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7
Installation (Cont.)
Ignition Noise Interference
Use of a mobile receiver at low signal levels is normally limited by the presence
of electrical noise. The primary source of noise in automobile installations is
from the alternator and ignition system in the vehicle. Under most operating
conditions, when signal level is adequate, the background noise does not present
a serious problem. Also, when extremely low level signals are being received, the
transceiver may be operated with vehicle engine turned off. The unit requires
very little current and therefore will not significantly discharge the vehicle bat-
tery.
Even though the COBRA 29 LTD ST has an automatic noise limiter, in some in-
stallations ignition interference may be high enough to make good communica-
tions impossible. The electrical noise may come from several sources. Many pos-
sibilities exist and variations between vehicles require different solutions to
reduce the noise. Consult your COBRA dealer or a 2-way radio technician for
help in locating and correcting the source of severe noise.
Base Station Operation (Operation from 120VAC, House Current)
To operate your transceiver from your home or office, using the regular house
current as the power source, you will require a 12 VDC power pack that has
been specially designed for the purpose. It is available as optional equipment
from your COBRA dealer. It consists of a 120-volt, 60 Hz AC to 12-volt DC
power converter that delivers the required power for the operation of the
transceiver. Simply connect the red (+) and black ( - ) leads of the transceiver to
the corresponding terminals of the power packs.
DO NOT ATTEMPT TO OPERATE THIS TRANSCEIVER BY
CONNECTING DIRECTLY TO 120 VAC.
Temporary Mobile Operation
To operate your COBRA transceiver from a car on a temporary basis, you may
want to purchase an optional cigar lighter adapter from your COBRA dealer.
This adapter and a magnetic mount antenna allow you to quickly "install" your
transceiver for temporary use.
6
CB Antenna
Since the maximum allowable power output of the transmitter is limited by the
FCC, the antenna is one important factor affecting transmission distance. Only
a properly matched antenna system will allow maximum power transfer from
the 50 ohm transmission line to the radiating element. In mobile installations
(cars, trucks, boats, etc.), an antenna system that is non-directional should be
used.
A vertically polarized, quarter-wavelength whip antenna provides the most reli-
able operation and greatest range. Shorter, loaded-type whip antennas are more
attractive, compact and adequate for applications where the maximum possible
distance is not required. Also, the loaded whips do not present the problems of
height imposed by a full quarter-wavelength whip.
Mobile whip antennas utilize the metal body of the vehicle as a ground plane.
When mounted at a corner of the vehicle they are slightly directional, in the di-
rection of the body of the vehicle. For all practical purposes, however, the radia-
tion pattern is nondirectional. The slight directional characteristic will be
observed only at extreme distances. A standard antenna connector (type SO-239)
is provided on the transceiver for easy connection to a standard PL 259 cable
termination. Cobra loaded type antenna models are highly recommended for
most installations. Consult your Cobra dealer for further details, or call 773-889-
3087 and speak to a Cobra customer representative.
WX Antenna
For best reception of weather channels, we recommend dual band antennas
which provide optimum CB and WX reception. If you want more information
about models and prices, call our consumer hotline 773-889-3087.
When installed in a boat, the transceiver will not operate at maximum efficien-
cy without a ground plate, unless the vessel has a steel hull. Before installing the
transceiver in a boat, consult your dealer for information regarding an adequate
grounding system and prevention of electrolysis between fittings in the hull and
water.
3-Way Combination Antennas are available which allow operation of all three
bands (AM-FM & CB), using a single antenna. However, use of this type of
antenna usually results in less than normal transmit and receive range when
compared to a standard-type "Single Band" antenna designed for CB only. The
quality of reception of radio signals is highly dependent on the antenna sys-
tem. Typical CB antennas may not be very efficient when used for WX recep-
tion. Call 773-889-3087 for further information.
Installation (Cont.)