Efficiency and small size on Topband?

The only thing between me and 9B-DXCC is 70 countries on Topband and, as you might expect, 160m has been on my mind a lot lately as I ponder the upcoming season.

In fact I’ve just ordered the parts for the following antenna.

When the May/June issue of NCJ Magazine arrived a couple of weeks ago, one article jumped out at me and smacked me upside the head with deja vu. Where had I seen this before?

The article (by Guy K2AV) was about a unique way to build a 160m vertical or inverted L with a ground system that fits on a city lot and offers efficiency not normally associated with compromise designs. As I read the article, it became apparent where I’d seen this before – on W4KAZ’s blog.

From Guy K2AV:

There are NO radials.  The main design point of the antenna is to minimize lossy currents induced in the dirt and confine TX signal current to the FCP and the radiating wire.

A cruise around the internet with stops on the Topband reflector and the website of W0UCE yields a lot of info and offer nothing to disuade me from trying this antenna myself. And, as I mentioned above, the timing is perfect.

Many tall pines were removed from the property earlier this year due to Texas’ drought, but 20 tall & healthy ones remain, with 15 of them being 85+ feet tall. As luck would have it they are ideally suited in terms of placement and the trees that were removed would have been in the way. To every cloud, a silver lining…

But back to this antenna, the keys of which are a folded counterpoise and an isolation transformer.

A lack of adequate space has always prevented me from any serious efforts on 160m. Contrary to what many advertisements would have you believe, a vertical is not a space-saving antenna due to the RF ground system necessary for efficient performance.

The folded counterpoise for the 5/16-wavelength inverted L described in K2AV’s article is only 66 feet long and constitutes the complete RF ground - something most HF-active hams can easily manage.

Using the Reverse Beacon Network as a method of comparing this antenna with some other type at various QTH’s gives promising results which show themselves in real dB values as opposed to “human optimism”.

The best description of this antenna (with plenty of drawings) is at the website of Jack W0UCE. Guy K2AV’s article in NCJ provides a technical description and is available as a pdf file here.

Tom DL2OBO has recently built an 80m 4-square using an FCP as the RF ground for each vertical comprising the 4-square. You can read his description (and hopefully future results) here.

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  1 comment for “Efficiency and small size on Topband?

  1. May 18, 2012 at 11:55 am

    I am very happy with the FCP system. It sounds like it might suit your QTH also.

    The bad news here is the wind from the latest round of thunderstorms on Tuesday knocked the vertical out of its biological support system(a big poplar). A branch broke, taking out the Inv-L support rope on the way down. The poplar is almost as bad as a pine for shedding branches, but it happens to be in the perfect spot.

    Now the challenge is to get a line back over the branch, I hope before WPX. One of those pneumatic spud guns sure would be handy here. I’m sensing a blog rant(…er “post”)…..

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