Hi Rob,
yes having fun - built the 5-band version I was talking about (20,17,15,12 10m) and it works well. Worked into W4 with it yesterday on 10m and 15m. It was interesting that I rounded up the lengths given, to give me some tolerance and the only band that was off was 12m and that was short and I had to replace it with a longer section on each side. All other bands were 1:1 on the frequencies I wanted in each of the bands, without having to change their lengths at all! It was lucky that the amount I rounded up must have compensated for the wire I was using (jaycar (Australian electronics supply chain of shops - like Radio Shack in the US) connecting wire). I calculated using wire with thin insulation (94%) but going back and looking at the lengths that were resonant, it seems that this connecting wire has the same characteristics as tubing (i.e. 97%). I have now added the 40m extensions and will put the antenna on the analyser again tomorrow to see how close it is and trim the new extensions if needed, then go back and check each band in turn.
Al in all a great little tool! The fact that it gives a visual representation of how one side of the antenna will look is great as well.
By the way, in case someone else is thinking of building one of these antennas, I used a spare bit of plastic for the centre conductor and connected the coax and the dipole ends using electrical connector block, the link supports and links from a plastic security chain and the electrical links are 2mm Radio Control power connector plugs and sockets, which I find far superior to crocodile clips.
I suspect the difference has more to do with end-effect and the proximity of other antenna sections/connectors than with the type and thickness of the insulation - but it’s just a guess. Somebody else has said that this business of building wire antennas is not rocket science - it’s basically a process of dividing one number by another to get the length, add some more, then string it up and cut to tune. What’s interesting is how such an antenna performs on the hill. Just my $0.02 worth…
Also, I’m always very wary when I see 1:1 in a SWR meter - I immediately begin to suspect something ain’t right somewhere !
Hi Rob, The 1:1 (which in most cases was actually 1.1:1 or 1.2:1) was on the antenna analyser, not just a swr bridge, hence I could see where the antennas resonant frequency was.
Agreed, surroundings will have an effect with the lengths and I’ll know for sure when I run this on my planned Christmas Day (25th Dec.) activation of Eisenberg in Allgau. I was amazed that I only needed to adjust one section though - I’m not normally that lucky!
One other quirky effect was that after putting in the longer 12m sections, when I wanted to test that 12m was now OK, I forgot to link one side, and the antenna showed as nicely resonant on the 27MHz CB band!
73 Ed.
P.S. haven’t got around to checking the 40m extensions yet, high winds here at the moment - hopefully get to it tomorrow.
!