18-24.jpg 18-24-base.jpg
It’s a good job I rarely throw things out (much to my XYL’s annoyance). Back in the days when we had a viable radio-based DX-Cluster network in Scotland, I had an ex-PMR UHF colinear on top of my main mast. This was ultimately condemned when in 2003, the winch cable snapped and the N-Type connector was ripped off. But . . . I didn’t throw it out . . . and a good thing too! . . .
To insulate the antenna from the mounting bracket, I double sleeved it with two concentric grp tubes, 25.5mm and 31.7mm. The latter fitting nicely between the two halves of what was once the base of the UHF colinear. See figure 5, right. For the feed-point, I adapted what had once been the feed-point of the afore mentioned 10m beam. I opted to leave the bottom end of the antenna ‘open’. I figured that if water was to inevitably ingress above, where the sections interlock, then I’d best leave some means for it to egress.
Fig. 5 - Base.
Figure 6, on the left, shows the attachment of the four tuned radials. These, I made from yet more antenna wire salvaged from the massive wide-band RACAL antenna that I picked up back in 2003. The radials are electrically connected to the base by crimp ring terminals, whilst loops created using mini ‘D’ clamps, allow the radials to double as guys by transferring the strain to the ‘U’ bolts attaching the base to the mounting pole . . . Which is actually 2 of the 3 boom sections from the stricken 10m beam!

The photograph on the left shows my (nearly) nine year old son Mark, holding the finished antenna

I decided that the antenna should be fed via a twin-choke balun so as to minimise feeder radiation. See figure 7 on the right.

The photograph below shows the finished antenna mounted on its pole. A short length of grp tubing acts as an insulator between the pole and the antenna, thus minimising any unwanted resonance.
Fig. 6 - Radials.
Fig. 7 - Balun.
But how does it perform?. . .