ATU-LP/ATU-HP 250W/2000W (NDB) & 375W/3000W (DGPS)

Vector Series NDB/DGPS Antenna Tuning Units

Since introducing the world’s first totally solid-state, high power radio beacon in 1970, Nautel has supplied the highest quality and reliability in non-directional radio beacons.

The most recent Vector Series Transmitters and Antenna Tuning Units continue this heritage and provide a dramatic improvement in system coverage.

Note: ATU-LP is shown with optional sunshield.


The Nautel Vector System offers a unique, patented solution to maintain system coverage regardless of undesirable antenna effects such as salt build-up on antenna insulators and ground plane resistance changes.

Highlights include:

  • Constant field strength output for higher system availability.
  • Automatic antenna capacitance tuning using dual astatically wound loading coils.
  • Automatic resistance matching for higher system availability.
  • Optional adjustable series resistor optimizes the tradeoff between antenna efficiency and bandwidth.
  • Remote control and monitoring of the ATU to limit worker exposure to strong RF fields, in keeping with Safety Code 6 / IEEE C95.1-1999.
  • Compliant with the specifications and recommendations of ICAO Annex 10, Vol. 1, Part 1, Section 3.4.
  • ATU cabinet enclosures designed for use in all types of outdoor environments including tropical, desert, coastal areas and offshore installations.
Constant Field Strength Output for Higher System Availability

The Vector transmitter and ATU-LP/HP communicate via a serial data bus that allows the transmitter to monitor the antenna current.

The transmitter can automatically (user enabled feature) adjust its output power to maintain a constant antenna current, thereby maintaining constant field strength of the radiated signal.

This feature is unique to Nautel NDB and DGPS systems.

Automatic Antenna Capacitance Tuning Using Dual Astatically Wound Loading Coils

The capacitive portion of the antenna impedance is automatically matched using dual astatically wound loading coils.

The loading coils are designed to be low-loss to maximize antenna efficiency.

The dual astatic pair has a lower field than a single coil solution and this reduces eddy currents induced in the ATU enclosure.

Automatic Resistance Matching for Higher System Availability

The ATU not only automatically matches the capacitive portion of the antenna impedance using dual astatically wound loading coils but also automatically matches a +/-2:1 (4:1 overall) change in the resistive portion of the antenna impedance.

This feature virtually eliminates seasonal visits to NDB and DGPS sites to re-tap the traditional fixed-tapped matching transformers and is unique to Nautel ATUs.

Optional Adjustable Series Resistor Optimizes the Tradeoff Between Antenna Efficiency and Bandwidth

High ‘Q’ antenna systems, with narrow bandwidth, can cause undesirable sideband attenuation.

The optional series resistor bank, with integral sun shield, allows for the insertion of resistance in series with the antenna to reduce the ‘Q’ of the antenna system and thereby increase the bandwidth of high ‘Q’ antenna systems.

Remote Control & Monitoring of the ATU to Limit Worker Exposure to Strong RF Fields

The ATU may also be controlled and monitored via the GUI to limit the operator’s exposure to the strong RF field of the antenna in keeping with Safety Code 6 / IEEE C95.1-1999.

Remote control and monitoring of the NDB and DGPS transmitter, and ATU is available via the optional VR-Link remote control and monitoring system.

After extensive research into the most common antenna-related field issues, the ATU-LP and ATU-HP automatic antenna tuning units were developed to:


  • provide industry-leading, state-of-the-art antenna impedance matching to the associated Vector NDB transmitters under all weather conditions
  • mitigate the effects of seasonal ground conductivity variations and the build-up of salt and other environmental contaminants on antenna insulators
  • provide a constant and stable coverage when used in conjunction with Vector NDB transmitters
Development, Testing & Functionality

Learn more about the development, testing and functionality of the ATU-LP and ATU-HP automatic antenna tuning units in this white paper Engineering the All Weather Antenna Tuning Unit (ATU)