Comet CAT-300 Antenna Tuner

The Comet CAT-300 is a manual antenna tuner designed to optimize the performance of amateur radio systems across a wide range of bands. It facilitates efficient power transfer between a transmitter and various antenna types, including dipoles, verticals, mobile whips, and long wire antennas.

Function Description

The primary function of the CAT-300 is to match the impedance of a transmitter to that of an antenna, thereby minimizing reflected power and achieving a low Standing Wave Ratio (SWR). This ensures that the maximum possible power from the transmitter is radiated by the antenna, improving signal strength and clarity.

The device incorporates a precision cross meter that simultaneously displays forward power (FWD), reflected power (REF), and SWR. This allows operators to monitor the tuning process in real-time and make precise adjustments. The meter scale is illuminated, which is particularly useful for operation in low-light conditions, requiring an external DC power supply.

The tuning process involves adjusting two main controls: "TR TUNE" and "X TUNE." The "TR TUNE" knob controls a variable capacitor on the input (transmitter) side, while the "X TUNE" knob controls a variable capacitor on the output (antenna) side. These adjustments allow the operator to manipulate the impedance matching network to achieve the desired SWR.

A "BAND" switch allows selection of the appropriate frequency band (1.8 MHz - 50 MHz), ensuring the tuning components are configured for optimal performance within that range. The "ANTENNA" switch enables selection between two antenna inputs (ANT1 or ANT2) for coaxial connections, or a dedicated terminal for single-wire antennas (ANT2 Terminal).

The "TUNER" switch allows the operator to enable or disable the antenna tuner function. When set to OFF, the CAT-300 acts solely as an SWR meter, allowing for monitoring without active tuning. An "AVG/PEP" switch determines whether power measurements are displayed as average or peak envelope power (PEP).

Important Technical Specifications

Frequency Range: 1.8 – 50 MHz (covering 11 amateur bands)
Input Impedance: 50 Ω
Maximum Transmit Power: 300W (SSB)
Output Impedance: 10 – 600 Ω
Minimum SWR Measurement Power: 6 Watts
Lighting Power Supply: DC11V – 15V, Approx. 250 mA (external)
Dimensions: 250(W) x 98(H) x 242(D) mm
Weight: Approx. 2.7 kg (approx. 6 lbs)

Usage Features

The CAT-300 is designed for ease of use, with a clear layout of controls and indicators.

Connection Procedures: High-quality 50-Ohm coaxial cables (e.g., 3D-2V, 5D-2V, RG-8X, RG-213, or "400" type) are recommended for connecting the radio to the CAT-300 and the CAT-300 to the antenna(s). For long wire antennas, the dedicated ANT2 terminal should be used, and the ground wire connected to the GND terminal. It is crucial to connect the CAT-300 to an earth ground via the GND terminal to reduce TVI (Television Interference) and BCI (Broadcast Interference).

Operation for Reception (SWL): For reception-only use, the TUNER switch should be enabled. The BAND switch, TR TUNE, and X TUNE controls are then adjusted to maximize the received signal level. A provided tuning table offers starting point settings for these adjustments.

Operation for Transmission:

Antenna Selection: Set the ANTENNA switch to the appropriate position (ANT1, ANT2, or ANT2 Terminal) corresponding to the connected antenna.
Power Reduction: Reduce the transmitter power to between 5 and 10 Watts during the tuning process. This is a critical precaution to protect both the transmitter and the tuner from high RF voltages and fluctuating impedances.
Initial Settings: Set the BAND switch to the desired frequency band and use the provided tuning table to set the TR TUNE and X TUNE controls to their approximate starting points. These values are based on a 50Ω input impedance and load and serve as a guide.
Initial Tuning: Apply transmitter power (CW, AM, or modulation) until the reflection power meter needle deflects.
TR TUNE Adjustment: While transmitting, slowly turn the TR TUNE dial to find the point where the meter deflection (reflected power/SWR) is minimized.
X TUNE Adjustment: Next, turn the X TUNE dial to further minimize the SWR meter deflection.
Refinement: Repeat steps 4-6 to fine-tune the TR TUNE and X TUNE controls until the SWR is minimized, ideally below 1.5:1.
Band Adjustment (if needed): If a low SWR cannot be achieved, immediately stop transmission. Set the BAND switch one step lower and resume the tuning process from step 4.
Full Power Operation: Once a low SWR is obtained, the system is ready for operation up to the maximum transmission output of 300 Watts.

Maintenance Features

The CAT-300 is designed for reliable operation with minimal maintenance.

Precautions for Longevity:

Power Limit during Tuning: Always limit transmitter power to 10 Watts or less during tuning to prevent damage from high RF voltages and impedance fluctuations.
Band Switch Operation: Never operate the BAND switch while the transmitter is transmitting, as this can cause a temporary increase in SWR to infinity, potentially damaging the transmitter or tuner.
Maximum Power Limit: Do not apply transmitter power of 300 Watts or higher to the CAT-300, as this can lead to malfunction or damage.
Antenna System Optimization: While the CAT-300 can tune loads between 10-600 Ohms, it is recommended to optimize the antenna system itself if the initial SWR is outside the range of 2.5:1, rather than relying solely on forced tuning.
Power Supply for Illumination: Do not apply 15V DC or higher, or any AC voltage, to the external power supply input for the meter scale lamp. Using an incorrect power supply can cause malfunction and/or damage.

The CAT-300 is manufactured to strict quality standards, but users are advised to inspect the unit upon receipt for any shipping damage. In case of damage, the dealer should be contacted. Regular cleaning of the exterior with a soft, dry cloth is generally sufficient for maintenance. The product's appearance and specifications are subject to change without notice for continuous improvement.

Comet Antenna CAT-300 - Page 2

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