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ANTENTOP- 01- 2017 # 021

Several Universal ATUs for the Whole Amateur HF Band



If one wants to operate with a symmetrical two wires feed line then it will be wise to use a two isolation section variable capacitor on the ATU output as is shown in Figure 11.

The capacitor allows compensate reactance in the two wires line. However the capacitor is hard to find part and the installation is nice but not necessary…




Figure 11 Universal ATU with Symmetrical Output for Two Wires Open Line



Simple all HF Band matching device The Universal ATU that is described hereinabove is simple but has lots parts and sometimes is not so obviously in tuning. However it is possible make a simple all band ATU that is clear in tuning and has small quantity of parts. The schematic of simple ATU is shown in Figure 12. However the simple ATU is not so effective on the high HF bands (compare to the previous ones). As can be seen from the diagram, this ATU is a conventional LC-tuned tank. With switch S3 and capacitor C1, it can be tuned on frequency of any selected amateur band. Switch S1 allows adjustable coupling with the transmitter’s final stage. S2 provides the variable coupling to the antenna. By using S1, S2, S3, one may match just about any transmitter’s final amplifier to any antenna. The matching network works well in the HF range from 1.8 to 30 MHz with nearly all antennas. But, I should repeat, in the higher ranges above 14 MHz to 32 MHz, the efficiency is low. 


For the coil form for L1, I used a glass jar (it was empty jar from mustard) with an OD of 55 mm and a metal screw-on lid.  

L1 consists of 30 turns of copper wire with a diameter of 1.5 mm, (#14AWG). The coil was wound over a 50-mm length on the jar. The first and last turns were held in place by using automobile epoxy. The first, second, and third taps were placed at 2, 3 and 4 turns. Then the next turns 3, 4, and 5 were placed at 6, 8 and 10 turns. Taps 6 and 7 are at 13 and 15 turns. Then the turns are uniform for four turns. Then, tap 8 is at 19 turns, tap 9 at 23 turns, tap 10 is at turn 27 and tap 11 is at end of the coil- 30s turn. Capacitor C1 is a two section air variable capacitor from an old tube broadcast receiver. Such kind of capacitor may be used at power up to 100 watts going to this ATU. The ATU also improves reception because selectivity of the LC- circuit.

 To tune the ATU, an LED D1 is used. The ATU is tuned for maximum brilliance from the LED. The LED is located in the winding of the current transformer T1. The current transformer is wound on a ceramic ring with the OD of 22 mm. I used a ceramic ring from an old tube socket. All the leads and center metal clamp was removed. Another type of ring (ceramic, plastic or ferrite) for the current transformer may be used everything is depend on the scratch box and experience of amateur.

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Last Updated:

December 17, 2017 14:04