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
Photo 1 255MHz
Yagi mounted on repurposed tripod.
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 bracketshown in Photo 5 is
fabricated from 12 x 12mm 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.
6 shows the Completed255MHz
to Boom mounting arrangement..
Photo 2 Element to Boom
Photo 3 Element to Boom mounting
Photo 4 Stainless steelhose clamp and counter
sunk headed set screw.
Photo 5 Element mounting bracket.
Photo 6 CompletedYagi-Uda
Frequency:255 MHz, (useful from 249.9 to 260.1 MHz)
Rod Diameter:10 mm
Boom Diameter:20 mm
Boom Length:855 mm
(Based Yagi antenna calculator)
Distance Reflector - Dipole: 282 mm
Distance Dipole - Director 1: 88 mm
Distance Director 1 - Director 2: 212 mm
Distance Director 2 - Director 3: 253 mm
The dipole was modelled withYagi
Uda Antenna Calculator and based on 10mm diameter aluminium tube.
The over all reduction factor of 0.958 is a result of the 10mm
dipole element diameter and will be different for other tube
diameters. The reduction factor is applied to the
calculated half wavelength of 255MHz to given overall dipole element
length of 563mm less the gap of 10mm resulting in the A element lengths
The 1:1 transformer was in this
instant four toroidal core over the 50ohm coax near the feed point.