Sunday, March 6, 2011

Antenna Raiser

Here is a really clever arrangement to raise and lower a roof-top antenna to prevent damage to it when underway. Ed Daniels came up with this and provided the write-up and pictures for this article.

Materials

One 6” strap hinge. One piece of 4” x 8” heavy gauge sheet metal bent to a 90* angle. A 3/8” diameter hole is drilled near the top, and in the center, of one side of the angle. This side becomes the top. One ¼” to 3/8” pulley. One length of ¼” nylon line. One block of some sort for the antenna to rest on while stored for travel.

Construction

1) The sheet metal, once bent to a 90* angle, is attached to one side of the strap hinge with exterior grade double stick tape, or an adhesive of your choice. I used the tape. The side with the hole drilled goes up. There is a screw hole at the end of the strap hinge. It needs to be left exposed so you can tie the rope to it.

2) The storage/guide block. This can simply be a piece of 2” x 2” wood with a V shaped grove cut in the top and a 3/8” hole drilled through the bottom that serves as a guide for the line. The item pictured in the photos came from my Stuff Box in the garage. Anything that can hold the antenna in place while it’s stored will work. A piece of sheet metal bent & cut will do.

3) The pulley. I secured it to the roof vent cover with a few pieces of heavy twist tie. If you don’t have a roof vent cover available, you can simply fabricate something to fasten the pulley to from a piece of angle iron, etc. Field tests indicate a simple metal ring can be substituted for the more expensive pulley if desired. Just secure the ring then thread the rope through it.

4) Line up the strap hinge, storage block & pulley so the antenna, when stored, misses the ladder frame. On models with the “luggage” rack, you will need to either rearrange the alignment of the pieces, or attach the storage block to the rail of the luggage rack. Once you’re satisfied with the alignment, outline the parts location with a pencil. Using double stick tape, secure the pieces in place. The side of the strap hinge that is facing the rear of the LD gets secured. The other end where the antenna attaches does not.



5) Tie one end of the ¼” nylon line to the exposed screw hole on the strap hinge. Thread it through the pulley, around the framework of the ladder until its about even with the 5th step from the top, then loop it up, thread it through the hole in the support block, through the 3/8” hole drilled through the top of the sheet metal angle then tie it to the same hole where you started. Using a permanent marker, mark the line that needs to be pulled to raise the antenna. Loosely secure the rope to the side rail of the ladder using electric ties. Field trials showed that metal rings secured to the ladder rails with electric ties serve as good guides for the rope.

That’s it. I found that if I added some weight to the sheet metal angle the unit moved more smoothly.

The photos explain it much better than I do.

The recently completed field test showed that if I forgot to lower the antenna before driving off, the slightest obstruction would lower the antenna to its travel position. In addition, the wind generated while driving also lowers the antenna.

Contributor:

Ed Daniels

Rube Goldberg, Consulting Engineer

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