
is a special type of radio that receives a signal on one channel and outputs it on another channel
that's why you need a duplex function on your UHF this duplex function could push your signal
a further 80 kilometres in some areas channels 5 and 35 are designated for emergencies while 22 and
23 are for data telemetry then there's a couple of other channels like 10 11 18 and 40 that have
traditional uses whether that's the national parks convoys truck ease or highways for an
easy glove box guide check out the downloadable PDF in the description for all the channels and
remember UHF in Australia is public which means basically anyone can get on their transmit and
receive so try and keep it civil and please stay off those emergency channels unless you need them
because there are big fines for misuse remember that families often have the UHF on when they're
driving so what's your language when you're on the radio and if you're out in the sticks and
pull into a little town don't forget that pubs servos and houses often have their radios on scan
so don't say anything over the radio that you wouldn't say to someone face to face as always
make sure you leave a comment if you've got any questions or suggestions and check out the rest of
the channel for more 12-volt camping four wheel driving and cooking tips tricks and techniques