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Simple HF ATU on Lengths of Coaxial Cable

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ANTENTOP- 01- 2014 # 018

Simple HF ATU on Lengths

of Coaxial Cable



However, 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.


On my 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.


For 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.

Of course, 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 ATU.


At the 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.



Figure 3 Connection of the Simple HF ATU on lengths of Coaxial Cable

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Last Updated:

January 7, 2020 22:37