Symmetrical (and asymmetrical) remote-controlled and affordable kilowatt KW antenna tuner

this board contains the switching transistors for the bistable relays. All outputs have reverse current diodes as well as an HF filter capacitor and a 10 ohm resistor to relieve the mosfets from surge currents.

The Mosfets are controlled by an Atmel microcontroller with port expansion using three shift registers.

The controller only has one task: reading a command from the serial interface and switching the corresponding relay. Example:

L11 … switch on coil 1

L20 … switch off coil 2

C51 … switch on capacitor 5

C70 … switch capacitor 7 off

H1 … switch the capacitors to the output (H = rear)

V1 … switch the capacitors to the input (V = front)

These commands can be sent with any serial terminal program, or with software, or with self-made programs.

The serial interface is PC compatible (+/- 12V) and has the parameters: 9600Bd, 8 data bits, 1 stop bit, no parity

A horizontal loop with a circumference of 90m was hung as a pentagon and connected to this tuner by means of a 25m chicken ladder. In addition, about 250pF and about 4uH each were switched to adapt the 40m band. The residual SWR was measured to be 1: 1.08.

A WSPR transmitter / receiver with 5W was then connected to this antenna. After a few days of operation, this arrangement achieved the world's top position for 2-way spots on 40m, with a good gap to second place.

Of course, this performance is mainly due to the antenna, but it shows that the tuner works with very little loss and makes a decent adjustment.