ANTENTOP- 01- 2015 # 019

Symmetrical ATU

By: Vasily Perov, DL1BA (ex UK8BA)

Prototype of the tuner was made by VK5RG. The tuner was found by me at "Das DARC Antennenbuch" (Reference 1). However at the book there was given only brief description of the unit. The tuner takes my attention and by trial-and-error method I found the design (data for Inductors and Capacitors) of the tuner. Figure 1 shows schematic of the Symmetrical ATU. Pay attention that at the tuner the rotary switches S1-1 and S1- 2 do shortening of the unused turns.

The Symmetrical ATU is kind of usual two Pi- circuits, C1 is capacitor at hot end- capacitor that tune the inductor L2 to resonance and C2 is capacitor at cold end- capacitor that does matching for the load. Figure 2 shows design of the Symmetrical ATU.

All three inductors are placed in row. The inductors are wound by copper wire in 1.5- mm diameter (15- AWG). Inductor L1 contains 4 turns and placed between matching inductors L2-1 and L2-2. Inductors wound on a dielectric plate (PCB plate without foil) by dimensions 150x 80x 2mm. Two row holes were drilled in the plate. The rows were 50- mm apart and it was 3- mm distance between the holes.

At first step the inductors were being wound on to a form in 50- mm diameter. Then the dummy inductor was taken off from the form and inserted into the plate turn by turn. Inductor L1 contains 4 turns. Inductors L2- 1 and L2- 2 have 16 turns each.

Figure 1 Schematic of the Symmetrical ATU

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