40m Linear-Loaded Dipole

I stumbled-upon this antenna design whilst searching for something resonant, but not too lossy for 40m working.  The garden here at PZT Towers is 50ftx20ft so a full-length flat-top dipole/doublet to get me onto 7MHz was out of the question… Or was it?

What No Coils?
The method of “linear-loading” is a fancy way of saying “fold back on itself” – It reduces the overall length of an antenna without resorting to loading-coils.  The performance is still good, so ideal if you have a small garden or want to try experimenting with bits of wire.  Not only can this type of dipole be used horizontally, you can also use it in an inverted-v or sloper formation – perhaps as an 80m/160m version?  The overall length of my 40m version is 12m / 40ft for the 40m band.  27.8m/91ft should work for 80m but I’ve not built one, so allow for extra wire-lengths, just in case.

The wire-length on this 40m version is actually about 12m per leg.  The spreaders can be made from any non-conductive material such as PVC conduit pipe or you can use ladder-line and make the whole lot from 1 piece of cable.  I’ve since been able to buy a stash of 15mm wide clear acrylic pieces in 50mm, 100mm, 150mm and 200mm lengths which make great spreaders – once I’ve drilled all the holes!  They are also less visually intrusive than the conduit.

The diagrams below give you some idea of how the wires can be kept parallel and supported at each end.

You MUST keep the wires parallel – so use a good gauge of wire (I used a 100m reel of 1.6mm, from CPC for about £8) – I suggest using the following method of keeping wires fixed when using PVC spreaders – Simply drill 4 holes: A pair straight through and then 2 in-between.  The wire is then threaded through to form an Omega symbol.

    

The idea for this aerial came from this website

Does it work?  Oww yesh!  As well as the usual inter-G and continental daytime contacts, I’ve worked the USA and South America during the night – and it’s only 15ft off the ground.  Of course, never being satisfied with what I’ve got, I have since modified it into the Ramsay Fan Dipole.

As heard on the ICQ Podcast, episode 202