ANTENTOP- 01- 2017 # 021

Several Universal ATUs for the Whole Amateur HF Band

Figure 2

Universal ATU Covers 5- MHz Band

The effectiveness of this ATU mostly depends on the quality of parts and proper design. This is a resonant ATU and, therefore, on coil L1 and capacitor C2 there is a high RF voltage during the transmission time. These components must be of a high quality due to the high voltage present otherwise you have got burnet stuff inside ATU box...

The coil L1 is wound on a form with an OD of 55 mm. Each winding consists of:

1. Section A: 7 turns covering 40 mm length section of the coil form

2. Section B: 3 turns covering 15 mm length section of the coil form

3. Section C: 7 turns covering 30 mm length section of the coil form

Fig. 3

Design of L1 and L2

The coil form must be of a high quality material, RF ceramic will do the job. The wire used for L1 should be no less than 1-mm diameter (#18 AWG). The winding L2 is four turns and it is wound in the middle part of L1 and covers 40 mm. L2 can be wound using either stranded wire or solid wire with a diameter of 1.5-2 mm (#17-#12 AWG). Insulation tape with high- voltage capability should be used between L1 and L2. Figure 3 shows design of the coils.

Next step to improve the ATU was my attempt to build an ATU that could match load (in this case antenna) with reactive component, particularly if the reactive component was no more the value of the active component of the load. C3 was added to this ATU to compensate the reactive component of the load (antenna). The diagram of this modified ATU is shown in Figure 4. For the entire frequency Band from 1.8 to 32 MHz, the addition of C3 allows the SWR to be no worse than 1.5:1 with an antenna having such above mentioned reactive component. SWR of 1.2:1 in the HF Band from 1.8-7 MHz can be achieved if antenna has any resistive component of 20-300 ohms and has no reactance or little one.

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