Monday, 29 July 2013

Project 11: Better quality 150MHz Dipole

                       This is essentially an upgrade of project 7 Airband Dipole . I thought the results from that roughly built, simple,"thrown together" Dipole were encouraging enough to build something more permanent. Once again, the materials were cheap : a 3 way junction box, 1 metre length of aluminium tubing, 8 cm of old nylex garden hose and silicon sealant.
Hose sections used as packing
                       The tubing came as  1 m length so i cut that in half. The tubing does not fit snugly into the "T-piece" so some packing is required. In this case, 2 bits of old garden hose cut into 4 cm sections and then cut down the middle, opened up and pushed onto the tubing which then fits nicely into the box. The bits of excess hose are then trimmed off.

Packing trimmed and holed drilled
                       After that, the holes are drilled for the coax fittings. The standard nuts, bolts, washers and auto-electric crimped type connectors are used. The box cover plate is screwed back on, and silicon sealant is applied just about everywhere.
co-ax fitted

cover replaced
                       Once that had cured, it was mounted in place of my weather station which despite being guaranteed to be made of U.V. resistant plastic, is falling to pieces after 5 years in the aussie sun. This time the antenna is mounted a wave length away from the mast which i noticed is the practice used on commercial VHF antennas.
                       Unsurprisingly, this gem of an antenna performs far better than its predecessor. I have really enjoyed the progress of these 2 builds. It started as in idea i saw on the web, then to a rough prototype for proof of concept and now the final build. A very simple, top performing antenna build, enjoyable from start to finish.



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