LDG RT-11 - User Manual

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Overview

Technical Specifications
Usage Features
DB-9 Connector Pinout
Operating Modes
Power Level Considerations
Maintenance Features
Warranty and Service
Firmware Upgrades
Technical Support and Feedback

The LDG RT-11 is a remote automatic antenna tuner designed for use with HF and 6-meter ham bands (1.8 to 54 MHz). It is compatible with transmitters or transceivers outputting between 0.1 to 125 watts. The tuner utilizes a "Switched L" configuration with 256 capacitor and 256 inductor settings, along with High/Low impedance options, to offer over 130,000 possible tuning combinations. This L-network design allows it to match most coax-fed antennas, such as dipoles, verticals, slopers, and beams, within its specified performance range. For long wires and dipoles fed with ladder line, an optional LDG RBA-1 external balun (sold separately) can be used. The typical tuning time for the RT-11 is around 3 seconds, with a range of 0.1 to 5 seconds.

Technical Specifications:

Frequency Coverage: 1.8 to 54.0 MHz continuously.
Load Impedance Range: Tunes 6 to 800 ohm loads, achieving a 10:1 SWR, or 3:1 or less on 6 meters.
RF Power Range: 0.1 to 125 watts (50% duty cycle).
Inductor Range: Up to 20 uH.
Capacitor Range: Up to 2700 pF.
Tuning Time: 0.1 to 5 seconds (3.0 seconds typical).
Current Consumption: 7 to 250 mA (100 mA typical).
Power Requirements: 11 to 20 VDC @ 250 mA max.
Enclosure Size: 8.5” x 5.5” x 3.0”.
Weight: 2.5 pounds.

Usage Features:

The RT-11 is designed for remote mounting and operation, either on a tower or near the antenna. It features a water-resistant ABS plastic case with an integral flange mounting bracket to protect its circuitry from rain and normal weather conditions. The tuner is microprocessor-controlled and fully automatic.

Control of the RT-11 requires external circuitry, which is not included with the basic tuner. There are three primary control options:

Optional LDG Remote Control Unit: This unit controls the RT-11 via a 15-foot DB-9 cable (extendable up to 100 feet with shielded cable). It features front panel controls for Bypass, Semi/Auto mode select, and Tune, along with indicator LEDs for 1.5 SWR and Tune mode. Connections for the DB-9 control line, DC power input, and a radio interface are on the back. This remote unit is also necessary when using the FT-100D One Touch Tune from W4RT Electronics.
Special Interface Cables: LDG provides optional custom interface cables (RT-IC for Icom or RT-AL for Alinco) to connect the tuner directly to compatible transceivers. For Kenwood TS-50 radios, the LDG K-OTT interfaces directly to the ACC port. These cables typically provide power to the RT-11 from the radio, eliminating the need for an external power source. When connected, pressing the tuner button on the radio automatically initiates a tuning cycle, typically setting the radio to CW mode at 10 watts output. The tuner then signals the radio upon completion, and the radio reverts to its previous mode and power settings. Wiring diagrams for homemade Icom or Alinco control cables are available on the LDG website.
User-Provided Control Circuitry ("Homebrew"): The RT-11's interface is designed for simplicity, allowing users to construct their own control circuits. For basic two-wire control, only DC power and ground are needed. The tuner will automatically execute a tuning cycle if RF is present at power-up. A momentary open switch on the +12 VDC power line can control the tuner by cycling power.

DB-9 Connector Pinout:

Pin 1: +12 volts DC @ 250mA (Power input).
Pin 2: Bypass mode select (Momentarily grounding bypasses the tuner).
Pin 3: Tune mode select (Momentarily grounding while RF is present starts tuning. Also used for Icom/Alinco interfaces).
Pin 4: Auto/Semi mode select (Momentarily grounding sets to automatic mode. Default is semiautomatic).
Pin 5: Tune LED (Connects to ground for a red LED, lights during tuning).
Pin 6: 1.5 LED (Connects to ground for a green LED, indicates SWR status and mode).
Pin 7: Radio Out (Used only for direct Icom or Alinco control).
Pin 8: Ground.
Pin 9: Ground. Control functions are activated by grounding the relevant control pin to Pins 8 or 9. LED anodes connect to Pins 5 or 6, with cathodes to ground.

Operating Modes:

Semiautomatic Mode (Default): Tuning begins only when Pin 3 is momentarily grounded.
Automatic Mode: Tuning begins automatically whenever SWR exceeds 3:1 during transmission. Can be set by momentarily grounding Pin 4.
Bypass Mode: Momentarily grounding Pin 2 bypasses the tuner, sending RF directly to the antenna without matching.

Power Level Considerations:

The RT-11 is rated for 125 watts peak power. Exceeding this limit, especially with amplifiers, can damage the tuner. Users must ensure their transmitters or transceivers do not exceed this limit for CW and SSB operation (50% duty cycle). Foldback Circuits: Many modern solid-state radios have automatic foldback circuits that reduce power when SWR is high, protecting the RF amplifier. If a radio lacks a foldback circuit (common in older radios, tube radios, solid-state amplifiers, and Ten-Tec transceivers), tuning power must not exceed 25 watts to prevent tuner damage.

Maintenance Features:

The RT-11 tuner is largely maintenance-free and designed for rugged outdoor use. The outer case can be cleaned with a soft, damp cloth. Avoid temperature extremes, water, impact, or static discharge.

Warranty and Service:

Factory-assembled units come with a one-year warranty against defects in parts or workmanship for the original purchaser. Kits are warranted for parts only for one year. A copy of the purchase receipt is required for warranty service. All returns must be shipped pre-paid. Repair turnaround time typically ranges from 2 to 6 weeks. LDG also offers post-warranty service, with repair charges communicated beforehand.

Firmware Upgrades:

LDG may release upgraded firmware to refine operation or add features. The RT-11 is not field-programmable, requiring the user to remove the existing 68HC11 (U1) chip and replace it with an upgrade chip. A PLCC extraction tool is ideal, but a substitute can be fashioned from a paperclip. The old processor chip must be returned to LDG as upgrades are sold by exchange to minimize costs (typically $10-20).

Technical Support and Feedback:

Technical support is available via phone (410-586-2177) weekdays from 9 am to 5 pm Eastern time, fax (410-586-8475), and email (Idg@Idgelectronics.com). LDG encourages users to provide feedback on software or hardware improvements, offering a free upgrade if an idea is incorporated. They also welcome user testimonials and photographs of the RT-11 in use for their website.