ANTENTOP- 01- 2013 # 017

Helical Antenna for the 20- meter Band

Capacitor C1 has capacity 510- pF. I used a mica capacitor. Inductor L1 has inductance 0.21- uH. It contains 5.5- turns of bare strand copper wire (18- AWG) air coiled on a form with diameter 12-mm. Gap between turns is 1- mm. ATU is tuned by stretching- squeezing of the inductor. Antenna has SWR 1.0: 1.0 at 14.100- Khz. At the 14.000- kHz SWR was 1.2:1.0. At 14.450- kHz SWR was 2.0:1.0.

The ATU made inside of a clear plastic box (Food Box). With the antenna the ATU (item 9) is connected with help of M-M adaptor (item 7). Coaxial cable (item 11) is connected to the ATU. Copper strip (item 10) was attached to the RF- connector of the coaxial cable with help of a clamp. The strip was connected to the antenna grounding system. Antenna is fed through buried coaxial cable (BFLEX, DAVIS- RF is supplier). The coaxial cable then is going through a ventilation hole in to the basement where my shack is placed.

Antenna works fine at the 20- meter Band. However, through some time I decided use to the antenna for other amateur bands.

At first the mostly effective solution was very clear for me. I need to install ATU made inside a big clear box with switch that could be match antenna at the used bands. The ATU circuits for should be similar to the 20- meter ATU. I have measured the antenna impedance at the other bands. New parts for other bands were calculated. Old ATU was removed for the modification and the antenna was fed directly by the coaxial cable. Temporary fed as I thought... But other deals distracted me from doing of the universal ATU... Then autumn and winter is coming...

So, the universal ATU still does not made. However, I discovered that the antenna works good at the 10-, 15-, 20-, 30-, 40- meter Bands with help just ATU between my transceiver and the coaxial cable going to the antenna. My MFJ VERSA TUNER II could match the antenna on the bands. Another one tuner, LDG Z- 11 PRO II also could match the antenna on the bands. Be truth my door on to backyard is frozen at the cold winter. So I could not go outside most of the cold days (as I planned to switch the bands). So, the direct feeding is preferable for me at the situation. But may be at the coming summer I will do the universal tuner...

73! de va3znw

Figure 2 Schematic (A) and Design (B) of the Helical Antenna ATU

Helical Antenna for the 20- meter Band

Winter Time.

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