I first made a Buddipole portable antenna many years ago. I used heavy duty plastic pipe which was threaded so that all the sections would screw together. It worked very well. My return to /P operation required a relatively lightweight and easy to assemble antenna for 40m – 10m but this time it will be for use next to the car and not backpack portable. The usual 5m painter’s pole would be used to support the antenna.
I thought of using the heavy duty plastic pipe again but getting a quote for nearly £70 for pipe and fittings got me looking at other, cheaper ways to do the same thing.
There is a design for a long version of a Buddipole derived antenna by AE5JU which uses ~5ft lengths of half inch fibreglass rod used for electric fence supports in the US. Unfortunately there is no UK equivalent. Fibreglass rod is available at around £30 for a 4 metre length (plus delivery) but I found some standard tent poles which are 30 inches long and of the right diameter; a pair cost just £7.20.
There is no UK source for 72 inch long whips but they are available on the official Buddipole web site at just $6 each but shipping is expensive. I chose the longer whips 9.5 ft at $18 each as this would make a dipole that needed no loading coils for 10m, 12m, 15m and 17m.
Only two problems remained: how to fix the whips to the rods and what sort of tee piece to make. The whips come with a 3/8 24 threaded bush. AE5JU has a neat solution which involves soldering together parts that I just could not find in the UK. In the end I made two ferrules from 3/4 inch brass rod. Lacking access to a lathe meant that they had to be made using hand tools and a small pillar drilling machine. (Click on any image to enlarge.)
Ebay was a good source for the brass rod, the 3/8 24 taps needed for the thread and the tapping drill. The rest was relatively easy and the first ferrule was made in an hour or so.
The completed ferrule was glued to the end of the fibreglass tent pole using epoxy resin sold for use on metal. The ferrule was then drilled and a 4mm nut and bolt used as extra security and for the electrical connection to the whip.
(Click on any image to enlarge)
|The tapped ferrule||Ferrule + whip|
|Completed T piece||20m + 30 coil|
Supporting the two arms of the dipole in the centre required either a strong T piece or a piece of aluminium angle as used by AE5JU. Although that would work it required assembly of the antenna each time which is not as convenient as either screwing together platic pipes or using the commercial Buddipole.
Just as I was looking for a solution I found some black plastic conduit T pieces that had been removed from an old milking parlour. At first they seemed ideal for the job with a short length of half inch aluminium rod through top of the T for the dipole arms and a painter’s pole adaptor in the bottom. The idea being that the two arms would be in balance which would reduce the stress on the top of the T piece. On the initial test that worked well but the weak point was the connection between the end of the painter’s pole adaptor and the bottom arm of the T piece. Added support was provided by plywood inserts to brace the top halves of the T piece. These were glued to the plastic using more of the epoxy resin. The result if not pretty but it is strong!
Connections to the arms of the dipole are made to the T piece by PowerPole connectors with short wire tails soldered to a PL259 chassis socket. The first tests showed that the dipole could be adjusted to work on 10m, 12m, 15m and 17m by varying the length of the whips. For 30 and 40m some loading was required. Initial tests with black connecting wire wound 1.5 inch plastic pipe showed that it easy to achieve resonance on both bands.
The coils and wiring need to be completed for final testing. Then the field tests begin! Watch this space.