TUNING THE ANTENNA FOR OPTIMUM SWR
Since there is such a wide variety of base and mobile antennas, this section will
strictly concern itself to the various types of mobile adjustable antennas.
Because the antenna length is directly related to the channel frequency, it must
be tuned to resonate optimally on all channels of the transceiver.
Channel 1 requires a longer antenna than Channel 40 because it is a lower
frequency. Due to the various methods of adjusting antennas for proper S.W.R ,
we have chosen what we think is the optimum method :
A. Antenna with adjustable screws (set screws).
1. Start with the antenna extended and tighten the set screw lightly enough so
that the antenna can be lightly tapped with your finger for easy adjustment.
2. Set your transceiver to Channel 20. Press the PTT (push-to-talk) switch, and
tap the antenna (making it shorter). The S.W.R. meter will show a lower
reading each time the antenna is tapped. By continuing to shorten the
antenna, you will notice the S.W.R. reading will reach a low point and then
start rising again. This means that you have passed the optimum point for
Channel 20.
Extend the antenna a short distance and again follow the procedure above.
When the lowest point has been reached, switch to Channel 1 and then to
Channel 40 and compare S.W.R. readings. They should be almost equal.
NOTE
The proper setting is achieved when the SWR is 1.5 or
below, and when it has the same reading for channels 1
and 40.
B. Antennas which must be cut to proper length
1. Follow the same procedure as above, but adjust the length by cutting in 1/8"
increments until a good match is obtained.
2.
Be very careful not to cut too much at one time, as once it is cut, it can no
longer be lengthened.
3. The whip is easily cut by filing a notch all the way around and breaking the
piece off with pliers.
If your are having difficulties in adjusting your antenna, check the followings :
a. All doors must be closed when adjusting the antenna.
b. Make sure the antenna base is grounded.
c. Check your coaxial cable routing (it may be pinched when routed into the
car.)
d. Try a different location on your car (keeping in mind the radiation pattern
you wish.)
e. Is the antenna perfectly vertical ?
f. Try a different location in your neighborhood. Stay away from large metal
objects when adjusting (metal telephone or lamp post, fences, etc.)
NOTE
The transceiver will operate into an SWR of 2 to 1
indefinitely and sustain an SWR of 20 : 1 for a maximum
of 5 minutes at rated operating conditions .
EXTERNAL SPEAKER
The external speaker jack (EXT. SP.) on the rear panel is used for remote
receiver monitoring. The external speaker should have 8 ohms impedance and
be able to handle at least 4 watts. When the external speaker is plugged in, the
internal speaker is disconnected.
PUBLIC ADDRESS
To use the transceiver as a public address system, connect an external 8 ohms
speaker (4 watts minimum) to the PA. SP. jack located on the rear panel. Direct
speaker away from the microphone to prevent acoustic feedback. Physical
separation or isolation of the microphone and speaker is important when
operating the PA at high output levels.
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