Portability Is GOOD
Portability is a good quality, especially in an emergency situation. Being prepared, trained, and available to assist in such times is a lofty goal that many in the Society strive for.

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One of the first to become a "building project" within the Society, was the PAC-12 vertical antenna. For those who do not know about this little antenna, here's a few links:

Several intrepid Society members undertook the challenge of building these gems. One produced by Roland (KC5UNL) was actually documented over at his blog, but here are a few pictures, just to show what kind of thing we are talking about:

This is KC5UNL's version of the PAC-12 setup in his front yard. As is the case with all of these pictures, if you wish to see a larger version, just click on the picture.

As part of the function of a PAC-12, there is a common theme that it can be assembled in several ways. As such, KC5UNL proposed the following scheme. The heart of any one configuration of this antenna is the coil. To change band, you had to swap out coils and "diddle" with the resulting antenna. Rather than have the limitation of having to have an antenna analyzer in the field with the PAC-12, KC5UNL came up with the following way of documenting a given configuration:

1.2SWR @ 14.060MHz
G-1-F-2-C-0-W-57-T

What this general block of information gives us is defined as follows:

  • The first row denotes the SWR of the system at a given frequency.
  • The second row is broken up into letters and numbers by the "-" symbol as follows:
    • "G" defines the type of base. "G" for the base shown. "S" for a spike base is another option
    • "1" defines that one of the twelve inch aluminum rods is between the base and the next element. This could be "0", "1", or "2."
    • "F" defines the feed point.
    • "2" defines that one of the twelve inch aluminum rods is between the feedpoint and the next element. This could be "0", "1", or "2."
    • "C" defines the coil.
    • "0" defines that one of the twelve inch aluminum rods is between the coil and the next element. This could be "0", "1", or "2."
    • "W" defines the whip.
    • "57" defines the number of inches of "whip" that is extended.
    • "T" defines the tip of the whip.

The proposed standard for the group was to make this sort of label a "standard" and to affix it to each and every coil produced so that we could all mix and match parts and pieces on group interaction days like the "ARRL Field Day."

This picture covers the details of the center feed point. This is not the original design presented in the instructions but a derivative. Note it has connectors for both PL-259 and BNC cables. KC5UNL thought this best so that operations would never have to cease for lack of an adapter, regardless of which feedline was brought to the field on a given day.

As may also bee seen, KC5UNL used four ground radials. What might not be so evident is that they are four separate strands of "computer ribbon cable," fifteen (15) feet in length. Each strand was separately stripped of insulation and as a "gang" of four wires, were crimped into a ring lug.

In this picture, we can see the coil and the guying system originally used. The coil is wound on a piece of 1/2 inch PVC water pipe, and is 23-turns of 22-gauge wire. This picture, taken somewhat early on in the process, shows the coil being held in place by some low-tack painter's masking tape.

The guy lines are attached to the structure by a 1/2 inch PVC cap "upside-down," mounted between the coil and the whip. Then, around the cap, there are four holes through which small diameter nylon rope is strung off to tent stakes

After looking at the system, tripping over the guy lines and just about breaking the entire PAC-12 antenna in two, KC5UNL decided it would be good to redesign the system with a bit of "give" in it. So, looking around his shop, these bungies were the end result. What little metal is involved in the hooks on the end don't seem to affect the SWR of the antenna much, as he didn't hook them directly to the 1/2 inch PVC cap, but rather a short distance away via some cable ties.

This additionally allows for "fixed length" guy ropes to be pre-made as part of the PAC-12 kit. The bungies also allow for uneven ground.

After trying to clean it up a bit, adding some "brighter" colored guy lines, some safety flags, etc., KC5UNL got down to actually testing it. At the end of the morning of testing, the following points seem to rule the day:

  • Having the ground radials go straight down along the side of the vertical rod was best (lowered the SWR about 0.1).
  • Having the feed line come into the feed point connector at as close to 90 degrees to the vertical mast was best (again lowered the SWR about 0.1).
  • There was more to learn, with each new coil wound.
  • The final coil was
     
    1.2SWR @ 14.060MHz
    G-2-F-2-C-0-W-57-T


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Others on the Web
There are several portable antennas that are used within the Society. Several that exist in the Society are:
  • The Buddipole, a multi-band, configurable dipole antenna.
  • G5RV
  • General dipoles