What an ATU does?
You should not think
that an Antenna Tuning Unit (ATU) is a magic thing to do any antenna
work well with your transceiver. At installation between the transmitter
and feeder the ATU only does matching of output impedance of your
transmitter with input impedance of your antenna - feeder system.
It means that ATU allows to the transmitter with output of 50
Ohm to work normally with antenna plus feeder having any input
impedance. But probably SWR would be enough high in the feeder.
If the ATU is installed between antenna and feeder it does low
SWR in feeder and provides good operation for the transmitter.
But probably the antenna would work not in good way.
an ATU provides safe operation for transmitters end stage, if
the ATU is between the transmitter and the feeder, additionally
an ATU does low SWR in
feeder, if the ATU is installed
between antenna and feeder.
usual modern transceivers and military equipment have inner ATU
that does matching end stage with feeder or antenna. Below we take
close look to ATU design.
Fig. 1 shows schematic of a "classical" ATU. Such
Matching Unit, that provides the matching of end stage of the
transmitter with antenna - feeder system. Matching Unit is the
"heart" of any ATU;
A SWR mater or HF-bridge, that shows how the matching