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ANTENTOP- 01- 2004, # 005  

Something about ATU





Classical Matching Unit with taps


You can see that C3 is isolated from metal cabinet of the ATU. It is not convenient for practical design of an ATU, so amateurs often use Classical Matching Unit with taps. 



Fig. 4 shows such MU with asymmetrical output, Fig. 5 shows Classical Matching Unit with taps with symmetrical output. These schemes (Fig. 4 and 5) cannot give such careful matching, as shown in Fig. 2 or Fig. 3 have provided. But in case if it is need to minimize dimensions of an ATU the schemes can be used.


Multi-range Matching Unit with taps


So, if you want to build an ATU having minimum sizes and parts try the schematic shown in Fig. 6. However, the Matching Unit   has not high efficiency at upper amateur ranges because of lowering of the Q-factor of L2 and because of not optimal selection of taps from L2. But usage of such simplified multi- range Matching Unit   at amateur HF - ranges 1,8- 10-MHz is quite acceptable.


T - Matching Unit


Classical Matching Unit is very effective in the work. However, among radio amateurs and military T- Matching Unit has more popularity then one shown in Fig. 2.  It takes place because T- Matching Unit have high efficiency at very wide frequency ranges and T- Matching Unit allows to do easy automatic tuning (that very likely to the military!). Also, T- Matching Unit works very well with for asymmetrical coaxial cables feeding modern antennas.  Fig. 7 shows schematic of T- Matching Unit. The MU has rather good parameters. It is possible to do matching a 50–Ohms transmitter to 10- 1000-Ohms antenna. It is possible overlap all HF- amateur bands from 3,5 up to 30 MHz using only one variable inductor at 0.5-30-μH and two variable capacitor at 10- 250-pF.  The MU does matching at 1.8-MHz if to bridge C1 and C2 to connect fixed capacitors at 200-pF.


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