It is not difficult to build an Antenna Tuning Unit
(ATU) for any amateur HF band. Such device could be done with
usual coils and capacitors. However the real problem is making
a simple and effective ATU without lots switching and tuning that
could work over a broad range of frequencies. Below there are
given several different ATU that work effectively over all amateur
HF bands from 160-10 meters, easy to do and easy to tune and easy
to match antenna with transmitter. The ATU was tested with transmitters
having for working
50 and 75 Ohm output.
Figure 1 shows schematic of simple and universal
ATU that can capable of working on all amateur HF bands. Design
of the unit is based on ATU made by Peter Linsley
(G3PDL), Reference 1.
I repeat the schematic with some changes and found to be very
effective this one. This ATU is capable of matching the transmitter
final stage of 50-75 ohms output to an antenna load of 20 to 300
ohms in the frequency range of 1.8-32 MHz with an SWR of no higher
How it works:
In the 1.8 to 4-MHz range, the circuit consisting of L1, C2.1, and C2.2 is tuned
to resonance with the input signal. Capacitor C1 is used for fine-tuning
of the matching circuit with transmitter final.
7 to 32 MHz: For operation in the range of 7 to 30-MHz range, the
circuit consisting of the lower section “A”
of coil L1 and variable capacitor C2.3 is tuned to resonance
and the middle section “B” serves as a coupling coil for section
“A”. C1 also provides the fine matching with the final amplifier
stage. In the higher frequencies the upper part of the coil L1
acts as an RF choke and does not interfere with part “A” and “B”
sections of the coil.
For both ranges, the coupling coil L2 is a compromise
for coupling to the antenna. By adjusting C1 and C2, satisfactory
matching to the antenna can be achieved in both frequency bands.
This ATU does not cover the new amateur band at 5 MHz.
To use the ATU in the new band, a tap at 3.5 turns in section
“C” of coil L1 needs to be added as shown in Figure