Tuesday, January 24, 2012

OCF/Windom Antennas

I thought I would take time to share my HF antenna experiences since I am very happy with the antenna I have up now.  I built an 80m OCF/Off Center Fed antenna and have found it to be one of the best mufti-band antennas you can use.  Most people are familiar with G5RVs and I think many new hams are steered in that direction as the solution for the best antenna to use for beginners to get them on many bands.  But, after my experiences with the OCF antenna, I think if your requirement is to have a single wire antenna, and be able to work multi-bands then maybe this might be a better choice then the old G5RV.

I built mine using a 5:1 balun, the dipole fed off-center with approx 95ft on one side and 45ft on the other(give a take a few for trimming/tuning).  It's up in a tree with the center hung at about 50 feet, and the ends coming down into another tree on the long side at about 15 feet tall giving that side of the dipole a gentle sloping down, and the shorter side goes down at about 30 deg and tied to the top of a 6 foot wooden privacy fence.  It is fed with about 80 feet of LMR-400 Coax with about 60ft of that underground in the yard going out to the base of the tree in the corner of the back yard.

When I first started out, like many one of my first antennas was a 80m G5RV, it worked ok but it required a very good wide range antenna tuner such as the LDG I had at the time just to get it tuned to be usable.  Now I don't need an external tuner at all, and the simple internal tuner in my FT-450 can tune nearly every band to 1:1 with ease. In fact chances are that you could work this antenna without any tuner at all in some cases, the SWR match is quite reasonable on most of the bands.  I know that SWR is not the end all of antenna performance measurements, but it helps.

Here is a plot from my antenna analyzer:




You can see its 2.1-3.0 on 80m, 1.5-2.0 on 40m, ~4.0 on 30m(too high for my internal tuner), <1.5 on 20m, ~2.25 on 17m, <4.0 on 15m, <1.5 on 12m, and 2-3ish on 10m, its also 2-2.5 on 6m which is not shown on this chart.

Compared to my first antenna which was a G5RV, which had many bands with SWRs in the 5-10+ range, this antenna seems to be much less work to tune and a better all around multi-band performer.


I am not going to try and say that this antenna will save the world, but I do think it's worth thinking about if your goal is like mine to try and sneak in one good multi-band wire antenna in a restricted neighborhood back yard.

1 comments:

AD4C said...

I have been for many years using Windom antennas, have used 4 to 1 and 6 to 1 balusters with same results, always sir less than 3 to 1 in all HF bands. Right now I built one for 20 to 10M, and is very efficient on any of those bands.
It's a perfect choice for multibanda wire antenna.

Hector
AD4C


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