Cobra 21 Citizens Band Solid State 2-Way Radio
Instruction Manual
A Product of DYNASCAN CORPORATION
1801 West Belle Plaine Avenue, Chicago, Illinois 60613
Specifications
General
| Channels | 23 |
| Frequency Range | 26.965 to 27.255 MHz |
| Frequency Control | Crystal synthesizer |
| 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., 1.5A; Receive: Squelched, 0.3A; full audio output, .65A |
| Size | 8 1/2" L. x 5-7/8" W. x 2 1/4" H. |
| Weight | 3 1/2 pounds |
| Antenna Connector | UHF, SO239 |
| Semiconductors | 20 Transistors, 11 Diodes |
| Meter | Illuminated, indicates relative power output and received signal strength |
Transmitter
| Power Input | 5 Watts |
| Modulation | High and low level Class B |
| Modulation Capability | 100 % - Adjustable with Microphone Gain Control |
| Frequency Response | 300-2500 Hz |
| Output Impedance | 50 Ohms, unbalanced |
Receiver
| Sensitivity | Less than 1 μV for 10 DB (S+N)/N |
| Selectivity | 6 db @ 4 KHz, 40 db @ 20 KHz. |
| Image Rejection | 30 db |
| I.F. Frequencies | Double conversion, 1st: 11.275 MHz 2nd: 455 KHz |
| Automatic Gain Control (AGC) | Less than 10 db change in audio output for inputs from 10 to 500,000 microvolts |
| Squelch | Adjustable; threshold less than 1 μV. |
| Audio Output Power | 2.5 Watts into 8 Ohms |
| Frequency Response | 300-3000 Hz |
| Distortion | Less than 10 % @ 2.5 Watts @ 1000 Hz |
| Built-in Speaker | 8 Ohms, round |
| External Speaker (Not Supplied) | 8 Ohms; disables internal speaker when connected |
PA System
| Power Output | 3 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 |
The Cobra 21 has been designed to provide high level, trouble-free performance in the Citizens Radio Service.
Channel Frequencies
| Channel | Channel Frequency in MHz | Channel | Channel Frequency in MHz |
| 1 | 26.965 | 12 | 27.105 |
| 2 | 26.975 | 13 | 27.115 |
| 3 | 26.985 | 14 | 27.125 |
| 4 | 27.005 | 15 | 27.135 |
| 5 | 27.015 | 16 | 27.155 |
| 6 | 27.025 | 17 | 27.165 |
| 7 | 27.035 | 18 | 27.175 |
| 8 | 27.055 | 19 | 27.185 |
| 9 | 27.065 | 20 | 27.205 |
| 10 | 27.075 | 21 | 27.215 |
| 11 | 27.085 | 22 | 27.225 |
| 23 | 27.255 |
These transceivers have been designed for use in Class "D" operation in the 11 meter Citizens Radio Service. Operation is subject to FCC regulations, Part 95. A completed FCC Form 505 must be submitted prior to operation.
Warning: Transmitter section adjustments must be performed by a qualified technician holding a valid first or second class FCC radiotelephone License.
Installation
Location
Plan the location of the transceiver and microphone bracket before starting the installation. Select a location that is convenient for operation and does not interfere with the driver or passengers in the vehicle. In automobiles, the transceiver is usually mounted to the underside of the dash panel, with the microphone bracket beside it.
Mounting and Connection
The Cobra 21 is supplied with a universal mounting bracket. The transceiver is held in the bracket by two bolts, permitting adjustment at the most convenient angle.
- After determining the most convenient location, hold the Cobra 21 with mounting bracket in the exact position. Use the mounting bracket as a template to mark the location for the mounting bolts. Drill holes and ensure nothing will interfere with the installation.
- Connect the antenna cable plug to the standard receptacle on the rear panel.
- Connect the DC power input wire (with fuse) to +12 V DC. In automobile installations, this is typically the accessory contact on the ignition switch.
- Connect the black leads to -12 V DC, usually the vehicle chassis. Ensure good electrical contact (remove paint if necessary).
- Mount the microphone bracket on the right side of the transceiver or near it, using the supplied screws. Place the bracket so the microphone is readily accessible.
Ignition Noise Interference
Electrical noise from the vehicle's generator and ignition system can limit mobile receiver performance. The Cobra 21 has a selectable automatic noise limiter (ANL). If ignition interference is severe, consult a COBRA dealer or a 2-way radio technician for assistance in locating and correcting the noise source.
Antenna
The antenna is crucial for transmission distance. A properly matched 50 Ohm antenna system is required for maximum power transfer. For mobile installations, a non-directional antenna is recommended. A vertically polarized quarter-wavelength whip antenna is ideal for 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. A standard antenna connector (Type SO-239) is provided for easy connection to a PL-259 cable termination.
If the transceiver is not mounted on a metal surface, a separate ground wire from the unit to a good metal electrical ground in the vehicle is necessary. For boat installations, a ground plate or a steel hull is required for maximum efficiency. Consult your dealer for information on adequate grounding systems and prevention of electrolysis.
Base Station Operation
For operation from 110-120 V AC house current, the DYNASCAN PAC-24 Power Station (optional equipment) is required. Connect the transceiver's red (+) and black (-) leads to the corresponding terminals of the PAC-24. The PAC-24 operates from a 120-volt 60 Hz power source.
NOTE: Do not attempt to operate this transceiver by connecting directly to 110 Volts AC.
When using the PAC-24 for base station operation, any Citizens Band antenna (beam, dipole, ground plane, or vertical) may be used. A ground plane vertical antenna provides uniform horizontal coverage.
Remote Speaker
The external speaker jack (EXT. SPKR.) on the rear panel is for remote receiver monitoring. The external speaker should have 8 Ohms impedance and be able to handle at least 3 watts. Plugging in an external speaker disconnects the internal speaker.
Public Address
For Public Address (PA) system use, an external 8 Ohm, 3 watt speaker must be connected to the EXT. SPKR. jack. Direct the speaker away from the microphone to prevent acoustic feedback. Physical separation between the microphone and speaker is important for high volume PA operation.
Operation
Controls and Indicators
The Cobra 21 features six controls and one indicator on the front panel.
- OFF/ON/VOLUME: Turn clockwise to power the unit on and set the listening level.
- SQUELCH: Eliminates receiver background noise in the absence of a signal. Adjust clockwise until noise disappears. Do not advance too far, or weak signals may be missed.
- CHANNEL SELECTOR: Selects one of the 23 Citizens Band channels. Channel 9 is reserved for emergency communications. Channels 10-15 and 23 may be used for communications between stations operating under the same license.
- ANL SWITCH: Activates the automatic noise limiter circuits when set to the ANL position.
- PA-CB SWITCH: Selects operation mode. The PA function requires an external speaker. In the CB position, the PA function is disabled.
- MIKE GAIN: Varies modulation amount during transmit. Functions as volume control in PA mode.
- PWR/S METER: Shows relative transmitter power when transmitting and input signal strength when receiving. Illuminated when power is on.
- PRESS-TO-TALK MICROPHONE: Press the switch to transmit; release to receive. Hold the microphone about two inches from your mouth and speak clearly in a normal voice.
Operating Procedure to Receive
- Place the CB-PA switch in the CB position.
- Turn the VOLUME control clockwise until a click is heard. The microphone must be plugged in for the receiver to operate.
- Set the VOLUME for a comfortable listening level.
- Turn the SQUELCH control slowly clockwise until the receiver background noise just disappears.
- Set the CHANNEL selector switch to the desired channel.
Operating Procedure to Transmit
- Select the desired channel.
- If the channel is clear, depress the push-to-talk switch on the microphone and speak clearly in a normal voice. The output lamp will light, indicating proportional output power.
Accessory Circuit Operation
- ANL Operating: Slide the ANL switch to the ANL position to activate the automatic noise limiter circuits.
- Public Address (PA) Operation: Connect an 8 Ohm, 3 watt speaker to the EXT. SPKR. jack. Ensure physical separation between the microphone and the speaker to prevent acoustic feedback, especially at high volumes. Disconnecting the antenna cable can provide complete elimination of outside signals.
Maintenance and Adjustment
The transceiver is designed for mobile installations with solid-state circuitry for high reliability. Replace parts only with identical parts. Refer to the schematic diagram and parts list.
WARNING: Federal law requires that adjustments to the radio frequency section of this transceiver may only be made by a U.S. licensed first or second class commercial license holder (FCC Part 95D, Section 95.97d).
Adjustment
The transceiver is factory aligned and should not require adjustment with a 50 Ohm antenna. If a non-50 Ohm antenna is used, transmitter output circuit adjustment for optimum power transfer may be made by qualified personnel using a high-quality in-line r-f wattmeter.
If performance issues arise, review operating instructions. If problems persist, refer to the WARRANTY SERVICE INSTRUCTIONS.
Warranty Service Instructions
- Refer to the instruction manual for applicable adjustments.
- Check common electrical parts. Consult the manual for applicable adjustments after replacement.
- Defective parts within the warranty period should be sent to the factory prepaid, with product model and serial number, and date of purchase. These parts will be exchanged at no charge.
- If issues are not resolved, pack the product securely in its original packaging. Include a detailed list of troubles, your name, and address. Forward prepaid to the nearest Dynascan authorized communication service agency.
Contact your local Dynascan Distributor for service agency information or write to:
Service Department
DYNASCAN CORPORATION
1801 West Belle Plaine
Chicago, Illinois 60613
Limited 90-Day Warranty
DYNASCAN warrants its products against defects in material and workmanship for ninety (90) days from the date of purchase from an authorized distributor. DYNASCAN will, at its option, repair or replace any non-conforming product or component returned transportation prepaid to their factory or authorized service contractor. DYNASCAN is not liable for any consequential damages. This warranty is limited to ninety (90) days and does not cover damage from unauthorized alterations, misuse, negligence, accident, or improper installation/adjustment. The warranty is void if the serial number is altered, defaced, or removed. DYNASCAN reserves the right to discontinue models or change specifications without notice. To register this warranty, complete and mail the enclosed DYNASCAN warranty registration card to DYNASCAN, 1801 W. Belle Plaine Avenue, Chicago, Illinois 60613, within five (5) days of purchase.
