Tuesday, July 24, 2012

Building a K2AV FCP 160-M Antenna

Tim, K8RRT, after his wind damage and while waiting on his insurance adjuster, decided to improve his 160-M antenna by adding K2AV's FCP (Folded Counterpoise) to his Inverted-L.  The tips and tricks used here were mostly gleaned from others who had previously built this antenna.  The first two images below (with blue borders) are from the description of K2AV's FCP antenna on WØUCE's web site HERE.  You can find more info on the antenna including the information on the FCP transformer on that web site.  Click on any image below to see it larger.


Below is a diagram of the spacers Tim used on his FCP.  The brackets ( [ ] ) indicate where the No. 12 wire is bent back and begins another run.  The asterisk ( * ) indicates where the wire ends.  The 3-wire half is shown at the top.  Each half is 33-feet long.  The wire is one continuous run.  "FCP" indicates where the wire is connected to the FCP transformer.  Place the two diagrams below end to end with the "Mid" section of each overlapping as the center to see the full FCP arrangement.

FCP Transformer

[|----|----|----|----|----|----|----|----|----|FCP  
[|----|----|----|----|----|----|----|----|----|
*|----|----|----|----|----|----|----|----|----|

End   1    2    3    4    5    6    7    8   Mid


--|
--|----|----|----|----|----|----|----|----|----|]
--|----|----|----|----|----|----|----|----|----|]

 Mid   1    2    3    4    5    6    7    8   End


One spacer at each end and 8 more spacers in the center make 9 sections between spacers.  For 33-feet that means each spacer should be 3-feet 8-inches (44 inches) from the next.

Spacing the wire 4-inches apart means you need spacers a minimum of 9 inches long on the side with 3 wires and 5 inches long on the 2-wire side.  You should probably make them 10 inches long on the 3-wire side and 6-inches long on the 2-wire side to leave room for putting caps on the ends.  K2AV recommends putting caps on both ends and drilling a small weep hole in the bottom cap.

FCP Spacer Attachment
End spacers should probably be a bit longer for attachment purposes.  We cut the spacers from ½” Schedule 40 PVC.

Here is what we made:

     2 - 12” spacers (End of 3-wire and Center spacers)
     8 - 10” spacers (3-wire spacers)
     8 - 6” spacers (2-wire spacers)
     1 - 8” spacer (End of 2-wire)

3/32” holes were drilled in the spacers for the No. 12 bare wire.  The holes were drilled at slightly different angles to provide some extra tension on the wire.

We cut the No. 12 hard-drawn bare copper to 168-feet.  That is based on 5 lengths of 33-feet each for the counterpoise plus 1 foot for the end interconnect space and 2-feet for connecting to the FCP transformer.

All the spacers were strung on the wire first.  This end will be the unconnected end of the FCP ( * ) and the No. 12 wire was wrapped back on itself at that point.   We then measured 66-feet and that became the end of the 2-wire section.  The No. 12 was bent and re-inserted in the second hole of the 2-wire End spacer.  That wire was then threaded back through all the other spacers 2 at a time.  One of us held one spacer and kept the wire flowing freely while the other pulled the wire through the second spacer. We did this about 10 times but each time the amount of wire being pulled through got less so the process went faster each time.

When we reached the beginning spacer, the No. 12 was bent again and re-inserted in the third hole of the End spacer of the 3-wire section.  The wire was then threaded back through the remaining 3-wire spacers to the Mid spacer.  Measurements were made again and the wire was bent where it came through the Mid spacer leaving 2-feet for attachment to the FCP.

The spacers were then fixed in place by placing a black nylon zip tie (Ty-Rap) diagonally across the spacer.  Before doing that, measurements were again checked to make sure the spacers were evenly spaced at 44 inches.

Tim's installation was similar to the Pole Mounted FCP in the image above.  His center support was a 4x4 post.  His end supports were military surplus fiberglass poles which were placed over a short metal fence post driven in the ground.  The poles were then back-guyed to provide the necessary tension on the FCP.  In the photo below Tim has put one thin PVC in the center of one half of the FCP to give further support.  He will put another white PVC on the other half later.
The full FCP Counterpoise with Fiberglass ends and one PVC center support.

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