Saturday, May 25, 2013

Latest EFHW antenna


It has been too long since I have posted. A little busy with life and work, but that is no excuse. I do have the latest incarnation of my favorite antenna, the end fed half wave done and ready to put on the air. Had I actually had my brain in gear in the first place, this would have been done a lot sooner. As it was I did the brute force approach, which was cut a separate wire for each band. In retrospect, this was idiotic. The much better way to do it was done by Ed WA3WSJ when he made his Iditarod Dipole http://wa3wsj.homestead.com/iditarod_mini__dipole.pdf  Ed uses snap swivels and spade lugs to connect more wire sections to the antenna to change the dipole frequency.
DING DING... Pay attention Bob!

The main reason I hate dipoles and really like EFHW's are that dipoles need to be pulled up on the center, and each end. Don't get me wrong, the dipole is a superb antenna, I just hate having to raise the dang thing. The EFHW works well here in Washington State as we have an abundance of trees. I connect a quarter inch thick steel washer to end of the wire, swing it around three times for luck and sail the wire over a branch. The antenna is up in seconds.

As you recall, the counterpoise for the EFHW is .05 wavelength. So, for 20 meters, the antenna wire is 33 feet, the counterpoise is 3.3 ft. Easy math! At this point I will refer you to an earlier post for how I make my EFHW tuner.  http://eggsandhamradio.blogspot.com/2012/06/end-fed-half-wave-antenna.html

Here is the antenna wound around some corrugated plastic, which is my favorite material for lots of things in the shack. In the picture also is one of my EFHW tuners.


When I measured out the wire, I used 468/Freq to get the half wavelength. From there you need an antenna analyzer to nibble the wire down to tune where you want best SWR in the band.

What I did for my antenna is as follows:
15 meters was 22 ft of wire and 2.5 feet of counterpoise
To add 17 meters, I connect roughly 3 feet more to the 15 meter antenna, same counterpoise.
To add 20 meters, I connect roughly 8 more feet of wire to the 15/17 meter antenna, same 2.5 foot counterpoise.

I somehow messed up cutting the wire and was a tad short so the 20 meter wire resonated in the SSB portion of the band. I then cut a 15 inch chunk of wire to add in for the CW portion of 20 meters, removed for the SSB portion. This mistake actually now seems to have made a better antenna, I now have an excellent match in both portions of 20 where I like to operate.

73, Bob