1. Introduction
The MFJ-945E is a compact and versatile mobile antenna tuner designed for amateur radio operators. It covers a wide frequency range from 1.8 MHz to 60 MHz, allowing for efficient operation across various amateur bands. This tuner features a built-in cross-needle SWR/Wattmeter, an antenna bypass switch, and is capable of handling up to 300 Watts of RF power. Its primary function is to match the impedance of your antenna system to the 50-ohm output impedance of your transmitter, ensuring maximum power transfer and minimizing Standing Wave Ratio (SWR).
2. Safety Information
Please read and understand all safety instructions before operating the MFJ-945E Mobile Antenna Tuner. Failure to follow these guidelines may result in personal injury or damage to the equipment.
- High Voltage: This device operates with high RF voltages. Never open the case or attempt to service the unit while it is connected to a transmitter or power source.
- Power Limits: Do not exceed the maximum power rating of 300 Watts. Exceeding this limit can cause damage to the tuner and your transmitter.
- Grounding: Always ensure the tuner is properly grounded to a good earth ground or vehicle chassis ground to prevent RF current flow on control lines and reduce the risk of electrical shock.
- Ventilation: Operate the tuner in a well-ventilated area to prevent overheating.
- Connections: Always disconnect power from your transmitter before making or changing any connections to the tuner.
- Environment: Avoid exposing the tuner to moisture, extreme temperatures, or direct sunlight.
3. Product Features and Controls
The MFJ-945E features intuitive controls for quick and efficient antenna tuning.
Front Panel Controls
Image 1: Front view of the MFJ-945E Mobile Antenna Tuner, displaying the inductance, tune, transmitter, and antenna knobs, along with the cross-needle meter and lamp switch.
- INDUCTANCE Knob (A-L): Selects the appropriate inductance value for tuning.
- TUNE Knob: Adjusts the variable capacitor for fine-tuning the antenna circuit.
- TRANSMITTER Knob: Adjusts the variable capacitor for fine-tuning the transmitter circuit.
- ANTENNA Knob: Adjusts the variable capacitor for fine-tuning the antenna circuit.
- SWR/Wattmeter: A cross-needle meter simultaneously displays Forward Power, Reflected Power, and SWR.
- Power Range Switch: Selects the power range for the wattmeter (300/60 Watts or 30/6 Watts).
- LAMP ON/OFF Switch: Controls the illumination of the SWR/Wattmeter. Requires external 12V DC power.
- BPS (Bypass) Switch: Allows bypassing the tuner circuit while still enabling the SWR/Wattmeter function.
Rear Panel Connectors
Image 2: Rear view of the MFJ-945E Mobile Antenna Tuner, showing the 12V DC input, TRANSMITTER SO-239, ANTENNA SO-239, and GND (Ground) wing nut post.
- 12V DC Input: Jack for connecting an external 12V DC power supply to illuminate the meter lamp.
- TRANSMITTER (SO-239): Connects to the coaxial cable from your transmitter.
- ANTENNA (SO-239): Connects to the coaxial cable leading to your antenna.
- GND (Ground) Post: Wing nut terminal for connecting a ground wire.
4. Setup and Installation
Follow these steps to properly set up your MFJ-945E Mobile Antenna Tuner:
- Unpacking: Carefully remove the tuner from its packaging and inspect it for any signs of damage.
- Placement: Place the tuner on a stable, non-conductive surface in a location that allows for good ventilation and easy access to controls and connections.
- Grounding: Connect a heavy-gauge wire from the GND post on the rear panel to a reliable earth ground or the vehicle's chassis ground. A good ground is crucial for safe and effective operation.
- Transmitter Connection: Using a high-quality 50-ohm coaxial cable, connect the output of your transmitter to the SO-239 connector labeled TRANSMITTER on the rear panel of the tuner.
- Antenna Connection: Connect your antenna's 50-ohm coaxial cable to the SO-239 connector labeled ANTENNA on the rear panel of the tuner.
- Meter Lamp Power (Optional): If you wish to use the meter lamp, connect a 12V DC power supply (not included, e.g., MFJ-1312D) to the 12V DC input jack on the rear panel. Ensure correct polarity.
5. Operating Instructions
The following procedure outlines how to tune your antenna system using the MFJ-945E.
- Initial Settings:
- Set the Power Range Switch to the appropriate range (e.g., 300/60W for higher power, 30/6W for lower power).
- Ensure the BPS switch is in the 'TUNE' position (not bypassed).
- If using the meter lamp, turn the LAMP switch to 'ON'.
- Set the INDUCTANCE, TUNE, TRANSMITTER, and ANTENNA knobs to their mid-range positions as a starting point.
- Transmit Low Power: Set your transmitter to a low power output (e.g., 5-10 Watts) and select the desired operating frequency. Transmit a continuous carrier (e.g., using CW mode or by pressing the PTT button).
- Adjust for Minimum SWR: While transmitting, carefully adjust the INDUCTANCE, TUNE, TRANSMITTER, and ANTENNA knobs. Observe the cross-needle meter. The goal is to achieve the lowest possible SWR reading (ideally 1:1). Adjust the knobs interactively, as changes to one knob may affect the others.
- Fine-Tuning: Once a low SWR is achieved, you can increase your transmitter's power to your desired operating level (up to 300 Watts) and make any final minor adjustments to the tuner knobs for the absolute lowest SWR.
- Reading the Meter: The cross-needle meter provides simultaneous readings. The needle pointing to the right indicates Forward Power, the needle pointing to the left indicates Reflected Power, and where the two needles cross indicates the SWR.
- Antenna Bypass: If you wish to operate without the tuner in the circuit but still monitor SWR and power, set the BPS switch to 'BYPASS'.
Note: Tuning an antenna system can be an iterative process. Patience and small adjustments will yield the best results.
6. Maintenance
The MFJ-945E Mobile Antenna Tuner is designed for reliable operation with minimal maintenance.
- Cleaning: Keep the unit clean by wiping it with a soft, dry cloth. Avoid using abrasive cleaners or solvents.
- Inspection: Periodically inspect all coaxial cable connections and the ground wire to ensure they are secure and free from corrosion.
- Storage: When not in use for extended periods, store the tuner in a dry, dust-free environment.
7. Troubleshooting
If you encounter issues with your MFJ-945E, refer to the following table for common problems and solutions.
| Problem | Possible Cause | Solution |
|---|---|---|
| High SWR cannot be tuned down | Antenna mismatch, faulty coax, incorrect tuning procedure, antenna outside tuner's range. | Check all cable connections. Ensure antenna is resonant near the operating frequency. Re-attempt tuning procedure carefully. Verify antenna is within 1.8-60 MHz range. |
| Meter lamp does not light | No 12V DC power, lamp switch off, faulty lamp. | Ensure 12V DC power supply is connected and functional. Turn LAMP switch to 'ON'. If still not working, the lamp may need replacement (contact support). |
| No power reading on meter | Transmitter not transmitting, incorrect power range selected, faulty connections. | Verify transmitter is operating. Select appropriate power range. Check coaxial cable connections between transmitter and tuner. |
| RF feedback or RFI | Poor grounding, common mode current. | Ensure a solid, low-impedance ground connection. Consider adding a common mode choke (balun) on the antenna feedline. |
8. Specifications
- Frequency Coverage: 1.8 to 60 MHz
- Power Handling: 300 Watts (Maximum)
- Meter Type: Cross-Needle SWR/Wattmeter
- Power Ranges: 300/60 Watts (Forward/Reflected), 30/6 Watts (Forward/Reflected)
- Capacitors: 1000 Volt rated
- Inductor: Efficient Airwound
- Connectors: SO-239 (Transmitter, Antenna), 12V DC Jack, Wing Nut Ground Post
- Dimensions (H x W x D): Approximately 2 x 8 x 6 inches (5.08 x 20.32 x 15.24 cm)
- Weight: Approximately 2.94 pounds (1.33 kg)
- Color: Black
9. Warranty Information
Please note that for this product, all sales are considered 'as is'. For specific warranty details provided by the manufacturer, MFJ Enterprises, please refer to the documentation included with your purchase or visit the official MFJ website.
10. Customer Support
For technical assistance, service, or further inquiries regarding your MFJ-945E Mobile Antenna Tuner, please contact MFJ Enterprises directly. Refer to the manufacturer's official website or the contact information provided in your product packaging for the most up-to-date support channels.
