The Sommerkamp TS-680DX is a Citizens Band (CB) transceiver designed for continuous heavy-duty mobile and base station applications. It operates on 80 channels within the 26.965 to 27.755 MHz (11-meter) citizens band, utilizing Amplitude Modulation (AM/A3) for both transmission and reception.
Function Description:
The transceiver's primary function is two-way radio communication on the CB band. It incorporates advanced features for enhanced performance and user convenience.
Receiver Section:
The receiver is a double conversion superheterodyne design, controlled by a Phase Locked Loop (PLL). It features a unique combination of low-noise Field Effect Transistors (FETs), ceramic, and L/C filters, providing exceptional reception quality. A fully automatic noise limiter (ANL) helps reduce ignition noise pulses, and a high-fidelity speaker amplifier ensures clear audio output. The receiver's power supply for the RF, IF, and oscillator sections is stabilized by a sharp cut-off Zener diode, contributing to high sensitivity and unwanted signal rejection. A separate squelch detector with balanced hysteresis provides high squelch sensitivity. The meter indicates the field strength of incoming signals.
Transmitter Section:
The transmitter section is also PLL-controlled and uses a one-crystal controlled oscillator. Its output is synthesized in a class B mixer, followed by a double-tuned filter, class AB1 buffers, and a highly efficient collector-modulated class C driver and power output stage. These stages are coupled to the antenna jack via series and pi-matching filters. The modulator includes an input audio filter, ALC amplifier, integrated pre-and power amplifier, and a modulation transformer, ensuring low distortion and up to 100% modulation. The input is designed for a 500-ohm dynamic microphone or a 32-ohm speaker/microphone combination with a 1K ohm resistor in series. The meter indicates the output power during transmission.
Receive/Transmit Switching:
Switching between receive and transmit modes is managed by a single-pole, single-throw switch in the microphone, combined with NPN and PNP switching transistors.
Important Technical Specifications:
- Semiconductors: 4 Integrated Circuits, 2 FETs, 22 Transistors, 1 SCR, 23 Silicon diodes, 2 Varicaps, 5 Zener diodes.
- Transmitter System: Synthesized PLL controlled, Collector modulation AM.
- Frequency: 80 Channels on 27 MHz (26.965 to 27.755 MHz).
- Output Power: 10 Watts at 13.8V DC.
- Band Width: 8 KHz (max.).
- Antenna Impedance: 50-52 ohms.
- Receiver System: Double conversion superheterodyne, PLL controlled.
- Sensitivity: 1µV or better for 100mW output, 10 dB signal to noise ratio.
- Intermediate Frequency: 1st I.F. 10.7 MHz, 2nd I.F. 455KHz.
- Receiver Selectivity: 40 dB down at 10 KHz or more.
- Squelch Sensitivity: 1µV.
- Audio Output Power: 2 watts in 10% distortion.
- Power Source: 11-16V D.C. Negative Ground. Fuse 5A.
- Microphone: Dynamic type with press-talk switch, Impedance 500 ohm.
- Speaker: Dynamic type, Voice coil Impedance 8 ohm.
- Size: 156 × 58 × 205 mm.
- Weight: 2.3 kg.
- Accessories: Mounting bracket, Mounting hardware, power cord.
Usage Features:
- Control Locations:
- Front Panel: Power-SW/Volume Knob, Squelch/ANL-OFF Knob, RF Power & "S" Meter, Delta-Tune, Channel Selector Knob.
- Rear Panel: EXT. SP. Jack, Antenna Jack.
- Microphone: Press-to-Talk Button, Microphone Jack, Transmitting Light (Push Call Button), VSWR Light.
- Installation: Designed for mobile (under dashboard) or base station use. Requires connection to a 13.8 Volt DC power supply (red wire to ACC terminal or + battery terminal, black wire to chassis/ground).
- Antenna Connection: Connect a 50-ohm antenna to the antenna jack, preferably with an SWR-Meter inserted in the cable for initial setup.
- Power On/Off & Volume: The Power-SW/Volume knob turns the unit on and adjusts audio volume.
- Channel Selection: The Channel Selector Knob allows selection of any of the 80 available channels. The channel lamp illuminates when the unit is on.
- Squelch Control: The Squelch/ANL-OFF knob adjusts the squelch level to eliminate background noise. Turning it counter-clockwise switches off the Automatic Noise Limiter (ANL).
- Delta-Tune: Used for fine-tuning reception for best clarity.
- Transmitting: Press the button on the microphone and speak normally. The meter needle should move slightly and stay within the red mark.
- Receiving: Release the microphone button to receive. The meter indicates signal strength.
- Circuit Protection: An automatic protection circuit switches off the transmitter if the SWR is too high, indicated by the VSWR light.
Maintenance Features:
- SWR Check: It is crucial to check the Standing Wave Ratio (SWR) of the antenna during initial setup. The SWR must be less than 1:2. Prolonged transmission with a high SWR (above 1:2) can damage the transmitting transistors. The SWR check should be done quickly (within 3 seconds). If the SWR is too high, the antenna should be repaired or replaced.
- Fuse: The unit uses a 5A fuse for power protection.
- Antenna Mismatch Indication: The VSWR light illuminates when the antenna is mismatched, and the transmitting circuit will be cut off to prevent damage.
- Microphone Jack: The 7-pin DIN standard accessory jack provides connections for external speaker, AF out, audio output, microphone input, 12V for VOX unit, and transmit/receive switching. The case is grounded. The transceiver must always be operated with the microphone plug inserted.
The Sommerkamp TS-680DX is a robust and feature-rich CB transceiver designed for reliable communication with high sensitivity, good signal rejection, and effective noise suppression.
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