Cobra Electronics 21 LTD CB Antenna, Ignition Noise Interference, Temporary Mobile Operation

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Installation (Cont.)

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 direc- tion of the body of the vehicle. For all practical purposes, however, the radiation 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 installa- tions. Consult your Cobra dealer for further details, or call 773-889-3087 and speak to a Cobra customer representative.

When installed in a boat, the transceiver will not operate at maximum efficiency without a ground plate, unless the vessel has a steel hull. Before installing the trans- ceiver in a boat, consult your dealer for information regarding an adequate ground- ing 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. Call 773-889-3087 for further information.

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 battery.

Even though the COBRA21 LTD ST has an automatic noise limiter, in some instal- lations ignition interference may be high enough to make good communications impossible. The electrical noise may come from several sources. Many possibili- ties exist and variations between vehicles require different solutions to reduce the noise. Consult your COBRAdealer or a 2-way radio technician for help in locat- ing 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 COBRAdealer. It consists of a 120-volt, 60 Hz AC to 12-volt DC power con- verter 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 COBRAdealer. This adapter and a magnetic mount antenna allow you to quickly "install" your trans- ceiver for temporary use.

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Contents Citizens Band WAY Mobile Radio Cuts Static coming in, adds Punch going out CB StoryMHz SpecificationsChannel Mounting and Connection InstallationLocation Ignition Noise Interference CB AntennaBase Station Operation Operation from 120VAC, House Current Temporary Mobile OperationFront Panel Controls and IndicatorsOperation Rear Panel Operating Procedure to ReceivePress-To-Talk Microphone How SoundTracker Works Operating Procedure to TransmitAdjustment Warning Maintenance and AdjustmentAppendix Code MeaningHow Your CB Can Serve You If You Think You Need ServiceFew Rules That Should Be Obeyed Limited Two Year Warranty Warranty and Service

21 LTD specifications

Cobra Electronics 21 LTD is a versatile Citizen Band (CB) radio designed for seamless communication in a wide array of environments, making it a staple for truck drivers, outdoor enthusiasts, and hobbyists alike. Known for its reliability and quality, the 21 LTD combines advanced technology with user-friendly features, ensuring clear and efficient communication.

One of the standout features of the Cobra 21 LTD is its compact design, which makes it easy to install in trucks, cars, and even boats. Despite its small size, it accommodates a comprehensive 40-channel system, allowing users to select from various frequencies, ensuring they can find optimal communication channels regardless of their location.

Equipped with a powerful, built-in noise-canceling microphone, the 21 LTD is adept at minimizing background noise, producing crystal-clear audio even in noisy environments. This feature is particularly beneficial for truck drivers traversing busy highways, ensuring that both transmitted and received messages maintain high quality. Additionally, the radio boasts Automatic Noise Limiting (ANL) technology, which further enhances sound quality by reducing static and interference.

The Cobra Electronics 21 LTD also includes a front-firing speaker for improved audio clarity and a large, easy-to-read analog gauge for channel selection and signal strength monitoring. This design enhances operational convenience, allowing users to stay focused on the road while effortlessly adjusting settings.

Another notable characteristic is the inclusion of a PA (Public Address) feature, which enables users to connect an external speaker. This is especially useful for communicating with larger groups or providing instructions at job sites. Furthermore, the radio features a built-in SWR (Standing Wave Ratio) meter, an essential tool for ensuring proper antenna alignment and optimizing signal performance.

In terms of durability, the Cobra 21 LTD is designed to endure the rigors of outdoor use, featuring a robust construction that can withstand vibrations and varying weather conditions. With an easy installation process and compatibility with various microphones and accessories, this radio is perfect for both seasoned CB users and newcomers.

In conclusion, the Cobra Electronics 21 LTD is a powerful and reliable CB radio that boasts numerous user-friendly features, advanced technologies, and rugged characteristics. Whether for long hauls, outdoor adventures, or casual communication, the 21 LTD stands out as a top choice for those who value quality and convenience.
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