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255MHz 5 ELEMENT YAGI-UDA ANTENNA

5 Element Yagi-Uda antenna for 250MHz to 260MHz . September 2022


Investigating a practical and easily Yagi-Uda antenna construction technique for VHF and UHF and also keen to have a listen to the known pirate activity on a United States Navy communication satellite a small 5 element Yagi-Uda antenna for 255MHz was chosen.

The goal was to develop an element mounting technique that allowed easy installation and replacement of the elements, allow for easy adjustment of the element attachment point on the boom while requiring no drilling of holes into the boom. Also when the antenna is no longer required it can be easily recycled into another antenna.

 

Photo 1 255MHz Yagi mounted on repurposed tripod.

 

Construction

The element mounting assemble shown in Figure 1 and Photo 2 & 3 consists of a stainless steel hose clamp with 5mm stud hole drilled in the strap and counter sunk headed set screw mounted with the flat head against the boom as shown in Photo 4. The hose clamp stud mount requires no holes be drilled into the boom and allows for infinite lateral adjustment along the boom.

The element mounting bracket shown in Photo 5 is fabricated from 15 x 15mm aluminium channel pop riveted to the element mounting plate. The aluminium channel is notched out so that it mount flat against the boom and clear of the hose clamp strap.

Photo 6 shows the Completed 255MHz Yagi-Uda antenna.

 

  Figure 1 Element to Boom mounting arrangment..

 

  Photo 2 Element to Boom mounting assembly.

 

  Photo 3 Element to Boom mounting assembly.

 

  Photo 4 Stainless steel hose clamp and counter sunk headed set screw.

 

  Photo 5 Element mounting bracket.

 

  Photo 6 Completed Yagi-Uda antenna assembly.

 

Antenna details

Frequency:                         255 MHz, (useful from 249.9 to 260.1 MHz)

Wavelength:                      1176 mm

Rod Diameter:                   10 mm

Boom Diameter:                20 mm

Boom Length:                    855 mm

Elements:                          5

Gain:                                 7.99 dBd (approx.)

 

Element

Length (mm)

Position (mm)

Note

Reflector

574

0

 

Dipole

See details

282

 

Director 1

541

371

Distance Dipole - Director 1: 88 mm

Director 2

536

582

Distance Director 1 - Director 2: 212 mm

Director 3

532

835

Distance Director 2 - Director 3: 253 mm

 

 

Balanced Dipole

Dipole, straight

Diameter

10mm

Half Wavelength

587.85mm

Length A

281.5mm

Reduction

0.958

 

 

 

Yagi-Uda antenna dimension calculator

https://www.changpuak.ch/electronics/yagi_uda_antenna.php

JavaScript Version 12.01.2014, based on Rothammel / DL6WU

 

Driven element and matching notes.

http://dg7ybn.de/Symmetrising/Symmetrising.htm 

 

 

Video of the 255MHz Yagi antenna features and operation.

 

 

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Page last revised 26 October, 2022
 

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