|2-El.-6-17m-V. Mk Vl||
Dismantable 3-El.-Yagi for the bands 10-17m
This article was published by DK7ZB in " funk 3/2001", S. 41-43
During DXpeditions to OH0, EA9, IS0 and TK I have used some types of lightweight-Yagis. The one with the best compromise will be described here. Picture 1 shows the Yagi 12 m high on a homemade pole. On 12 m I worked a pile-up of JA-stations.
The basis of the construction are constant lengths of the middle, tapered tubes. The outer parts are adjustable for each band. The distances between Reflector-Radiator and Radiator-Director are the same on all bands from 10 to 17 m. When changing the band you only have to adjust the element-lengths.
The construction details are aquired with the PC-program "YA" . On all bands the feedpoint impedance is 50 Ohms. Without the aid of the program this could not been carried out so far. How to use the program I described in .
The gain of real 4,8 dBd seems to be low, but you get some advantages with this compromise. Commercial gains for antennas mostly are to high, please keep that in mind! The bandwidth is high, you can mount this Yagi 6m high and up without detuning effects. If you use the exact dimensions, you will get a well performing antenna.
Table 1: The given details mean that the Yagi is tuned in the middle section of each band at SWR 1,0 (10 m at 28,5 MHz)
Vicarious for all bands I have plotted the important diagrams for the 15m-band, which is very broad. Gain, SWR, Front/Back and Impedance for the full 450 KHz are seen in picture 2. Remarkable is the low SWR. Picture 3 shows the horizontal pattern.
Picture 3: Horizontal pattern in the 15m-Band at 21,2MHz for example, similiar on the other bands
Mechanical details for the boom and the elements
You see the lengths and the diameter of the tubes in picture 4. The middle parts consist of 2 m long 20x1,5 mm aluminium (one part). The radiator has two parts of 1m length. The ends must be slotted and are fixed with clamps (picture 5). All tubes are listed in table 2
The outer parts (12 mm tubes) must be pulled out or pushed in for changing the band. This is done in some minutes. It is easier if you mark the lengths of table 2 with coloured rings for each band.The boom consists of 40x2 mm aluminium, the elements are fixed with automotive clamps (picture 6). For better stability you can mount the middle parts with a short piece of 25x2mm tube.
Picture 4: Lengths of the aluminium-tubes
Table 2: Needed aluminium tubes
|20x1,5mm||2||2,0m||Middle piece Ref, Dir||-|
|20x1,5mm||2||1,0m||Middle piece Radiator||middle part isolated for feeding|
|16x1,5mm||2||1,60m||Intermediate pieces Ref||20cm pushed in 20mm-tube|
|16x1,5mm||4||1,35m||Intermediate pieces Rad, Ref||20cm pushed in 20mm-tube|
|12x1,0mm||2||2,00m||Ends Ref||Lengths table 2|
|12x1,0mm||2||2,10m||Ends Rad||Lengths table 2|
|12x1,0mm||2||1,80m||Ends Dir||Lengths table 2|
Table 3: Lenghts of the outer pieces (12mm-Alu), free ends
For mounting and dismounting you need a 13mm-wrench for all nuts and a screwdriver for the clamps. All parts dismounted are very handy and can be carried on the roof of a car or a motorcaravan.
Together with a 12m-pole I had this yagi with me on some DXpeditions to OH0, TK and IS0 (see picture 1).
Picture 6: Element mounting
for Reflector und Director
Picture 7: Middle part of the radiator
Pictures explain more than many words, therefore we take a look on picture 7. The two middle parts (distance about 20mm) of the radiator are mounted with an isolated tube of hard-PVC or other material. Fixing on the boom is made with aluminium squares and automotive clamps.
A small box with a SO-239 coax-socket contains the toroid balun 1:1 with a trifilar wounding. Up to 300 watts use an Amidon T130-6, at higher power up to 1KW an Amidon T200-6. It is possible to "stack" two cheap toroids for 500 watts with tape.
The schematic of the balun is shown in picture 8. 3x10 wounds of 1,2mm-enamelled copperwire.The three wires must be drilled and wired as shown in picture 9.
Picture 9: The box with balun and coax-socket
Picture 10: Homemade telescopic pole for portable operation
Literature and sources:
 Program YA, ARRL-Antenna-Handbook
 Steyer, M. (DK7ZB): Das Konstruieren von Yagi-Antennen mit dem Programm YA von K6STI, funk 11/99, S.66
 Steyer, M. (DK7ZB): Selbstbau-Yagis für das 10m-Band, funk 1/97, S. 36