Wednesday, 29 July 2015

Tape Measure Satellite Beam - VHF Build

A couple of hours today, and I have the VHF section of the tape measure beam built. The hardest part is getting the holes marked and drilled accurately. There are three 3/4 inch holes to be drilled on each side, and these have to line up with each other on each side, and with each other on either side! This was done by first drilling a pilot hole all the way through, and then expanding it out with a tapered reamer bit.
The boom is 1 inch diameter, the holes are then plugged with 1inch long sections of 3/4 inch tube. These are cut using a pipe cutter, which leaves nice tidy edges.

With the tape element in place, the plug is pushed tightly home. By reaming the hole more on a particular side, the hole can be adjusted to get the elements in best alignment. Once complete, these will be made permanent using a PVC welding solvent glue.

 The picture above shows the director and reflector element installed, and the driven element 'mocked'up' using Jubilee clips. You can see that some alignment work is necessary, although it would probably work just as well without.

The next task was to attache the driven element sections. A circular wire brush and mandrel in the pillar drill made light work of removing the paint from the ends, and then three M3 fitting holes were drilled.

The 'plug' section here is 3 inches long. Carefully marked and drilled to correspond with the element that will be attached. The reverse side has 6.5mm holes that allow screwdriver access to the bolts. Each element is fitted with a pair of 'contact' bolts, with M3 solder tags on each. A third bolt secures the element near the end of the plug.

The antenna with all elements installed is shown below. At this stage some adjustment of the element lengths on either side was needed for the director and reflector, this being done by measuring both sides and pushing out the plug, adjusting the tape, and pushing the plug back in, until all was equal.

 In this final picture, both sides of the driven element are attached.

Since taking these pictures, ive attached the coax feed to the driven element, wound the 6 turn balun onto the shaft, and added the BNC connector. I have yet to put the antenna onto the antenna analyser and check the match, which is why I havent yet installed the hairpin matching section. I should get this done in the next few days. All being well, the VHF side will be complete soon, and I can work on the UHF section.

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