End Fed Wire Antenna

 
Home Interests Squalo Antennas Tower Two Meter GP I have lived in just about every kind of building you can imagine. I have lived in old apartments, new style apartments, mobile homes, houses, and even an old converted hotel. In each instance, I always tried to have fun with my radio hobby.

One antenna that I have always used with good results was an end fed random wire. A random wire is just any old length of wire that runs from a support to the back of a tuner and fed to an HF transceiver.

                      

I've used dipoles and verticals, but the random wire has always done in a pinch.

The random wire is not without it's draw backs. I have had problems in the past with RF in the shack resulting in "RF bites" from my equipment. This also means interference to and from other electrical appliances. There are ways to work around some of these problems, but the user of these antennas has to realize there are limitations. Sometimes I have been limited to one band for transmitting.

My old set up had been the use of a random wire in my attic. It worked well on most HF bands. However, as stated above, I was picking up every noise you can think of in the attic. TV set, computers, heating and air conditioning, etc. So I was thinking it was time to go outside with my wire antennas.

I could have put up a dipole but I didn't  want any wires going out to the front yard. Besides, the antennas I was going to put up was effectively a half wave antenna like the dipole. The only difference is that the half wave dipole is fed in the middle and the half wave I wanted to erect was a half wave fed on the end.

This is where the similarities between my old antenna and the new one end. The new antenna would be "resonant" instead of just a random wire. And instead of the antenna terminating at the back of my antenna tuner,  it would have a feed line.

           

The new antenna would have a open feeder type feed line. I had some 450 ohm window line that most stations use, so I decided to give it a try. One thing I read about open type feeders is that they are very efficient. That means the losses are very low even when the mismatch between the antenna and feed line are high. However, they are effected by weather and close metal objects like towers or electrical wiring. Spacing the window line from the tower was not going to be a problem, but running it inside was. If it was brought in through the attic, there were going to be a lot of electrical lines and telephone lines near the closest entry point. Not to mention all the ac/heat ducts running everywhere. It was starting to look like I should just stick with a random wire.

Coax has the advantage of being routed into areas of my attic that I mentioned previously. It can be attached to a tower leg and run to the antenna. The draw back is that it would make my antenna a monobander or good on only one band. Coax is also very lossy when you get a huge mismatch.

I had seen online where people made a feed through line of two coaxial cables. These side by side coaxial lines made it where an open feeder could pass through a wall. I didn't find much info on the subject. It is possible to do it, but some losses can be introduced to the system if the run is too long. I calculated my run to be about eight to ten feet, so I decided to give it a try.

The antenna was constructed as shown in the above drawing. As with any new antenna design that gets used at this QTH,  it was mounted at the 20 foot level. I know this is a bit low for an 80 meter antenna but it's a good place to start. Besides, my attic random wire antenna is about the same height.

Unfortunately, the antenna didn't perform as well as expected. There was a slight increase in signal strength on receive, however it was about the same on transmit. So for the effort and expense, I would say this antenna was a bit of a disappointment.

I'm sure if the antenna was mounted all the way at the top of the tower and the other end was elevated the same or higher, it would have performed much better. I also think that the feed system was not up to par. The double coax feed was two 75 ohm TV coax cables with very little shield. Since there was no match to the 150 ohm cable impedance with the 450 ohm window line , signal attenuation was likely.

I think this antenna would still be a good performer if it was fed as in the above diagram. I bought a 4:1 balun that would go between a 52 ohm coax line and the 450 ohm window line. This is a typical set up with an end feed half wave antenna. I haven't given up on this design and will try again in the future.