CB
Radio Antenna Adjustment
Here's
a step-by-step
method of adjusting the antenna to give you the
best signal. It worked like a champ for me - I reached out almost 20
miles while on the interstates this past week. I don't take any claim
in writing it - just yanked it off of the net and used it. Maybe this
will help someone in getting ready for your next weekend trip.
Your CB/Ham Field-Strength SWR Meter helps you tune your CB or amateur
radio system for the best performance.
CB and amateur radio systems work best when the antenna system's
impedance matches the transmitter's output impedance as closely as
possible. The meter's standing wave ratio (SWR) function helps you trim
your antenna to the precise length you need for the maximum transmitted
power.
The meter's field strength function helps you position your antenna for
the best coverage and determine the effectiveness of changes you make
to your antenna, antenna cable, and transmitter.
MEASURING
SWR
Measuring
SWR shows you
how much of your radio's transmit power is
reflected from the antenna back into the antenna cable, generating heat
and wasting power. With this information, you can adjust the length of
your antenna or antenna cable so your antenna and radio combination can
produce the maximum power they are capable of producing.
CONNECTING
THE METER
To
connect this meter to
your CB or amateur radio and your antenna, you
need coaxial cable (50 ohm such as rg-8x) with a PL-259 connector on
both ends . The cable must reach from the back of the meter to your
radio's antenna jack.
Follow these steps to connect the meter to your radio and antenna.
1. Turn off your radio. Then disconnect the antenna from the radio and
plug it into ANTENNA on the back of the meter.
2. Plug the coaxial cable into the radio's antenna jack and into
TRANSMITTER on the back of the meter.
CALIBRATING
THE
METER/MEASURING SWR
1.
Set CALIBRATION switch
on the front of the meter to FWD.
2. Turn on your radio. Then select a channel or frequency on your
transmitter and hold down its transmit key. Do not speak into the
microphone.
Notes: An SWR reading will be different for different frequencies
(channels). If you transmit on one channel more often then any other,
select that channel. If you transmit on several channels, choose a
frequency in the middle of the range of channels you use. (For example,
if you transmit on all 40 CB channels, choose Channel 20, because it is
midway between Channel 1 and Channel 40.)
If you use a CB that has sideboard modes (SSB), do not select any of
these modes. (Use only AM for SWR measurements).
If you have an amateur radio, select the continuous wave (CW) or tuning
mode to check the SWR.
3. While you hold down the transmit key, rotate the meter's knob until
the needle points to CAL.
4. Release the transmit key, then set CALIBRATION switch to REF.
5. Press the transmit key again, then read the SWR by noting the
needle's position on the upper SWR scale. A meter reading of 1 on the
upper scale is ideal. The figure shown between the upper and lower
scales on the meter (% REF POWER) indicates the percentage of power
that is wasted through reflection of the signal from the antenna back
into the antenna cable. For example, an SWR reading of 1.5 also means
that 4% of your signal power is lost. However, 96% of the radio power
is more than enough for almost all applications.
6. Repeat Steps 1-5 for each channel or frequency you want to get an
SWR reading for.
INTERPRETING
SWR READINGS
An
ideal SWR reading is
1.0, but this reading is usually possible only
under laboratory conditions or with a dummy load. Actual antenna
installations have higher readings. The information below will help you
interpret the readings you get.
SWR / Efficiency / Interpretation
1.0 to 1.3 Excellent The antenna cable and the
antenna length match the
transmitter's output requirements almost perfectly. (Most desireable
for power applications)
1.3 to 1.8 Very Good - The antenna, the cable, and the transmitter
operate very efficiently.
1.8 to 2.2 Acceptable - The antenna, the cable, and the transmitter
operate with some loss. If possible, adjust your antenna or antenna
mounting system to improve.
Above 3.0 Inefficient - Adjust your antenna or antenna mounting system
to improve efficiency
IMPROVING
SWR
There
are several ways to
improve the SWR of your radio/antenna
combination. Try these first.
Be
sure you are using the
type of cable recommended for your equipment.
If the manufacturer recommends a 50-ohm cable, do not substitute
another type that has a different impedance.
Confirm
that you mounted
your antenna according to
the manufacturer's instructions. The angle and the base arrangement can
affect the SWR reading.
Adjust
the length of your
antenna according to the
instructions provided by the manufacturer. A change of as little as 1/8
inch can make a measurable difference.
I hope this helps somebody and if you have any questions, let me know!
