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Tune Around! Topics For
Technicians! |
DIP-YAG PROJECT FOR 2 METERS  During the December 2002 I worked up the
design for this antenna purely by co-insidence. I needed two stainless
steel selftapping screws and my eye fell on the 3 element yagi that I
constructed for 2m operation. This "odd" measurement yagi with stainless
steel selftapping screws were mounted on a mast 4m high from the ground. I
unscrewed and removed both the reflector and director elements in order to
obtain the said screws. The driven element and funny looking boom were
left intact on the mast. Later that evening I decided to contact Francois
ZS1Q in George. I was greated with the following remark: What did you do know? You are "blasting" me out of the shack. What type of amplifier are you using? I only then realized that I was using this "funny looking" yagi. Tests were conducted and this led to the constructing of the odd measurement "DIP-YAG" antenna. In amateur circles the "DIP-YAG" will rightfully be called a 2 Meter Dipole Antenna. Or will it? Be as it may this antenna give excellent results and is cheap and easy to construct.  Overall layout of Dip-Yag antenna (Use the handy conversion calculators at this link to convert from metric measurements used in this project to whatever you desire!) To construct the antenna we first drill
the hole for the element through the boom. Push the element through
the hole and affix the element with a self tapping screw exactly in the
centre of the element. You will now have a T-shape antenna.
Fit 2 X 10mm Plastic end caps to each opening of the element and 1 X 20mm
plastic end cap to one end of the boom. The SO239 connector is affixed to
a piece of aluminium plate bent in a "L" shape. A hole is drilled at
the short end of the "L" through the plate, the SO239 is fastened with 4 X
8mm bolts and nuts. The long end of the plate is fastened to
the boom with a rivit-gun, approx. 80mm away from the
element.  Photo: Showing the Gamma Match of the Dip-Yag Antenna The gamma match consists of a 150mm
length of 10mm aluminium tubing. The 200mm piece of RG213 co-axial centre
(the outer cover and braid is removed) is slipped inside this tubing which
telescopes into the aluminium tubing. One end is then soldered to the
connector. Sliding the RG213 centre in and out of the tubing tunes the
gamma match. Take the 60mm aluminium tube and drill two 10mm holes 25mm
appart through this piece of tube. Fit the 2 x selftapping screws on the
side of this tube. These screws act as a "lock-nut" to tighten the element
and the gamma match for the best SWR. Affix the boom with a mounting
bracket to the mast. Note: The best SWR is obtained by moving this
matching stub up and down, as well as the sliding of the RG213 centre core
in and out of the 150mm piece of tubing. After obtaining a 1: 1 SWR
tighten all screws and affix the co-ax cable to the boom and mast with
cable ties. One 10mm- and 20mm plastic end cap is affixed to the other end
of the boom and to the end of the gamma match. Seal all holes and openings
with an appropriate water tight sealer. PHASING HARNESS FOR STACKING:  2 X 1.36m 50 ohm RG58 co-ax cable 2 X 386mm 75 ohm Good TV co-ax cable The 50 ohm and 75 ohm cable is joined together for each "dip-yag". The 50 ohm length is affixed to the antenna while the 75 ohm section on the other side is affixed to a "T" piece connector. A identical harness is made for the second antenna. A 50 ohm feed line is connected to the "T" piece and fed to the 2m radio. Note the distance I used between the two antennas is 2 meters. PARTS
NEEDED This antenna is quite broad-banded and performs well during static buildup in the summer months. Thanks to Nico, ZS2N for the use of his MFJ Analizer and for the constructing of the phasing harness during his visit to Mossel Bay in April 2003. I have done extensive tests with this antenna and has subsequently got rid of a Ground Plane Antenna, J-Pole and Slim-Jim. Construct this antenna and you will see why. If you build one of these antennas I'd love to hear from you and see pictures of your work. Finally I would like to thank all Radio Amateurs for their input and help with initial tests. Without this help the project would not have been possible.  Photo: Co-phased Dip-Yag's on the mast. As a result of
several e-mails received I decided to post new photos and more information
including a diagram of the phasing harness.
This antenna gave
very good results. This antenna was used for 2 Meter Simplex
Communications with the one Dip-Yag antenna facing towards Hartenbos and
the other in the direction of the greater Mossel Bay, George and
Sedgefield area. The top antenna facing towards Hartenbos had the
task of getting in behind a hill where one of my good friends stayed at
the time. The J-Pole and Slim Jim used previously could not deliver
the goods. The Dip-Yag did and excellent job in delivering what was
expected from it. A yagi would possibly have done the job, but
then the George radio amateurs could not hear me and I could not hear
them. The stacked Dip-Yag solved the problem and we could continue
with our nightly 2M Simplex Nets.
What about feedline and connector
losses? I used RG58 and a good quality 75 Ohm TV line for the
phasing harness and still received 5.9+10 reports from Hartenbos and
George. Use the best connectors and coax you have. If you use
other cable than RG58 and 75 Ohm TV line then you have to re-calculate the
length of cables as the velocity factor of cable differ. However the
use of RG213, LMR400 and RG58 for the cable going to the radio need not be
re-calculated. Use the handy conversion calculators at this link to convert from metric measurements used in this project to whatever you desire! Although this design use 2 stacked Dip-Yag antennas for additional gain, there is no reason you can not use only one. The METAL mast appears to act as a reflector according to the author of the article SO....you will get a bit of gain from the single "Dip" (dipole)!!! If you decide build one, please give us feedback on how it works for you! 
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