2m-Yagis with the 28-Ohm-DK7ZB-Match
(Matching for the 50-Ohm-Yagis see down!)
Short means, that these Yagis have not the length for EME-groups... All Yagis have a stretched dipole (the lengths in the tables are from tip-to tip), for the details see
Several contest-crews are meanwhile operating with DK7ZB-Yagis stacked vertically.
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All *.YAG-Files with various element- diameters for short DK7ZB-Yagis (5KB) for YA or YO from K6STI (4, 6, 8, 10mm) 4, 5, 6, 7 and 8-El.-2m-Yagis (short_2m.ZIP) |
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The elements are mounted insulated with Polyamid-clamps (Konni), the screw in the electrical "zero-point" has no influence to the length of the element and is connected to the boom. "Insulated" means, that no part of the element is "short-cut" by the metal of the boom. Boom 15x15mm for the 4-, 5- and 6-Ele.-Yagi Boom 20x20mm for the 7- and 8-Ele.-Yagi |
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Another method with homemade clamps (cheap and easy) by Adam, 9A4QV. See further Details on his home page: |
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Clamps for 20x20mm-Boom made by Jan, SP9MQB 10 Pieces for 2.-Euro + shipping
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If you use not-insulated mounting through the boom, you need a correction factor. The element must be longer, because a part of it is electrically shortened. The boom correction for some diameters is as follows:
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Boom |
10mm |
15mm |
20mm |
25mm |
30mm |
Element
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+1,2mm |
+2,6mm |
+4,4mm |
+6,8mm |
+9,5mm |
The boom correction uses the DL6WU-formula:
C = (12.5975-114.5 * B) * B * B
C=Correction factor for one element half (for full element x2) in wavelengths
B=Boom diameter in wavelengths
For very long Yagis with small bandwidth it is better to mount the elements insulated, because the factor must be seen in relationship to the reactance of the elements, that means another factor for the shorter directors. With a constant factor you can change the performance of your Yagi to worse conditions.
The box with the 2xlambda/4-75Ohm-coax and the socket, three different antennas
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The Box of the 4-El.- Yagi with 1m Boom and 10mm radiator |
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Better mechanical stability with the construction of Udo, DK1FUN |
| With CATV-cable (full
PE) of 34,5cm length you can mount the cable as a choke in a small box
for a better waterproof construction.
This is the 4-El.-28Ohm with 0,76m boom and 6mm radiator. |
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2m-Yagis with the 50-Ohm-DK7ZB-Choke
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The Yagis with an impedance of 50Ohm reach not the highest gain and the best patterns, but they are very uncritical for constructing and have an extreme broadband design. I use stretched dipoles with an isolated middle part and a coaxial lambda/4-choke. The choke is wound with 34,5cm RG-174 (for 100Wtts) or 37,0cm RG-188-Teflon (for 200Wtts) on a piece of PVC-tube. One end of the choke is connected to the radiator, the other side is connected to a coax-socket witch must be grounded to the boom. There are no currents on the shield of the cable and you get a very good SWR of 1,0! The Yagis work without any corrections, if you use the given datas. You can use this construction instead a 200/50-Ohm folded dipole (easier to tune!) in other descriptions.
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