It was designed and optimized using 144.250mhz as the center
frequency which is in the middle of the SSB portion of the 2 meter band
and according to the program has a gain of 11.68dBi with a front to back
(F/B) ratio of 37.44dB on a boom length of 8.68 feet with 1/4 inch
elements using a standard direct feed dipole insulated from the boom as
the driven element with a 3dB beamwidth of aprox 48.7 degrees..
No
matching device should be required but due to variations in your
construction practices, some trimming of driven element may be needed or
us a gamma match with non-split (not insulated from boom) solid dipole
driven element for best SWR.
When checking SWR, place antenna with
reflector on the ground and prop yagi straight up at a ninety degree angle
to earth....use low power to check SRW.....adjust match or trim as
required and recheck. Repeat procedure until lowest SWR is obtained and
mount yagi on your mast, pole, tower, etc in a horizontal position
relative to the ground for 2 meter SSB operation. The SWR in the final
operating position may vary slightly but not enough to worry about.
The
measurements on the picture below may be very hard to obtain perfectly,
but don't worry too much about them! Try to get them as close as possible
using whatever construction practices and genius you can find. Round them
off to next highest or lowest number and forget about them.
Perfection is best......... but hard to get in the homebrew
invironment!
The driven element (dipole) shown in the inset is
insulated from the boom which is metal by the homemade non-conducting
bracket which you must fabricate. Heavy Plexiglass works fine as long as
it is thick enough to support the driven elements (one on each
side).
The two halves of the driven element can be attached to the
insulator using muffler type clamps, u bolts, several large wire ties or
what ever your gray matter can come up with as long as the elements can
not move by outside forces and do not touch the boom after final
installation.
The other elements of the antenna should be installed
thru the boom but if this is not possible for you, just mount them at the
required spacing using your genius. The final pattern may be slightly off
center from the boom by a degree or two but us it anyway. The idea is to
have FUN and experiment!
The conductors from the feedline (50 ohm coax)
are attached as you would any dipole. Center to one side, shield to the
other using whatever arrangement of nuts and bolts you may have. Seal all
connections, coax end and antenna elements from mother nature!
If you
decide to use a gamma match instead of this type of mounting arrangement
for the dipole, you won't have to worry about the mounting bracket for the
dipole but then you will have to decide on a way to mount the gamma
match.
You can design your own gamma match for this antenna by using a
separate program that comes with the Quick Yagi antenna design software.
You may still be able to find it on the web.
This project was designed to give
you a starting point in getting on the air on 2 meter SSB fun with a
respectible signal using just a stock radio and it should increase your
effective radiated power near 9 or10 times (plus or minus a few % for
construction errorrrrrrssssss!
EXPERIMENT! EXPERIMENT!
EXPERIMENT!
This editor once built a 6
element yagi for the middle of the band using discarded aluminum sections
for the elements that were "U" shapped from old junk flouresant light
fixtures and attached them to a 1 inch square boom, 16 inches apart for
each and the standard dipole formula 468/freqmhz was used for the driven
element fed with a homebrew gamma match. 5% was added for the reflector
length and each director was shortened 5% shorter each, progressing to the
end of the boom!
SWR was checked as above and was less than 2 to 1 to
start but was lowered a bit, down to about 1.5 to 1 and put up on a 16
foot mast with rotor and it worked
great!
