Gents,
I enjoy reading the pros and cons of yagis vs quads every time it comes us
because there are always things that I forget about both. In May of last
year I designed a "prototype" 3 element quad for 20-17-15 on an 18 foot
boom. Actually, W4RNL has already done all of the modeling for me on his
website. He has modeled a quad on an 18 foot boom that is 3 elements on
20-17-15 and 4 elements on 12 and 10. This is exactly what mine is. I
originally designed it for an experiment which means it was to be temporary,
maybe up in the air only a month. I used a 2X4 for the inner boom support
(abt 8 ft long). Then I added some aluminum to each end to extend it out to
18 feet. I then added the 12 (20-15) spreaders. 8 were commercial fiberglass
from an old Cubex quad and the other 4 were a combo of Schedule 20 PVC and
aluminum tubing. For the wire I chose Radio Shack TV rotor cable. The stuff
that comes in 100 foot lengths that has five conductors for only around $10.
I then seperated the wires and now had 5 100 foot lengths of wire of around
number 20 gauge. Trust me, it handles legal limit with ease.
I then assembled the thing. I later added 12 and 10 on a seperate feedline
(common to 12 and 10 though). Used seperate driven element for these bands
and a second set of directors.
All in all my "junk yard special" quad cost me under $100 to build. Will it
survive the winds of Virginia or New Hampshire? Surely it will not but I
live in very temporate San Diego AND it is on a 33 foot crank up tower that
I can crank down if I know the wx is getting crappy. In August I
"re-enforced" the original wood and aluminum boom combo by installing a
second boom directly in parallel with the first. It is two 10 foot lengths
of radio shack tv mast.
This thing is a flame thrower and I can say three things:
1. It is computer optimized thanks to W4RNL (except I used number 20 ga.
wire which does not seem to bother it at all).
2. I built it myself.
3. It kicks butt.
I also learned a lot in the process. Is it any better than something like
the TH7 or the new KT-36 or the big F-12 yagis? Probably not really but it
sure was fun to do and the guys on the air get a good laugh when I tell them
abt the construction of the junk yard quad.
Lane
Ku7i
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