Constructing a 23cm Yagi antenna
First, think a bit:
1. What frequency should it be used for?
2. What gain should it have, how long is the boom?
3. What kind of material do I have (can I get)?
4. Indoor, portable or outdor use, mechanical properties
If you know what you want, download this excel sheet
(by VK3AUU and VK3AKI), start it and put the values in.
As an example I built a short 13 element Yagi using
one meter long 15 x 15 mm square Aluminum boom,
elements are 4 mm hard aluminum wire.
Cut elements according to the software results. Accuracy
should be within 0.1 mm. Phase the edge at one side of the
elements. Drill holes in the boom, first 3.8 mm then 4 mm.
Hammer elements thru the boom, phased side ahead.
Elements must fit tight and must have and keep
good electrical contact to the boom!
Reflector can be made from the same wire as the elements.
To improve f/b I use perforated sheet (see picture below).
The reflector is mounted to the boom using small brackets
cut from 90° aluminum profile.
Radiator is made from 3 mm copper wire. Wire diameter is
not critical, large diameter = more broadband, small diameter =
easier to bend.
To match the 200 Ohm (symmetric) radiator to 50 Ohm
(unsymmetric) coax a 4:1 Balun is required. It could be
made from coax cable cut to one half wavelenght (l) and
bent to a loop.
Do not squeeze the cable during bending, the diameter
ratio of inner and outer conducter must be maintained.
1278 MHz, UT85 semi-rigid, v = 0.695
Simulations with MMANA
I did some simulations with MMANA software.
You may download the file here (shift-leftclick)
Simulation seemed to proof what was promised from the Excel spreadsheet.
Measurement will be done later.
yet to come.....