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17 METER 3 ELEMENT MONO BAND
CONVERSION PROJECT BY K6TC
all started with an entry into the eHam.net Elmer's Forum.
Tom, K6TC, was looking for help
converting an old friend, the Mosley TA33 Junior, into a single band yagi
for 17 Meters by eliminating the traps. It was just laying around
collecting moss and "Green Slime" (which has collected on the background of this
Now I don't consider myself an antenna
Elmer, but I decided to jump in with both feet and my foot in my mouth
while trying to stay away from the slime. So, armed with
the QuickYagi program, I offered what little assistance I could to a
I had access to WA7RAI'S QuickYagi program on the
harddrive and given the fixed length of a 12 foot boom on the
original TA33 and the design frequency of 18.130mhz, I started to
play with the figures omitting the Green Slime as a parameter.
emailed Tom the measurements and that's how this re-encarnation
The end result, a few emails later and some input by K1WW
and lots of fun had by Tom, is this project based on those figures taken
from the QuickYagi program and a bit of experimentation, ELBOW GREASE and
determination, by Tom!
"Atta Boy Tom"
The Resurrection and
re-birth of an antenna.
years ago a good friend and fellow Ham passed into the SK column of
our W6LI newsletter and while helping his lady sort out his equipment, I
happened upon an old very beat up Mosley TA-33-A junior tri-band
Yagi that he had discarded to his recycle pile, destined for the aluminum
junk pile during the next Boy Scout drive.
Only a 12 foot boom and most
of the aluminum was there, even a couple of the u-bolts and one of
the blocks that mount the elements on the boom. I asked permission to keep
it from the pile and after this nice lady gave her permission along with
free access to go through his junk pile in the garage, I looked to see if
any other parts might be found that would be useful.
little beam home, I got out the good old Brillo pads and a bucket of water
and started to see if I could bring back some of the shine Mosley is so
proud of having on all of their products...not much luck there I'm afraid,
but a start was accomplished until other projects got in the way and
it was set aside.
After meeting my XYL, "Rocky", K6RGC and the
final move to Lakeside, the little beam did make the trip up I-5 and
sat for the next 4 years gathering Oregon's famous "green slime",
buckets full of it!!!...seems that stuff really loves to find motor
homes, antennas, anything made out of aluminum and locks itself on big
time, just like super glue.
I have had an interest in the
WARC bands, 10-12-17-30 meters, for a long time, if for no other
reason, than the contesters haven't really started to congest the bands
with their DX contests every waking moment on the weekends. A decent
QSO can be had just about to any point of the globe should you have the
antenna that can hear the signals that are out there AND be able to answer
their call when they hear you.
My Sommers multi-band beam has been
doing a great job of working the dx for me but I have had a problem
for sometime with the mast I had installed under it when I bought it up
north. Frankly it was a piece of junk and after many many dollars with
Mike at his repair shop, it still wasn't what I wanted to depend on for
The search was on for a new tower!
While the rebuilding of the tower situation was going on, I dug out the
little antenna and got in touch with a Ham pal online, N4UJW
Hamuniverse.com, who hooked me up with a really super antenna
program called "Quikyagi". I couldn't download the program so I told
Don what I had to work with it in parts and he got into the program
running all of the figures so that we could convert this small trapped
triband antenna into a killer 17 meter monoband yagi that would give me
that extra punch to get through those pileups when the conditions were
running on 17.
I used all of the element parts that I already had
and purchased 4' lengths of 5/8 tubing from a flea market in Eugene
to give me the length I needed to eliminate the traps. I was fortunate
enough to be able to recruit AC7IR, Bruce to help out.
We cut the
original elements in half and used them inside of the new tubing and sure
enough there was more than enough length to bring each of the three
elements into exactly where they needed to be and a resurrection took
place right before our eyes!
Now I had a 17 meter yagi
that looks so good I could almost swear it came from the factory built
exactly as it is right now!
I thank Bruce,
AC7IR and Don, N4UJW for their help, without which it would not of
happened at all. Tom.
"Quickyagi" by WA7RAI, arrived at these lengths for the elements based on
.625 inch diameter elements from end to end and NOT TAPERED. The center
design frequency was 18.130 mhz. Antenna is driven as a dipole (direct
connection to driven element) thru an "Ugly
Balun" 1 to 1 ratio placed close to boom..
The figures below
are total length for each element. This is what the program
Reflector length 27.41 feet
Reflector space to driven
Driven element 26.35 feet (remember this is a dipole type
element open in the center)
Director space 7.39
Director length 24.79 feet
You can round the numbers to
the next higher digit and not make much difference and make construction
much easier....can you read .79 inches on a tape measure?......not me .80
would be easier....hi!
These numbers should yield (in free space)
about 7.5dbi gain and 23.8 f/b according to "QuickYagi".
Of course this
is the ideal situation.....bet you don't have that! HI!
the program several times with different values for element sizes,
lengths, optimizing, etc.....it appears that there is not enough
difference in each to make any difference on the receive end.
this is because of the restriction to the 12 foot boom length which we had
to work with.
Click here for ASSORTED
PICTURES TAKEN DURING CONSTRUCTION
MODIFICATION OF THE TA33 JR
FOR TRIBAND 10-15-17
Comments added for
the project courtesy of
On the TA33 everything between the boom and the trap is
for 10 and 15 meters. Everything from the outside of the trap to the end
of the element is for 20 meters.
Lean the antenna pointing up
against a non metallic support with the reflector on the ground.
Connect your antenna analyzer or SWR bridge.
Adjust the driven
element length outside of the trap equally on both sides of the element
until it is resonant on 17 meters.
Once it is resonant on the
17-meter band measure the overall length of the driven
Reduce that length by 5% this will be the new length for
Add 5 % to the driven element length. This is
the new reflector length.
Now you have a tribander for 10-15 and 17
All the length changes are outside of the traps.
change any length between the trap and boom.
Here is a way to
get in the ball park on the length of the driven element for 17
Make sure the driven element is resonant on 20
Measure the overall length of the driven element, lets say it
is 28 feet.
Now calculate 468/14.200 = 32.9 ft...Now 468/18.100 = 25.8
Subtract 25.8 from 32.9 = 7.1 ft..Divide 7.1 by 2 = 3 1/2 ft.
Reduce the driven element on each side, outside of the trap, by 3 1/2
ft and that should get you in the ballpark.
Good Luck, Ray, K1WW
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