Tuning the antenna.
About tuning antennas.
All antennas should be tuned for the
frequencies they are to be used on. This includes antennas used for receivers.
The main reasons for tuning the antenna are:
1. Performance. The antenna will only perform at its best if it is correctly
tuned.
2. With transmitters such as CBs, incorrect tuning can cause damage to the
transmitter output.
3. Transmitting on a poorly tuned antenna may also cause interference to TV,
radio, etc.
Antennas for receivers usually come pre-tuned but this is not the case with
CB antennas.
Tuning a
CB antenna is usually
just a matter of adjusting the length for the lowest
SWR reading.
The SWR meter.
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Common features of a
SWR
meter include:
* Meter - to see the reading.
* FWD/
SWR (or
SWR/REF) switch - to
switch mode.
* Calibrate control - to adjust the meter for the amount of power used.
* FS function - To measure the strength of the signal from your antenna.
* antenna - for taking field
strength readings.
* Power meter function - To measure radio output.
Some are not necessary for
SWR measurement or tuning the antenna, but may
be handy functions for the more advanced CBer.
Connecting the SWR meter.
On the back of the
SWR
meter, there will be two sockets (known as SO239 connectors). One of these should
be connected to the
CB radio,
and the other to the antenna. The sockets should be marked up to show which one
goes where.
Connecting these the wrong way will not damage any of the equipment, but the FWD
and REF switch functions will be swapped (FWD will read as REF and vice-versa).
The best position to place the meter is close to the antenna, with a short lead
from the meter to the antenna. However, this may be inconvenient, so the
alternative is a short lead from the radio, with the main coax running from the
meter to the antenna.
As the meter uses the power coming from the
CB to take the measurements, an additional power
supply is not needed for
SWR
readings.
