However a lower gain or less powerful antenna can broadcast better in hilly terrain,
as the angle of the aerial matters less. Lower gain antennas are 3db or lower,
for distance over flat terrain a 6db UHF (ultra
high frequency ) antenna
or higher will suit better.
Even with a lower gain aerial/antenna it still won't guarantee the signal will
be carried 100% clear over a hill.
Hills and buildings can still weaken signals
but a lower gain antenna will increase the chance of carrying a full clear
signal beyond any obstacles.
See diagram below for a clearer explanation.
UHF Antenna 3 dB vs. 6 dB.
Which UHF antenna and what is dB?
or Decibel is a
logarithmic unit (a scale of measurement) that indicates the ratio of a
physical quantity (for scientific details see wikipedia.org ).
Without too much detail every time power is
doubled you add 3 dB. 3 dB is twice the power, 6 dB is 4 times the power, 9 dB is 8
times the power and 12 dB is 16 times the power.
This does not mean that antennas
are only available in 3 dB increments, there are many different dB’s between.
4.5 dB – 6.5 dB are very capable antennas for off roading as they provide great
UHF radio settings:
What is Simplex mode?
mode is the standard operation on the UHF radio; it transmits and receives on
the channel in use.
Line of sight is the normal operating range depending on
which UHF antenna is used.
What is Duplex mode?
Duplex mode is a setting on the UHF radio (see manufactures
manual on how to activate the Duplex mode), its function is to enable
transmitting on one channel whilst receiving on another.
CH 1 on Duplex mode will receive on CH 1 but will transmit on CH 31. The
repeater will receive the message/call on CH 31 and will retransmit on CH 1.
The same goes with CH 2; the UHF will transmit from CH 32 and will receive on
See UHF channel chart for Duplex channels.
Important information when using a Duplex
Duplex mode is recommended
to be permanently ON when using CH 01 to CH 08.
Do not use these
channels in Simplex mode as it will interfere with other users.
The same goes
for CH 31 – CH 38, in this case your voice will be carried hundreds of km away
and could make the repeater unusable during your broadcast.
If Simplex mode
(standard use of UHF CB Radio) is only required, then just keep away from the
Duplex channels and there will be no problems with anyone’s broadcast.
Duplex mode and Repeater towers:
A UHF in a vehicle on simplex mode has limited range. 3-7 km
or line of sight is what the UHF antenna is capable of in most cases.
are hills or large buildings blocking the line of sight the radio signals may
not be transmitted clearly and sometimes not at all.
This is where repeater towers and duplex mode
can assist the two way communication.
Repeater towers are usually found on top of hills, buildings such as water
tanks and broadcast towers.
Using Duplex mode enables the use of repeater towers, with a tower the signal
can be carried around 30 - 100 km away and also enables communication with people
on the other side of the hill/mountain.
Two UHF Antennas on one UHF Radio.
Q: Why use two
A: Well as shown above 3dB works better in hill terrain and
sand dunes, 6dB and higher gain works better on the flat landscape. The idea is
when 4 wheeling in hilly country or sand dunes switch to the 3dB antenna and
when on the highway use the 6dB for better coverage.
Option A: Using two antennas with one CB radio is easy setup
if using a switch to toggle between the two antennas. And works fine with no
problems. Today there are UHF radios, on the market available with 2 antennas outlets.
Option B: Setting up two antennas to feed live signals at
the same time off one UHF CB Radio is possible but not worth the effort
involved. The antennas have to be apart the right amount of distance and the cables
running from the UHF radio to both antennas must be the exact same length,
otherwise there will be interference and all sorts of problems. Its real
technical to setup and the money involved may not be worth it in the end.
Option C: Install two UHF radios with each having its own
antenna, yet you still need to be careful how close the antennas are apart from
each other. It would be wise not to put them both on the same side to prevent