US4LEB ATU for HF- Bands

US4LEB ATU for HF- Bands

By: Sergei Klimenko, US4LEB

The ATU is used T-circuit for matching transceiver output with antenna. However, the features of the ATU is a Ball variometer and RF-Relays . The variometer is the variable inductor of the ATU. Using the Ball variometer allows to simplify the ATU design. RF relays switch on the coils of the variometer and it makes needed inductance.

All of this allows simplify mechanical design of the ATU. Figure 1 shows schematic of the ATU. Picture 1 shows the Ball Variometer used in the ATU. It was used a Ball Variometer from old military Russian Radio R-140. However it is possible use any ball variometer with maxima inductance of 30- micro Henry and with independent coils (that is not connected together in the design).

Relays K1 and K2 allow hook up the coils in bridge or in serial that depends on used HF band. On the 10- meter Band an additional coil L3 may be needed connected in bridge to the variometer coils.

The coil L3 is switched on with the relay K3. So, the combining of the L1, L2 and L3 allows find needed inductance for the ATU at the working band. Switch S1 does bypass antenna to the transmitter output.

Relay K4 connected RF transformer that provide symmetrical output. ATU was assembled in a metal cabinet. All connection wires from the coils to RF relays should have a minimal possible length. Variometer and L3 should be placed at distance at least 20- mm from the metal case. Capacitors C1 and C2 are mounted on an insulation plate.

Figure 1 Design of the US4LEB ATU for HF- Bands

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