ATU was made by me in far 80s. It was may be a simplest ATU what
I made ever. It contains only one rotary switch and rolls of a
coaxial cable. But the ATU works very well. The ATU has only one
lack- sizes. Sizes of the ATU are not small. Below there are several
words to the theoretical base of the ATU.
those who know the Smith Chart the principle of operation of the
ATU is not a secret. Using Smith Chart we can find how impedance
of antenna system is changed along a transmission line. Based
on this we can find optimal length of the transmission line and
place(s) on transmission line where we can install stub(s) to
eliminate the reactance in the line. Of course, the description
is too simple and GOOGLE helps those who want to know more about
Smith Chart and how we could match antenna impedance with our
transmitter using only transmission line of definitely length
described here matching unit it means: let’s turn on our antenna
through line with variable length and find when SWR at our transmitter
would be best. It is easy. It is simple. It works in most cases.
at some cases the ATU does not work or work not good but only
in some cases… Figure 1
shows schematic of the ATU.
ATU contains 11 lengths of 50-Ohm coaxial cable. First length
is 1 meter long, second one is 2 meter long, third one is 3 meter
long, and so on, next one has length in 1 meter longer the previously
one. The lengths of coaxial cable are connected to a four-pole
11-position rotary switch S1. So with help of the S1 you may choose
the length of the transmission line from transmitter to antenna
system. And if you are lucky (you will be lucky!) match the transmitter
with existing antenna system. The matching device works fine at
HF- Range 3.5- 30.0- MHz.
wish use the device only at 7.0- 30.0- MHz the lengths of the
coaxial cable should have step 0.5- m. First one should have 0.5-
m length, the second 1.0- meter length, the third one 1.5- meter
length and so on. Figure 2
shows the design of the ATU.