Continental Electronics provides Antenna Tuning Units (ATUs) for all types of antennas used in VLF and LF transmitting applications.

The ATU will commonly have a Helix Coil to provide bulk inductance for antenna tuning. RF current to the antenna exits the ATU through a bushing, as shown at right. An antenna grounding switch shorts the antenna for personnel protection while working in the ATU. A helix coil provides bulk inductance for tuning antenna capacitance. A typical small helix coil is shown here. It has a high voltage grading corona ring at top. A protective gap, shown at left, provides protection from lightning induced transients. The helix coil shown here is rated for 250 kVrms continuous. These ATUs utilize Litz (Litzendraht) wire for RF current ratings of tens to thousands of amperes. This special wire is formed by specially weaving many fine insulated wires into a cable. The ATU is typically metal lined to contain RF fields induced in the walls from the tuning inductors.

The ATU will have one or more variable inductors (variometers)

for tuning and loading control.

Variometers, such as the one at left, provide continuous fine adjustment of inductance. CEC makes motor packages for the variometers to provide fine positioning control and position readback, as shown at right. Typically one variometer provides tuning control for the antenna. This is connected in series with the helix coil. A second variometer provides loading control to match antenna resistance.

The ATU may have "T" networks to match transmitter output impedance.

CEC makes VLF/LF ATUs from 50 kW to 2 MW, using CEC designed and manufactured high voltage and high current components. The picture below is from a 2 MW VLF ATU. Note the size of the people for scale!