2m Tape Yagi
WB2HOL 3 ELE YAGI
The WB2HOL yagi is a popular choice for ARDF. A link to the original design can be found at the end of this post.
This page describes a construction methods for a stand-alone antenna where the receiver is connected by a coax feed.
Alternatives for a collapsible and integrated antenna+receiver unit are described in a separate post.
ALTERNATIVE CONSTRUCTION
The WB2HOL yagi uses 4-way pipe connectors used to support the elements, but these are not generally available in the UK.
The alternative was to use 2-hole plastic saddle clips, made to fix a plastic 21.5mm overflow pipe, which forms the antenna boom.
The elements are made from 25mm wide tape.
The basic dimensions are shown below, optimized for operation at 144.5MHz
FIXING THE SADDLE CLIP
A 4mm bolt through a drilled hole in the bottom of the boom and clip. If the saddle is not positioned near a cut end of the boom then provide an 8mm hole in the top of boom to allow a nut to be dropped over the bolt. A centre drill produces a nice clean cut in the plastic pipe, for these larger diameter holes.
FORMING HOLES IN THE TAPE ELEMENTS
Two 4mm holes are required required in the tape elements to align with the saddle clip holes. Drilling with a standard wood bit will almost certainly rip the tape to pieces, and produce potentially dangerous flying debris, so is not a good option.
Instead, make a small hole with a sharp point (eg bradawl or nail ) and ease the hole out with a larger diameter tool to 4mm - then clean off any swarf.
An eyelet punch works well for this application.
SUPPORTING THE TAPE ELEMENTS
A yoke is bolted between the saddle and the tape element to provide the main support to the tape elements. A yoke length of 100-125mm for the reflector and director elements is suggested with a longer length for the driven element. In the photos below a length of 25mm wide box conduit (top only).The profile nicely supports the curve of the tape element. Alternatively the yoke can be cut from a length of plastic pipe, or from something else to hand.
The inclusion of a top-yoke will provide additional stiffness. A 100m length will suffice. The photos below show a top yoke cut from 21.5mm plastic pipe.
yoke bottom view
end view of yoke
with top stiffener
DRIVEN ELEMENT
The gap between the driven element halves is 10mm.
Take the paint off the underside inside corners of the driven element halves and tin.
Form the hairpin match from stiff wire around some 22mm pipe.
The Wire length is 100mm plus 10mm each end for the solder legs (120mm total).
nb. in this example a small diameter tube is used for a yoke stiffener.
The Velcro is used for folding the tape elements for easier storage or transportation. The element are end-capped with Velco.
Because each element half has only one bolt fixing some means of preventing it rotating is required.
for example :- A small double sided adhesive pad between the tape element and the supporting yoke.
BALUN
Not everyone has found the need for a balun, but if you do, 7 turns of the coax feed wound round the boom does the trick.
tip.
Longitudinal alignment of holes drilled in the pipe boom is essential. A length of aluminium L-section will cradle the plastic tube and provide a straight edge for a pencil score line.
links
Unfortunately the link to the original web article seems to have been deleted but Goggle ‘WB2HOL yagi’ and you will get hundreds of returns.