KU4AB antenna review
E Olson
I have been meaning to write a review of the KU4AB halo antennas for a long time. I just put it on the back burner and it dried out. So… finally here goes! I have used KB6KQ halos for some time now and I am pleased with the results I have had on 6 and 2 meters with single loops. The KB6KQ 432 MHz one I have never seemed to get far but should be expected. I have always wanted to try a phased pair on 2M and 432Mhz but with the passing of Norm the opportunity never came. I found KU4AB advertising in QST and looked them up on the web. The prices were reasonable and they looked OK so I ordered complete kits with antennas and phasing harness for both 2M and 432 MHz.
They shortly arrived and my first impression when seeing them in person was they may not last long when bouncing and vibrating on a vehicle for a long time. However I was proven wrong after using them on my truck in the September 2008 VHF contest as a rover and then again over the mountains to the conference in Moses Lake- they held up marvelously! My second thought after taking them out of the box and deciding how to mount them was just that: how am I going to mount these things with the supplied U bolts. You see they offer 2 mounting sizes: 1.5 inches and 3/8 inches. A 3/8 inch mast did not seem strong enough so I ordered the 1.5 inch ones. However due to constraints from the rack on my truck at the time and mounting hardware sizes available I could not use 1.5 inch tubing; 3/4 inch EMT was the biggest I could go. So I designed my own mounting brackets out of aluminum channel and stainless bolts. After spending most of a day with my drill and Dremel tool I had mounts that actually worked really good. The coax connectors on the harness could be better types- they use compression for the shield connection but work.
When assembling the antennas on the mast and following the supplied instructions I came on a puzzling question: the 432 antennas were to be mounted with the coax connectors both facing down but 2 meters required the connectors to face each other. This resulted in the center conductor feed points to be on opposite sides for 432 MHz but on the same side for 2 meters. With my limited knowledge of phasing I thought the 432 instructions were wrong as the feed needed to be on the same side. I emailed Phil about this and he said 432 was actually correct but he included the wrong instructions for 2 meters; the 2 meter coax connectors also needed to face down on both antennas! I emailed back explaining the center conductor directions just to clarify what I was seeing but before I could get a reply I found the answer in the ARRL Antenna Book: it lies in the phasing harnesses. They have ¼ wave of 75 ohm coax on one side and ¾ wave on the other. So unlike most phasing situations where the feed point is on the same side and equal lengths of coax are used this uneven scheme requires the feeds to be on opposite sides so you get a doughnut pattern at the horizon instead of an end fire system shooting straight up (which Phil alluded has been used for satellite work). Sneaky and cool!!
The on the air results were good during the Sept 2008 VHF contest running as a rover. The big difference seemed to be 432MHz!! With my old KB6KQ 432 halo I could barely get out of whatever grid I was located in. I worked 2 grids away from all of my stops on both 432 and 2M with these new phased loops!! I forgot to take my old 432 halo for RX comparisons so no “data” there. I did not think of trying a single KU4AB comparison to the phased pair. I am pleased with the results of these phased antennas. But before you all get visions of grandeur halos are no substitute for a beam. However for doing a rover entry like I did they are not bad.
I hope this helps someone! I included 3 photos of them mounted on my old truck.
73 de Eric N7EPD
Bruce Junkin
Mark Van Winkle
Eric, your timing could not been any better. I am sitting at my desk with 2 m2 loops trying to decide how I would mount them. Your photos were of interest to me. I only have one for 2 meters and 1 for 70cm. I think I will mount them to a rack I have on top of my fiberglass canopy. Not sure how far to space them, probably about 16”.
I thought It would be fun to try them traveling for work and between rover locations.
Thanks for your review and photos,
Mark
K7HPT
DN17
From: PNWVHFS@googlegroups.com [mailto:PNWVHFS@googlegroups.com] On Behalf Of E Olson
Sent: Sunday, February 01, 2009
10:15 PM
To: PNWVHFS@googlegroups.com
Subject: [PNWVHFS]
KU4AB antenna review
I have been meaning to write a review of the KU4AB halo antennas for a long time. I just put it on the back burner and it dried out. So… finally here goes! I have used KB6KQ halos for some time now and I am pleased with the results I have had on 6 and 2 meters with single loops. The KB6KQ 432 MHz one I have never seemed to get far but should be expected. I have always wanted to try a phased pair on 2M and 432Mhz but with the passing of Norm the opportunity never came. I found KU4AB advertising in QST and looked them up on the web. The prices were reasonable and they looked OK so I ordered complete kits with antennas and phasing harness for both 2M and 432 MHz.
Marshall Williams
The reason that the 432 antennas must be mounted with both coax connectors down(or up) is that the phasing lines for 432 are the same length on each side. On 2M, in order to reach the top antenna, he has added an extra 1/2" wave length of coax(as you have said). That extra 1/2 wave of coax maintains the impedance, but it INVERTS the phase. By putting one coax connector up and one down, you invert the phase again, which makes the antennas back into the proper phase.
I have several rovers out that have these antennas. They do work well and allow the rovers to drive along and make contacts rather than just going to a spot, making whatever contacts they can make, and then moving on to another spot. Sometimes, that saves the rover guys a lot of time...sometimes not. It depends on the propagation conditions.........which by the way were absolutely terrible down here this Jan.
73 to everyone....Marshall K5QE
E Olson wrote: