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.
of this allows simplify mechanical design of the ATU. Figure 1 shows schematic of the
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).
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
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
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.