Some 1296 MHz gear
folded dipole template & coax mitre



folded dipole template



folded dipole photo





Small mm changes in lengths and dimensions of antenna elements can have very significant performance effects on 1296 MHz.
Here I have made two templates (ca. 99 and 110 mm tip to tip lengths) so you can build reproducible folded dipoles.
The templates include two circular bend points, so the wire can be correctly and evenly shaped.
Also a central 'break' point creates the correct end spacing, so that one end of the folded dipole will be correctly positioned
to go straight on the antenna socket, and the other end will be slightly offset to go to the second point of the 4:1 balun.

NOTE: see links at the bottom of this page for the 3D printing files.

The 4:1 balun was made using a halfwave long coax line, I used RG402 semi rigid coax.
The solid copper tube on the outside of RG402 is very much easier to handle (when soldering all the commons together)
than trying to work with tiny bits of soldered braid when using screened coax.
To simplify and ease cutting and manipulating the semi rigid coax I made up a simple 3D printed mitre jig.
In practice cut a 100 mm piece of the coax, measure out the central 80mm (10mm at each end) and use the mitre to cut the 10 mm tubes off.
We keep the centre silver plated wires at each end to wire up the balun (trim them as appropriate).
The halfwave line is carefully bent around so the ends are side by side.
At 1296 MHz this is just possible within the bending range for the coax.

Folded dipoles
The table below shows folded dipoles used by a few authors on their yagi antennas.
You can see there is a range between them - ca. 99 mm to 110 mm tip to tip length.
I found the 99 mm template worked best (1 mm un enamelled copper wire) for my yagi designs.
Compared to other antennas, that feed directly into 50 ohm (e.g. Quagi, gamma matched yagi etc.),
the folded dipole arrangment seems to be very 'forgiving' ...
... perhaps the 4:1 balun also 'divides errors' by a factor of four too, making the matching less critical ? :-)


Yagi type dipole length
(mm) 		folded dipole length
(mm) 		Reference
/ link
12 element
(insulating boom) 		108
110
(2mm thick)
23 mm dia bends 		VK1NAM
6 element
metal boom 		107
(3mm brass) 		113
(3mm brass) 		VK1NAM
17 element yagi
metal boom 		106 108
(12 gauge wire)
236 mm total length 		W6PQL
folded dipole calculator - 98.9
(1mm thick)
213 mm total length
13.6 mm dia bends 		chang puak
calculator






semi rigid coax mitre



semi rigid coax mitre photo I





semi rigid coax mitre photo II





completed folded dipole photo



coax mitre
".stl" file
".scad" file
".gcode" file
 99 mm folded dipole template
".stl" file
".scad" file
".gcode" file
 110 mm folded dipole template
".stl" file
".scad" file
".gcode" file
 folded dipole from 23 ele yagi template
".stl" file
".scad" file
".gcode" file
 back to
3D page


THE CREATIVE SCIENCE CENTRE

Dr Jonathan Hare University of Sussex, Brighton.
e-mail: j.p.hare@sussex.ac.uk

home | diary | whats on | CSC summary | latest news