Experimental setup square halo (3)

 

  PA9X Jean Paul wrote me an e-mail this morning. Asking if I already continued with the halo experiment. I didn't because of too much other things going on. But I finally had some time today.

And as you can see it was just beautiful weather, exactly what I need to do some antenna experimenting. 

The goal for today was adding the 12m band element. Actually it went well. Learning from the previous element cutting I made a 6m long double wire. I was afraid I would get an open ended loop wire again like the 17m band but was surprised to see a good resonance and SWR already at first sight with a closed loop "dipole".

This is the result so far:

I'm not disappointed at all. Except the 17m band, SWR is as expected. I wrote down the frequencies and peak SWR at one meter height and then raised the antenna to two meter height. I saw the SWR peak shifted up a bit, about 20-50KHz depending on band. Something to count on when tuning this antenna. The analyzer photos were taken with the antenna at two meter height.

The 17m dipole is not closed but has open ends. Previous experiments showed no resonance when closing the ends. It is not clear to me why 17m is behaving like that. The other "dipoles" are in fact all closed full wave loops. To see if SWR/resonance would change I messed around with the feedpoint. I bundled all the "loop" wires to see if this had any effect, it didn't. I tried to hang the balun in several different ways, it did only have a negative effect. In the end I cut back the long "tweaking" open ends of the 17m dipole and made the wire a bit longer. I managed to get the SWR down to 1,6 and X=6. Actually resonance is now around 17,9 MHz. It is not that bad and I'm satisfied for now. 

I decided to make everything watertight and park the antenna at the side of the garage. When removing the 6m/4m duoband beam for winter I will probabely mount the square halo on top of the tower. If time allows and I feel the time is right I probabely mount it earlier...haven't decide on it yet.

If you like to experiment yourself here is some tips:

Don't shorten the wires like you do with dipoles. Half wave is half wave. 300/f = meters dividing in half is the length to start with. You can always cut if needed.

Distances are probabely important because the wires will interact. It is to you to experiment. Starting points: Mounted balun on boom at 100cm from center. Mounted wires on spreaders 12m wire at 105cm, 15m at 126cm, 17m wire at 146cm and 20m wire at 191cm from center. I use shockcord to  connect the ends together.

Remember this is an experimental antenna. If it doesn't work as expected don't blame me ;-)