Adri PA0RDA, a friend of me, is trying to do some DX on 6m for a while now. His antenna position is very poor: he lives in the bottom flat of a 5-floor building. He has a balcony on the rear (south) side, but high buildings are very close, he has no direct sight in any direction. At the balcony he has a Diamond V2000 vertical antenna for 6/2/70, and an MFJ loop antenna for 15-40m. The 6m band is his most popular one, since he get best results on this band. However, since most DX on 6m is horizontally polarized, he needed a horizontal antenna. I remembered an all-direction horizontal antenna made by Jan PA3EGH (one of the members of the local radio club). So I contacted him, and he pointed me at his website. It was the “Squalo” antenna, or square halo. In fact, it’s just a square folded dipole, originally designed by John KG4OSA. It radiates in all directions, with -4dB gain on the sides (compared to the front and back side).
This is a copy of the design, originally published by Jan PA3EGH:
All measurements in the original design are given in inches, so let’s convert them to mm first:
I used 12mm copper pipe for the “loop”, stainless steel strip for the shorting strap and feed point, and a small piece of stainless steel tube for the isolator.
The antenna is very easy to build. The website with the original design provides enough information on how to build it. The pictures suggest some construction details:
I don’t have any equipment for 6m, except a small handy (Kenwood TH-F7) which is capable to receive 6m USB. So after building the antenna, I first attached that radio to the squalo to see if it’s doing something. And yes, it worked! There was an Italian 6m contest, and I heard lots of stations. Next I hooked up the squalo to my MiniVNA to did some tuning. I tuned it (by moving the shortening strip and feed point) to let it resonate on 50.500 MHz, and adjusted the feed point to get 50 ohms on that frequency. The antenna has an operating bandwidth of about 1 MHz, so it covers at least 50 – 51 MHz. That part of the band includes the CW and SSB areas, aswell as the beacons.
I experimented with turning the antenna around while receiving a steady signal (a beacon). There is no “dip” (like dipoles have), but when receiving at one of the sides the signals are somewhat weaker. I didn’t notice any front/back ratio.
On August 15th 2009 I went to Adri to help him with the antennas. He’s blind, so he needs a helping hand now and then. This time we moved his “north” antenna from the living room to the roof. Also, this was a good moment to put the squalo in place, on the south side of his home. I did some final tuning (using my MiniVNA and laptop). Unfortunately the band was closed at that moment. But the day after I received an email that he worked EA5, which is over 1500 km from his site. So the antenna seems to be working.
Chris KC2JB made this great video, showing his way of building the squalo:
PA0RDA’s hamradio shack
Since I built this antenna for Adrian PA0RDA, I added some pictures of his shack here:
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