ADJUSTING THE SWR
- Turn the transmitter off.
Disconnect the antenna coaxial cable at the transmitter output.
- Connect the "TRANS"
connector on the meter to transmitter output with a short jumper cable and
"ANT" to antenna coax.
- Set the center switch to
"FWD" or "Calibrate" and rotate the adjusting knob to near minimum
position.
- Turn the transmitter on,
rotate the calibration knob for full meter swing or to the calibration set
line.
- Next, set the switch to
"REF" or off the calibration position.
- Read the meter scale.
- The indicator will give
the SWR reading directly.
- A perfect matching of
1:1 ratio is ideal .
- An SWR of 1.8:1 is
considered satisfactory, taking into account the line losses and slight
mismatching.
- Adjustments on the
transmitter and antenna system should be made so that the SWR is as low as
possible.
- (*note - readings are
always taken with the transmit lever depressed.)
BEFORE TUNING
- Clean and check all
grounds.
- A sure way to get a good
ground is to run a wire from an antenna mounting bolt and the transmitter to
an earthen grounding rod on a base station or frame ground on a mobile.
- Check for infinite
resistance between the antenna element and the base on a mobile antenna. If there is continuity,
don't try to transmit. Possible cause may be a crushed antenna cable causing
an electrical short.
- Check cable coax
connections, clean, tight, with no moisture.
|
SWR RATIO |
REFLECTED POWER % |
| 1:1 |
0 |
| 1.2:1 |
0.8 |
| 1.3:1 |
1.6 |
| 1.4:1 |
3.2 |
| 1.5:1 |
4 |
| 1.6:1 |
5 |
| 1.7:1 |
5.3 |
| 1.8:1 |
8 |
| 1.9:1 |
10 |
| 2:1 |
11 |
TUNING NOTES
- The antenna should be outside
and at least 15 feet from any buildings or large objects such as trees.
- Do not touch the antenna
while transmitting.
- Do not let anyone stand
close to the antenna. it will throw your SWR reading way out.
- Objective is to obtain an
SWR of less than 2 to 1 (2.0:1) on all channels from 1 to 40.
- If you experience a
high SWR on all channels you are probably experiencing a ground plane
deficiency. recheck all your cables and grounds.
- If the SWR on channel 40
is greater than that on channel 01, the antenna is considered to be 'long'
and reduction of physical length is necessary.
- On m/c antennas with a
center loading coil, adjustment is made after loosening the top Allen
screws.
- If it is required to cut
the antenna, the amount that you cut off should be in increments of no
longer than 1/8th of an inch.
- Remember, cutting is your
last resort after all possible trouble areas have been eliminated.
- If the SWR on channel 01
is greater than that on channel 40, your antenna is considered to be
'short'.
- You should recalibrate the meter each time
you make a channel change or adjustment in
antenna length.
- Coax for 50 ohm systems
employing a single CB antenna should be RG-58A/U.
- Dual or co-phased systems
require a 75 ohm cable, RG-59A/U.
- Cables supplied with CB
antennas should not be cut or shortened as they are a predetermined length.
- Do not tightly coil excess
cable as this will effect your SWR.