Comudipole

Over the past weeks, I've been busy, on and off, helping get a new licensee up and running on all bands, and pretty much all modes, from 80m to 70cm.

The HF side is always difficult to settle upon in terms of antenna choice.  But, for all-round performance, relatively modest space requirements, very low visual impact, and extreme wind tolerance, a simple wire dipole is hard to beat.  It's also cheap: even if you buy a balun, the antenna only cost about £55 or so.

I recommended my friend use the Comudipole - or doublet - arrangement, which is very easy to set up.  Another ham had earlier made up a coax-fed dipole of galvanised steel wire for him, but the losses for a non-resonant, multiband dipole like this are unacceptably high for coaxial feeding.

Simply by dumping the coax and replacing it with 300 Ohm twin fed to a 4:1 current balun (for speed, we bought a G-Whip commercial unit, but it's easy to make your own), the dipole can be used with inconsequential losses.

I'm not a big fan of steel wire, but it does seem to work pretty well, and has an advantage in that one can really rack-up the tension on it to avoid sagging.  All the same, I'd always choose a non-magnetic, copper wire for my own work.

I was very happy to see that the comudipole matches up with my friend's internal ATU on his FT-450D with no problem at all on all bands from 80m to 6m.

Here is what the SARK-110 antenna analyser makes of it in a full HF sweep:

The 80-10m Comudipole HF sweep. It also matches nicely on 6m.

Some of those SWR values might look awful to the uninitiated.  But, remember that SWR is, of itself, a lossless phenomenon, and that the losses in the 300 Ohm twin are only a fraction of a decibel - much lower than the same antenna fed with coax.

I'm glad to say the practical experience of using the comudipole is very good, and my friend is very happy with the speed and efficiency with which he has come to be on the air.  I'm glad I chose this antenna for him, and relieved it all came together with no problems!