This is a simple vertical groundplane antenna intended for mounting atop a 10m Squid Pole. These can be made to nearly any frequency you desire, and can be self-supporting if needed. The main limitation is the stiffness of the wire used.
The antenna gets its name as the original was one I quickly knocked up just prior to a horse endurence ride event that took place at Donnybrook in 2011. I was assisting Brisbane Area WICEN with the emergency communications at this event, and this antenna, worked very well. 10W was more than sufficient to get back to base on 2m FM.
The design is very simple. You’ll need some stiff copper wire, and a panel-mount BNC connector. I used some strands from a thick mains cable: this was being tossed out at a ham radio meeting some years back. The cable had a black plastic coating and inside were 7 strands of solid copper, each about 2mm thick. Perfect for small antennas.
Similar wire can be found in non-stranded house mains cable.
First step is to work out what length to cut the elements. They should all be roughly the same length. This can be calculated by the simple formula:
which if you take as being the velocity of light in a vacuum (~ m/s; radio will travel a little slower through air, but who’s counting?) and as being and solve for you get 2.04m as the wavelength. We want ¼ of this, so I’ve aimed for 51cm long elements.
Don’t worry about them being perfectly straight when measuring, extra length is good at this point, you’ll want a good 2cm extra. You can make a wire shorter, you can’t make it longer.
Measure and cut the 4 elements. 3 will become your groundplane, and the 4th the radiating element. Also cut off about 10cm or so, give or take, which will be the ground wire used to hook the groundplane elements to the BNC connector. Also add to your parts list, some small velcro strips: you’ll find these handy to strap the coax to the squid pole.
Start with the short piece of wire. You’ll want to bend it into a rough triangle shape, with loops of wire at the corners. The groundplane radials will loop through these holes. The excess wire should be coiled up to one side: this is the loop the squid pole will pass through. The BNC connector will be fitted in between the 3 small loops.
Be sure you can still put the nut back on.
Take 3 of the four elements, and make a hook at one end. Pass this hook through each of the small loops in the triangle. Try to make them sit roughly straight out from the centre of the triangle, then solder each hook into the loop.
Having done this, put the BNC connector in and do the nut up tight. You can do away with the eyelet with the solder tag. To finish off, take your remaining element, make a hook just big enough to go around the centre pin of the BNC connector, then solder into place.
To finish off, bend this until it is vertical. The antenna is now ready for tuning.
Double check the length is about right. It should be around the 51~52cm mark.
To check the tuning, use a SWR meter or antenna analyser if you have one. Here, I used the built-in SWR meter on my Yaesu FT-857D. When using a SWR meter, ensure you’re running minimum power. The following are some results from my set. It is at this point, you do any trimming of your antenna. The following are without trimming the antenna, you’ll note that in most examples, the SWR is very low, just a point or so showing up on the left side of the screen.
To mount the antenna on your squid pole, feed the tip of the squid pole through the remaining loop. Bend the tip of the antenna around the tip of the squid pole. Hook your coaxial cable to the BNC connector and use velcro straps at regular points to hold the coax to the side of the squid pole.
Recommended coax for this purpose is RG-195. RG-58 will work, but is lossy, RG-213 and LMR400 are too heavy to use on a squid pole and will cause it to bend or collapse.
Update: This antenna performed quite well. Saturday, we used it for 2m packet, providing a digipeater for the stations in our area in case they couldn’t reach the main node (at “the pineapple farm” just outside Imbil). We had stable packet communications all day. Since the stations around us found they could work the main node directly, we swapped antennas around and used it instead for a VHF/UHF cross-band voice repeater. Signal reports were good through the Imbil state forest.