Stacking 2 Meter Halo Antennas by Mike Fedler N6TWW

January 14th, 2007

Project Background & Goals
This is step two of the process to build and install a pair of halo antennas for use on 2 meters SSB. The first goal in the project was to build a 2 meter halo antenna that was more robust than my previous design. The experimentation needed to build the first loop of my new design really paid off. The second antenna which was built to match the first antenna had nearly a one to one match before any adjustments were made. In order to get a flat 1 to 1 SWR very little adjustment was needed. The main goal for this project was to get the two loop antennas mounted on the same mast and ready for the phasing hardness build. This project is really very simple with just mechanical work to be done.

Preparation for attachment of second loop. (Click for larger view) There wasn't too much preparation needed for this project. Just gathering the parts to be assembled along with a few tools and something to hold the antennas off the ground while I worked on them. In this picture you can see that I have the first antenna that has already been installed on the fiberglass mast as will as the second antenna which is not yet installed. Please note that each antenna has a separate coax feed line attached to it. That is not really needed at this stage but I had already attached a feed line to each antenna for SWR adjustment. Once both antennas are mounted a phasing harness will be built to connect the antennas to a single feed line.

Marking the location on the mast for the second antenna. (Click for larger view) In this picture you can see me marking the location where the clamp for the second antenna boom will be installed. The distance I chose for the antenna separation was 48". I measured from the clamp on the top antenna down the mast 48" and marked it with a marker pen. You can see the spacer shim that will be used between the U-bolt and the mast sitting on the red seat of the mechanics cart. It is the small semi-circular piece of white PVC. This was made previously for use at this time.

Second Loop Installation
Installing the second loop antenna on the mast. (Click for larger view) Now that the location for the second loop has been marked, the installation can begin. All that was needed was to put the U-bolt and shim around the mast then to insert the U-bolt through the boom. That is what is being shown in this picture. After the components are in place, tighten down the nuts on the U-bolt. Note that both antennas need to be positioned with the same orientation. That means that both booms needs to be parallel to each other rotationally. If you were to look down from the top of the mast, both booms should line up exactly. Also the side of the antenna that was chosen for the top of the first antenna should be chosen as the top on the second antenna. This is important so that both antennas radiate with the same pattern. This is another good reason why both antennas should be built exactly the same. They should be twins. Once everything is lined up, tighten down the U-bolt nuts and the installation of the second antenna is complete.

Assembled & Ready For Harness
Loop attachment to mast is now completed. (Click for larger view) At this point you should be completed with the installation of the second loop on the mast. This picture shows the completed assembly prior to building the phasing harness. Note that the loops are both orientated in the same direction as described in the previous paragraph. Also note that there are still two coax feed lines, one from each antenna. These will be cut to length and combined once the phasing harness is built and installed. I ran into a problem when installing the second antenna. The loop did not want to sit exactly perpendicular to the mast. The way I solved this was to attach a hose clamp to the mast and stretch a wire from that clamp to the ends of the U-bolt. That allowed me to apply enough tension to secure the antenna in perpendicular alignment. If my construction process had been better when I first built the boom, I could have avoided this situation. You can also see in this picture how I have secured the toroid cores to the mast using electrical tape. Now the only thing left is to build the phasing harness.

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Michael Fedler, 2007