Portable lightweight 5-element 2m DIY Antenna (SOTA)
This is a short description of one of the antennas I use for less serious hikes and for SOTA activations where the access is easy and short. Its not as small as my 4-element yagi but has even better performance of course.
The antenna is based on a design by DK7ZB and former NUXCOM.
It is build from basic materials:
- Aluminium welding rods with diameter 4 and 3.2 mm from Ebay
- Insulation pipes 25mm diameter (16mm for the loading coil)
- PVC clamps
- 50 Ohm coaxial cable (eg. RG174 or RG188)
- Insulation tape
- Luster terminals to extend the aluminium welding rods**
** Usually the rods sold on Ebay are too short for the longest element, so you have to attach another short piece with the luster terminal.
For FM use the polarisation is vertical. I mount the antenna on hiking poles. In order for the antenna to be (more or less) free from interfering with the hiking poles I built an extension with 25mm insulation pipe.
Construction details
For the radiation elements I did drill a hole of 3 mm into the PVC clamps, that way the 3.2 mm rods are quite hard to push into to holes but once there they do not need additional fixation.
Radiation elements of the 5 element yagi antennaRadiation elements of the 5 element yagi antenna
To attach the radiator element (4mm) I used a piece of wood. The radiator rods are attached to the piece of wood by small holes I drilled into it. To fix the rods in the wood I used small metal screws, those are at the same time the connection terminals. The loading coil is attached to the piece of wood as well. The antenna design is 50 ohm, the loading coil is used to act as a sheath current filter. The whole plate is again attached to the pipe with a PVC clamps.
Radiation element and loading coil of the diy 5-ele lightweight portable yagiRadiation element and loading coil of the diy 5-ele lightweight portable yagi
Radiation element and loading coil of the diy 5-ele lightweight portable yagiRadiation element and loading coil of the diy 5-ele lightweight portable yagi
Radiation element and loading coil of the diy 5-ele lightweight portable yagiRadiation element and loading coil of the diy 5-ele lightweight portable yagi
As you can also see above the coaxial feed line is directly attached to the loading coil. This has four advantages compared to using a connector: it's lighter, the setup is faster, you cannot forget the cable ;-) and the feedline can run inside the boom, keeping it away from the radiation elements and helping therefore a good SWR.
For the mast as mentioned I use the hiking poles which I attach to each other an to the extension pole with velcro tapes. The antenna itself including cable (I used 6 meters of RG58) weighs around 450 g.
Lightweight portable diy 5-ele Yagi for Sota.Lightweight portable diy 5-ele Yagi for Sota.
Lightweight portable diy 5-ele Yagi for Sota.Lightweight portable diy 5-ele Yagi for Sota.
The boom itself is also cut into 2 pieces and the whole antenna fits into a plastic document roll from Ebay. It is attached to the extension boom by another piece of wood to which I attached appropriate plastic clamps:
Connection plate between boom and mast of my 5-ele lightweight portable yagi antenna.Connection plate between boom and mast of my 5-ele lightweight portable yagi antenna.
As mentioned above for transportation I can put the whole arrangement into a document pipe. The whole package weighs around 1.1 kg then. The performance is very good, see antenna analysis below.
When building our own antenna my advice is to make sure the measures given related to distances and element length are followed precisely. You can cut the radiation element 1cm longer as given to give some room for SWR adjustment but take into account that you cannot change the optimum SWR far from the center frequency for which the antenna is designed by just changing the length of the radiation element. The whole arrangement of distances and length of all 5 element is relevant and is what makes the design a complex calculation.
