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ANTENTOP- 01- 2004, # 005  

Something about ATU



By Igor Grigorov, RK3ZK



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.


So, 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.


As 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.


ATU Design


Fig. 1 shows schematic of a “classical” ATU. Such ATU has:


-        a 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 is done;

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