you may rotate the S1 in receiving mode and tune on to maxima
reception. You need begin the tuning from the lowest length of
the length of the coaxial cable. Then turn on the next length
of the coaxial cable and check SWR.
memory it was very effectively ATU that could match lots of my
experimental antennas (be truth- antenna system- antenna plus
coaxial cable going to my transmitter) that I just connected to
the coaxial cable placed on the roof. One of the days I decided
to rework the ATU to get more efficiency. Any lover of the Smith
Chart and matching of the antenna by length of the transmission
line straight away could understand how the next ATU works. For
those, who do not care about the theory I include some simple
explanation. Figure 4
illustrates the explanation.
example, there is an antenna with impedance, let's say, 500 Ohm
and Reactance minus 100 Ohm. Line L3 transform the impedance,
let's say, to 200 Ohm and Reactance Plus 300-Ohm. Stub L2 kills
the reactance. The stub, depends on the length, may be opened
or closed. Then line L1 transform the pure 200- Ohm to 50-Ohm
at the transmitter terminal.
it is very simple explanation, in the real life, is required work
with the Smith Chart to find the gold length of the L1, L2 and
L3. I have a doubt that in real life somebody will do the theoretical
simulation at amateur station. But we may try it in practical
way. May be we would be lucky and maybe we can do it with our
design of our ATU we have all components that are at Figure 4. Line L3- it is coaxial
going from the antenna to the ATU. Line L1- it is variable length
of the coaxial cable that we connect between transmitter and antenna
system. Line L2- it is row of length of not used coaxial cables
that are sitting inside ATU. What can we do- just connect the
unused cable in to terminal ATU- antenna system. Then play! Chose
length from transmitter to antenna system, then connect the stub
and check SWR, and again try another connection to find the low
SWR at transmitter terminal. At first sight is hard to do but
having some experience (and maybe some theoretical base- GOOGLE
helps you) it is not so hard. Figure
5 shows schematic of the modified ATU. Pay attention
that Switch S2 has one empty position (physically I removed stopper
from the switch) when no one stub does not connected to the ATU.
Switch S2 was placed under switch S1.