Symetrical antenna tuner
The Balanced L-Network is the way to build a balanced antenna tuner. It has very low loss. The two roller inductors be tuned simultaneously. And to switch the variable capacitor from the input side to the output side. To match a larger impedance range, additional fixed capacitors switched in parallel to the variable capacitor. Current balun is used on the TX side of the antenna tuner to convert the 50 Ohms balanced impedance to unbalanced.
Antenna tuner schematic
For the construction of the antenna tuner I use a 20-1000 pF variable vacuum capacitor, two indent roller inductor 32uH and JK57HS56-2504-01 stepper motors. Switching realized by means of vacuum relays. Balun made on two rings type FT-240-43 using a wire with silver coating in teflon insulation.
Antenna tuner construktion
I use the steppertune controller for controlling the antenna tuner. Steppertune controller has been modified. I added dc-dc converter from 12 to 24 V. This voltage is needed to power the vacuum relays.
Modified steppertune controller
In dipoles with ladder line it is useful to check and observe the symmetry of the antenna. Even if one wire is torn off, the antenna tuner will tune the antenna, but we will not know that it is not working properly. To check the symmetry of currents in the ladder line I use the device that I built it myself. This is the current indicator in each wire of the ladder line. The device is a two-part probe and indicator.
Schematic diagram
Photo of the probe
Photo of the indicator.
