Wednesday, May 29, 2019

The inverted-L

One of the simplest antennas for the lower HF bands is the humble inverted-L. Take a pole, run a wire up it and tie its end to another support 20 or 30 metres away. It's fed via an antenna coupler (such as a pi or L-network) at the bottom. Clip onto a nearby metal object for a counterpoise, preferably via a ground tuning unit. Then you're on the air, with contacts possible on multiple HF bands. 

It's great if you want to work anyone - near or far. In that regard it contrasts with entirely vertical antennas like the ground plane or tee that are great for DX but not your middle distances just beyond groundwave coverage. Hence you might pick an inverted-L for a field day, national parks, SOTA or local net operation.  Whereas a ground plane might better suit DX operating. 

The Inverted L has been my preferred antenna for portable operating due to its simplicity. Lengths are not unduly critical. But on the lower HF bands if you want vertical polarisation handy for DX performance make as much of it as possible vertical. Or if you want a mix keep it at about half vertical and half horizontal. But don't worry if your supports are low and about two-thirds is horizontal - you will still get contacts. 

A total wire length of near 1/4 wavelength on the lowest frequency of operation can work if you have a good ground. Otherwise nearer 1/2 wavelength is better.  However exactly 1/2 wavelength means extremely high impedances. That can present high  feedpoint voltages and difficulties with some antenna couplers.  So you might want to go a few  metres longer or shorter than 1/2 wavelength to avoid these extremes.

A bit over 20 metres is a good general purpose length for casual operating on bands like 40, 20 or 30 metres. Although I'd suggest (say) 35 or 45 metres for better results on 80m.  

There are thousands of happy inverted-L users around the world. Read about (or watch) some of their experiences here:

* W4RNL's all band inverted L
* The Inverted L antenna and NVIS 

You're invited to comment below if you've had experiences (good or bad) with the inverted L. 

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1 comment:

  1. One of my all-time favorite antennas has been a 120-foot wire with about 35 feet vertical and then the remainder horizontal, suspended between tall trees. I work this wire against 30 wire radials on the dirt with those radials each being about 30 feet in length (not critical). At the feed point I have used an auto-coupler that will give approximate 50-ohm feed point for coax running back to the rig. Using one of these as a portable antenna with battery-powered 100 watt ICOM transceiver I worked from a state park in rural Wisconsin both St. Helena Island (south Atlantic) and Kiribati (south Pacific) with solid sig reports from each. Also regularly work stations on a 20-meter SSB net coast to coast daytime.


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