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Outdoor Window Mounted HF Helical Antennas

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ANTENTOP- 01- 2020, # 024

Outdoor Window Mounted HF Helical Antennas

 

 

The antenna was mounted on the clothes drier installed near wooden window frame and was placed near 100 cm out of the concrete wall of the building. Form of the antenna was made from wooden sticks. The sticks were fixed by the nails to the wooden triangles.

 

Each side of the wooden tringle had diagonal of 70- cm. Length of the sticks was 2.3- meter. Aluminum stick was installed on the wall of the building on the old antenna insulator from VHF radio. I used chip bare aluminum wire in diameter of 2- mm. For me it was very convenient to use the bare aluminum wire because it was possible very easy to connect to the wire to find resonance of the antenna on the desired bands. Table 1 shows length of the helix where the helical antenna has resonance at the amateur bands.

 

 

 

Table 1 Length of the Helix where the Helical Antenna Has Resonance

 

Band, m

 

Helix with Length 45 meter

Helix with Length 22 meter

Length of the Helix, m

Harmonic Frequency of the Helical Antenna

 

Length of the Helix, m

Harmonic Frequency of the Helical Antenna

 

80

45

1

-

-

40

44

2

22

1

30

35

2

17

1

20

-

-

20

2

17

-

-

18

2

 

 

When the helical antenna with grounding is installed and coaxial cable (do not forget about RF chokes on the both sides of the cable) is placed from the antenna to the transceiver, the helical antenna should be tuned to the resonance on the desired bands. It is very simple to find the resonance frequency of the antenna with help of RF-bridge. By choosing the tap from the antenna find the resonance frequency of the antenna. Device Artificial Ground helps eliminate the antenna reactance. So, it is needs two steps- first choose the tap, then, mark the tuning on the device Artificial Ground where the helical antenna has exactly resonance.

 

It is possible straight away connect to the taps shown in the Table 1 and then tune the antenna in the resonance with help of shortening capacitor or lengthening inductor. If the helical antenna has the resonance lower the desired frequency in serial with the antenna turn on a shortening capacitor, if the helical antenna has the resonance higher the desired frequency in serial with the antenna turn on a lengthening inductor.

However, helical antenna tuned to the resonance with help of a shortening capacitor or lengthening inductor has narrow passband compare to antenna tuning by choosing tap.

 

The helical antenna is sensitive to position of the counterpoises and coaxial cable going from antenna to transceiver. So after tuning the antenna the things should be unchangeable in the place.

 

Antenna was installed at the first floor of the 9- story building. Antenna was tested in the Air and showed good result. However, I used the antenna (second variant, with helix in 22- meter length) only one month. Then the antenna was demolished because it was too bulky and prevent from drying the clothes (and curiosity of my neighbors)...

 

References

 

1. http://www.antentop.org/qrp.htm

 

2. http://www.antentop.org/024/ZS1JHG_024.htm

 

 

73! de VA3ZNW

 

 

 

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Last Updated:

January 30, 2021 18:47

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