ANTENNAS

 

DIPOLES

I started out with a simple dipole of 2x 10 meters that I suspended between the house and a tree in the back of the garden. It was only 6 meters from ground and did not give good results, particularly for the lower bands, it was just too short and too low. High time to take a more serious approach.... I decided to raise the centre of the antenna to something like 10 meters, like an inverted Vee, and use off centre feeding. I could not feed a dipole-like antenna symmetrically because the mast that should support it could only be placed on the front of the barn behind the house. That spot was closer to the house on which the one end of the antenna should be fixed than it was to the tree that should support the other end. I purchased a Fritzel FD3 plus balun. In the barn I had kept a hollow fibre glass surf board mast of some 5 meters long. I extended it for another meter with some PVC pipe and made a base fore it that I bolted to the front of the barn near the rim of the roof. This gave me the desired 10 meters height. I ran coax cable through the mast and to the shack. It worked all right for all bands but 160m, and only with an antenna tuner, of course.

E-H ANTENNA

The Fritzel FD3 antenna did not perform too well on 80m, not surprisingly, so I started looking on the internet for an antenna that would work on 80 but that would only take up limited space. I came across magnetic loop antennas, but these all needed a vacuum capacitor and a suitable tuning mechanism. This was all too complicated for me. This is why I got to the EH antenna. From the various articles I read on the internet I understood that the performance and the operating principles of this  type of antenna were controversial, to put it mildly. Yet I decided to give it a go and built a version for 80m. I installed it on a 3m long PVC drain tube, as can be seen at the right. Quite frankly this antenna had fairly good and interesting looks but its performance was a lot less than good. It picked up quite some QRM and although I received some good reports, i.a. from Belgium, I decided not to pursue this experiment and to revert to normal wire antennas. But before I did so, I would make one last attempt and test another form of EH-antenna on which I had read positive comments on various internet sites, the Isotron.

ISOTRON

At the left is the other EH-antenna I built. It uses, besides copper wire of course, two stainless steel serving trays of about 50 cm in diameter I “borrowed” from my XYL and PVC drain  pipe. In fact this antenna is just a big resonant circuit made up of a coil in the centre plus two capacitor plates at each end of the coil. This antenna also was designed for 80 meters. Its performance as an antenna was a disappointment, comparable to the first EH antenna. Even more importantly, my XYL did not like its looks and, also, wanted her serving trays back. This was all enough reason to take the thing down and stop further experiments with this type of antenna. At parties at my QTH, guests sometimes ask why our serving trays have a hole in the centre .....

HORIZONTAL DELTA LOOP

It was time for some form of a wire antenna again, an antenna that would allow me to work the 80 through 10 meter bands, with an automatic tuner. It would be ideal if the antenna would be symmetrical and if the feed point could be on the front of the house and not somewhere in the middle of the garden. Ideally the feed point would be near one end of the antenna.


Would there be such an antenna? This is how I discovered the horizontal loop antenna. Why didn’t I think of this antenna earlier?  It had all the specs I wanted and it was quite easy to make. I decided to go for a delta loop with the feed point at one corner that I attached to the front of the house at 8 meters height and the other two corners each suspended by 10m high apple trees about 16 meters apart from each other. This gives a triangular loop with sides of 24, 16 and 22 meters plus 2 times 4 meters vertical feed-line along the front of the house, 70 meters in total. At the start of the feed-line I installed a 4:1 balun. From there I ran coaxial cable to the shack, at the other end of the house, a distance of about 20 meters from the feed point. With an automatic antenna tuner in the shack I was able to work on all HF bands.

Part of the thorizontal delta loop; note the vertical open feeder. The prototype loop is held under some tension by springs on each of the two other corners (not visible here). The antenna has survived wind gusts of 10 Bft (many roof tiles did not...)

Construction details of the horizontal loop for 160 - 10m, click on the picture to enlarge....

The dimensions of the loop shall not necessarily be copied, they are the consequence of  the dimensions of my back yard and the position of trees.

The next logical step was to use my MFJ-925 automatic antenne tuner remote, i.e. as close as possible to the loop antenna, but still inside the house to protect it from the weather. This set-up has the advantage that I do not have to tune the 30m coaxial feed cable and can thus avoid the losses that this brings about. Parellel to the coaxial cable I ran a 30m screened CAT6 FTP-cable from my  transceiver in the shack to the MFJ-925 tuner. I can tune the antenna by pushing the “tune’ button on the transceiver. Tuning takes just a few seconds for any band.

This setup works to my entire satisfaction.


Of all wire antennas I have tested, including:

  1. - 2x17m dipole with 10m open wire feeder

  2. - 20m and 40m long end-fed half wave antennas

the delta loop generally works best i.e. one S-point stronger signals on all bands (but 160m) and noticeably less  noise. The delta loop antenna is a keeper!