Saturday, 17 September, 2005

A new HF antenna

When I passed the exam for my General class amateur radio license I started looking for ways to put up an antenna for long distance, high frequency (HF) communications.  Although I have a lot of property and few neighborhood restrictions, I am limited by budget and aesthetics.  Lack of funds means no towers, and aesthetic considerations prevent me from stringing wires all over the place.

I decided on a 40 meter horizontal loop built out of #14 copper wire and attached under the eave of my detached garage.  This isn't a particularly efficient antenna, especially when fed with 150' of coax, but I've managed to make contacts all over the U.S., Canada, the Caribbean, South America, Hawaii, and even Australia.  The antenna seems to work reasonably well on all of the HF bands above 80 meters.  I've used it on 80 meters but it's not very good for that band.  Horizontal loops do not perform well below the design frequency.

The most common HF antenna used by hams is probably the half wave dipole because it's easy to build and erect, and a pretty good antenna even when installed low to the ground.  Understand, a half wave at 40 meters is approximately 66 feet, and the ideal installation would have the antenna at least that high off the ground.  We have some big trees here but they're not that tall.  Still, one does what he can with what's available.

My 40 meter half wave dipole consists of two 33-foot lengths of #14 insulated copper house wire connected to a center insulator and strung between two trees at a height of about 30 feet.  The hardest part of the entire process was pulling the antenna up into the trees.  Because I wanted to hide the antenna as much as possible, I ran the wire through a third tree and snaked the coax feed line up that trunk to the center insulator.  With the exception of a 20 foot span over the garage, you can't see the antenna in the trees.  It'll be interesting to see what it looks like in the winter.  In any case, I didn't post a picture because the thing is terribly difficult to see.

All I can say right now is that the antenna works.  I've used it to talk with hams in many different states but I haven't had enough experience with it to say how well it works.  The antenna is oriented roughly west southwest (bearing 240 degrees from tree 1 to tree 2) so in theory my best performance will be towards 330 and 150 degrees:  northwest U.S. and western Canada, and the Caribbean.  Time to experiment.