Cobra 21XLR 40-Channel Citizens Band Solid State 2-Way Radio

The CB Story

The Citizens Band (CB) operates between shortwave broadcast and 10-meter amateur radio bands. Established by law in 1949, the Class D two-way communication service opened in 1959. CB also includes Class A business band and Class C remote control frequencies. Unlike a "Ham" license, a Class D license requires no technical knowledge or Morse code proficiency.

In March 1975, the FCC reduced the CB license fee from $20 to $4. A single license covers multiple CB sets for a family or business. Once licensed, anyone can operate the equipment, though the license holder must be over 18. Children or employees can use the equipment, but the licensee remains responsible for legal operation.

Note: FCC regulations permit only "transmissions" (one party to another), not "broadcasts" (to a wide audience). Advertising is prohibited on CB channels as it constitutes broadcasting.

Specifications

General

• Channels: 40
• Frequency Range: 26.965 to 27.405 MHz
• Frequency Control: Phase Lock Loop (PLL)
• Frequency Tolerance: 0.005%
• Operating Temperature Range: -30°C to +50°C
• Microphone: Plug-in type; dynamic
• Input Voltage: 13.8 VDC nom. (reversible ground)
• Current Drain: Transmit: AM full mod. 2A (nominal); Receive: Squelched, 0.5 A; full audio output 1.5 A (nominal)
• Size: 9-3/8"L x 6-1/4"W x 2-1/8"H
• Weight: 3-7/8 pounds
• Antenna Connector: UHF, SO239
• Semiconductors: 21 transistors, 17 Diodes, 6 integrated circuits
• Meter: Illuminated; indicates relative power output and received signal strength

Transmitter

• Power Output: 4 watts
• Modulation: High- and low-level Class B
• Frequency Response: 300 to 3000 Hz
• Output Impedance: 500 ohms, unbalanced

Receiver

• Sensitivity: Less than 1 μV for 10 DB (S+N)/N
• Selectivity: 6 dB @ 7 KHz, 60 dB @ 10 KHz
• Image Rejection: 80dB typical
• Adjacent-Channel Rejection: 60dB typical
• I.F. Frequencies: Double conversion, 1st: 10.695 MHz, 2nd: 455 KHz
• Automatic Gain Control (AGC): Less than 10 dB change in audio output for inputs from 10 to 50,000 microvolts
• Squelch: Adjustable; threshold less than 1 μV
• Audio Output Power: 4 watts
• Frequency Response: 300 to 3000 Hz
• Distortion: Less than 7% @ 4 watts @ 1000 Hz
• Built-in Speaker: 8 ohms, round
• External Speaker (Not Supplied): 8 ohms; disables internal speaker when connected

PA System

• Power Output: 4 watts into external speaker
• External Speaker for PA (Not Supplied): 8 ohms; when PA-CB switch is in PA, the PA speaker also monitors the receiver

FCC Warning

1. Operation requires a valid FCC Station License. Do not transmit until licensed. Illegal operation can result in severe penalties. Read Part 95 of the FCC Rules and Regulations before operating.
2. License applications are made on FCC Form 505, available from FCC field offices. A copy is included with your transceiver.
3. Maintain a current copy of Part 95 of the FCC Rules as part of your Station records. Copies are available from the Superintendent of Documents, GPO, Washington, D.C. 20402.
4. Post your Station License as per paragraph 95.101 of the Rules. Attach an executed Transmitter Identification Card (FCC Form 452-C) to each transmitter. A copy is included with your transceiver.
5. FCC Rules require that transmitter adjustments, other than front panel controls, must be made by or supervised by an FCC-licensed First or Second Class Radio Operator.
6. Replacing or substituting parts with non-recommended parts may violate FCC Rules (Part 95) or Type Acceptance requirements (Part 2).

Installation

Location

Plan the location of the transceiver and microphone bracket for convenient operation without interfering with the driver or passengers. In vehicles, the transceiver is typically mounted under the dash with the microphone bracket nearby.

Mounting and Connection

The COBRA 21XLR includes a universal mounting bracket. The transceiver is secured by four bolts, allowing angle adjustment. Mount the bracket securely using the supplied machine screws and nuts, ensuring a good electrical connection to the vehicle's chassis.

1. Determine the desired location. Hold the transceiver with the bracket in place. If clear, remove the bracket and use it as a template to mark mounting bolt locations. Ensure no obstructions exist before drilling.
2. Connect the antenna cable plug to the standard receptacle on the rear panel. Most CB antennas use a Type PL-259 plug.
3. Connect the DC power input wire (with fuse) to +13.8 VDC. For vehicle installations, this is typically connected to the accessory contact of the ignition switch. This allows operation without the engine running and prevents accidental battery drain. Locate the accessory contact by tracing the power wire from the car's AM broadcast receiver.
4. Connect the black leads to 13.8 VDC. This is usually the vehicle's chassis. Ensure good electrical contact by removing any paint from the connection point.
5. Mount the microphone bracket to the right of the transceiver or nearby, using the supplied screws. Position it for easy microphone access, typically under the dash in a car.

Ignition Noise Interference

Electrical noise from the vehicle's generator and ignition system can limit receiver performance at low signal levels. Operating the vehicle engine turned off can help, as the unit requires minimal current. If ignition interference is severe, consult a COBRA dealer or a 2-way radio technician for assistance in locating and correcting the noise source. The COBRA 21XLR features a selectable automatic noise limiter (ANL).

Antenna Matching

Maximum transmission distance is influenced by the antenna system. A properly matched antenna ensures maximum power transfer. For mobile installations, a non-directional antenna is recommended. A vertically polarized quarter-wavelength whip antenna offers reliable operation and range. Shorter, loaded whip antennas are more compact and suitable when maximum distance is not critical.

Mobile whip antennas use the vehicle's metal body as a ground plane. Mounting at a vehicle corner can cause slight directionality, but for practical purposes, the radiation pattern is non-directional. The transceiver has a standard Type SO-239 connector for easy antenna connection.

If the transceiver is not mounted on a metal surface, a separate ground wire to a good electrical ground in the vehicle is necessary. For boat installations without a steel hull, a ground plate is required for maximum efficiency. Consult your dealer for proper grounding systems and to prevent electrolysis.

Base Station Operation

For operation from 110-120 VAC house current, use the DYNASCAN Model CA-20 Power Pak. This AC-DC power converter delivers the required 13.8 VDC. Connect the transceiver's red (+) and black (-) leads to the CA-20 terminals. Do not connect the transceiver directly to 110 volts AC.

When using the CA-20 Power Pak for base station operation, any Citizens Band antenna (beam, dipole, ground plane, or vertical) can be used. A ground plane vertical antenna provides uniform horizontal coverage.

External Speaker

The EXT. SPK. jack on the rear panel allows for remote receiver monitoring. Use an 8-ohm speaker capable of handling at least 4 watts. Plugging in an external speaker automatically disconnects the internal speaker.

Public Address

To use the transceiver as a public address (PA) system, connect an 8-ohm speaker (minimum 4 watts) to the PA SPK. jack on the rear panel. Position the speaker away from the microphone to prevent acoustic feedback. Physical separation is crucial for high-volume PA operation.

Operation

Controls and Indicators

The COBRA 21XLR features seven controls and two indicators on the front panel:

• OFF/ON/VOLUME: Turn clockwise to power on and set listening level.
• SQUELCH: Eliminates receiver background noise. Adjust clockwise until noise disappears. Further rotation increases the threshold for receiving signals.
• CHANNEL SELECTOR: Selects one of the forty Citizens Band channels. Channel 9 is reserved for emergency communications.
• ANL SWITCH: Activates the automatic noise limiter in the audio circuits when set to ANL.
• PA/CB SWITCH: Selects operation mode. In CB mode, PA function is disabled. In PA mode, a PA speaker must be connected. PA volume is controlled by the DYNAMIKE knob.
• DYNAMIKE: Adjusts microphone gain in transmit and PA modes. In PA mode, it functions as the volume control.
• DIMMER CONTROL: Adjusts the brightness of the LED channel readout.
• PRESS-TO-TALK MICROPHONE: Press the switch to transmit; release to receive. Hold the microphone about two inches from your mouth and speak clearly. The unit comes with a low-impedance (500 ohm) dynamic microphone.

Indicator Functions

• S-METER: Indicates the strength of incoming signals.
• RF METER: Indicates the relative RF output power.

Operating Procedure to Receive

1. Set the CB-PA switch to the CB position.
2. Turn the VOLUME control clockwise until a click is heard to turn the unit ON.
3. Set the VOLUME for a comfortable listening level.
4. Adjust the SQUELCH control clockwise until the background noise just disappears. Do not advance further, or weak signals may be missed.
5. Set the CHANNEL selector to the desired channel.

Operating Procedure to Transmit

1. Select the desired transmission channel.
2. Set the DYNAMIKE control fully clockwise.
3. If the channel is clear, press the push-to-talk switch on the microphone and speak in a normal voice.

Alternate Microphones and Installation

For optimal performance, use a low-impedance dynamic or transistorized microphone with a four-lead cable. The cable should provide audio, shield, transmit control, and ground connections.

4-Wire Mic Cable Pinout:

• Pin 1: Audio Shield
• Pin 2: Audio Lead
• Pin 3: Transmit Control
• Pin 4: Receive Control

Prepare microphone leads by cutting them to extend 7/16" beyond the insulating jacket, stripping 1/8" of the ends, and tinning them. Ensure all leads are the same length.

Microphone Plug Wiring:

1. Remove the retaining screw.
2. Unscrew the housing from the pin receptacle body.
3. Loosen the two cable clamp retainer screws.
4. Feed the microphone cable through the housing, knurled ring, and washer.
5. Wire the leads to the corresponding pins in the microphone plug, referring to the provided wiring diagram (Fig. 3). Use minimal heat for soldering and keep exposed wire lengths short to prevent shorts.

Maintenance and Adjustment

The COBRA 21XLR is designed for reliability in mobile installations. Use only identical replacement parts. Refer to the schematic diagram and parts list if a failure occurs.

Note: If performance issues arise, review operating instructions. If the problem persists, refer to WARRANTY SERVICE INSTRUCTIONS.

FCC Warning: Radio frequency adjustments on this transceiver may only be performed by a U.S. licensed First or Second Class commercial license holder, per FCC part 95 section 95.97 d.

Appendix

10 Code

The Citizens Band radio community uses the "10-code" for efficient communication. Below are common codes and their meanings:

A Few Rules That Should Be Obeyed

1. Identify your official licensed call sign at the beginning and end of every conversation.
2. Limit conversations to five minutes, followed by a one-minute break, to allow others to use the channel.
3. Do not overpower others with illegally amplified transmitter power or high antennas.
4. Do not use CB to promote illegal activities.
5. Do not use profanity.
6. Do not play music on your CB.
7. Do not use your CB to sell merchandise or professional services.

How Your CB Can Serve You

• Warn of traffic tie-ups.
• Provide weather and road information.
• Assist in emergencies or breakdowns.
• Suggest dining and lodging locations.
• Make long trips more interesting and help combat fatigue.
• Provide direct contact with your office or home.
• Facilitate making new friends while traveling.
• Offer "local information" to help find destinations.
• Assist law enforcement by reporting drunk or reckless drivers.

Colonel Samuel S. Smith of the Missouri Highway Patrol noted the "amazing" number of drunken drivers, wrong-way drivers, and speeders reported by CB users. He stated that the "potential benefits of CB radio to law enforcement are so great that they far outweigh the disadvantages." He also mentioned that law enforcement operations sometimes benefit from residual warnings relayed long after their operations have concluded.

Use Channel 9 for Emergency Messages Only

The FCC provides the following guidelines for Channel 9 communications:

• Permitted: Reporting a tornado sighting, stating you are out of gas on a highway, reporting a multi-vehicle collision requiring police and ambulance, relaying a weather warning to secure a boat.
• Prohibited: Reporting no tornado sighting from an observation post, stating you are out of gas at your home, reporting smooth traffic flow, general weather advisories to motorists.

Warranty Service Instructions

1. Refer to the MAINTENANCE section of your Cobra instruction manual for applicable adjustments.
2. Defective parts from units within the 90-Day Limited Warranty period should be sent PREPAID to the Service Department. Include the unit's model and serial number and the purchase date. These parts will be exchanged at no charge under the warranty terms.
3. If problems persist after following the above procedures, pack the unit securely (preferably in original packaging or double-boxed). Include a letter describing the problem, your name, and address. Ship PREPAID (UPS preferred) to the nearest Cobra authorized service agency. If the list of agencies is lost, contact your dealer or write to the Service Department.

Service Department:
Cobra Product Group
DYNASCAN CORPORATION
2815 West Irving Park Road
Chicago, Illinois 60618

Limited 90-Day Warranty

DYNASCAN CORPORATION warrants its COBRA Citizens Band Radios and their component parts to be free from defects in workmanship and materials for ninety (90) days from the date of purchase to the original purchaser.

DYNASCAN will, at its option, repair or replace defective units or parts free of charge upon delivery to an authorized COBRA service contractor or the factory service department, accompanied by proof of purchase date (sales receipt).

To obtain warranty coverage, register the CB radio by completing and mailing the enclosed warranty registration card to DYNASCAN Cobra Communications, P. O. Box 35148, Chicago, Illinois 60618, within five (5) days of purchase.

Exclusions: This warranty does not cover misuse, abuse, unauthorized alterations, or repairs. It is void if the serial number is altered, defaced, or removed.

DYNASCAN is not responsible for damages to the product or automobile resulting from improper installation. Some states do not allow limitation of incidental or consequential damages, so the above limitation may not apply.

This warranty grants specific legal rights, and other rights may vary by state.

For convenience, contact your dealer for repairs or referrals to the nearest service contractor. If local service is unavailable, send the unit to Cobra Communications Service, 2815 West Irving Park Road, Chicago, Illinois 60618, packaged to prevent shipping damage.