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  LF / VLF Antenna Tuning Units  
 

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LF / VLF Antenna Tuning Units

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 left. 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.

 

ATUs 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. The next photo shows a CEC motor package made for the variometers to provide fine positioning control and position readback. 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

The T-network shown at left, is for a small 50 kW transmitter. It uses small copper tubing coils as well as CEC Gas Capacitors. The network matches the impedance from the loading coil to the output impedance of the transmitter. An arc gap mounted above the capacitors provides voltage protection for the capacitors. CEC manufactures arc protection systems to detect arcs in the gaps pictured above. These systems function to remove transmitter RF energy so as to limited energy in an arc.



CEC makes VLF/LF ATUs from 50 kW to 2 MW

All ATUs comprise CEC designed and manufactured high voltage and high current components. This picture is from a 2 MW VLF ATU. Note the size of the people for scale!

Click here to see many of our LF/VLF Installations.

 

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