Here are the dimensions for the fold-up 2m yagi that I designed
several years ago.
The elements are made from #8 (3mm) aluminum wire. Radio Shack
sells a 40' (12m) roll of "ground wire" which will make 4 antennas.
I've also seen plastic covered solid aluminum wire sold for
clotheslines which is stiffer (but take the plastic insulation off of it
first.)
Reflector: 40" (101.6cm)
Driven element: 38.5" (97.8cm)
Director: 37.25" (94.6cm)
Spacing: 16" (41cm)
The boom is 40" (102cm) of nominal 1/2" PVC thinwall water pipe
(actually about 200mm OD). Drill holes through the pipe for each
element, starting near one end. (This leaves some room on the
other end for a handle.) Insert the elements through the holes, and
wrap a small piece of tape around each one above the boom to
keep it centered. If you color code the holes and ends of the
elements it is easier to assemble in a hurry, without worrying if you
got the right element in the right place.
To disassemble, slip the elements out of the holes and insert them
into the boom length wise. Put a pipe cap on each end, and you
are ready to go.
Feedline: I use a delta match with a pair of alligator clips to hook
the feedline to the driven element. Make a half wave coax balun
(using 32" or 81.3cm of foam coax, or 26.5" / 67.3cm of solid
dielectric coax). On each end of the balun, attach a 7" (18cm)
length of hookup wire with an alligator clip on the far end. These
clip to the driven element about 2" (5cm) each side of the boom.
Adjust the clip location for best SWR, then mark the element so you
can find the same point again.
If you aren't used to making a coax balun, it is simple. Strip back
the insulation and braid from a piece of coax so the remaining
length is as specified. Fold the coax in a loop and solder the two
ends of the braid together. The two ends of the center conductor
are the outputs of the balun. The feedline connects to either end
output of the balun and the common ground.
The resulting package is about 42" (107cm) long, which I find a bit
awkward for backpacking if there are any overhead branches.
I have experimented with hinging the elements by bending an eye
on the end and connecting them with a bolt. (Use a nut with a fiber
insert to keep the bolt from unscrewing as you work the elements.)
Arrange the joint so it acts as the stop to keep the element from
passing all the way through the boom. With this approach, you can
get the element lengths down to about 22" (56cm). I found that I
couldn't insert all 3 elements into one section of pipe because of
the size of the hinge joints, but it worked to put two in from one end
and one from the other end. The boom can then be made from two
nesting sizes of PVC with a reducing coupler to join them.
If you want more gain, you can try 5 elements:
Reflector: 39.5" (100.3cm)
Driver: 37.75" (95.9cm)
Director (3): 36.5" (92.7cm)
Spacing: 16" (41cm)
You will probably want to use two sections for the boom.
One last suggestion to try: the "string beam".
Use the same elements, but with string for the boom. Take two
strings and tie them together at one end. About 3' (1m) from the
end, tie the strings to the first element at about the 1/3 points on
the element. Continue with the other elements. It is convenient
to add a nice handle (PVC or wood?) tied to both strings behind
the reflector.
To use, tie the end of the strings to a convenient tree branch or
other support. Grab the handle and pull the strings taunt. The
yagi should snap into shape. Works great if you have a support
available for the front strings. (The longest antenna I've seen
built this way had over 40 elements and was over 60' / 20m long!)
Happy hiking! - Dale WB6BYU
PS: I still think the tape measure yagi is a better choice!