Sunday, October 21, 2012


Today I finally managed to get round to doing the second part of the experiment with the vertical beams which I started last month.

After the limited success with the 2 element model, I decided to continue with the model suggested by Dave HK1A and make the 2 element into a 4 element by adding two directors. Director number one was tuned for 29.640 and director number 2 for 29.930. Element spacing was 2.07m approx between each element.

Having already done the 2 element version, making the next two elements was a breeze and pretty soon the antenna was up and playing. SWR with the 4 elements gave a good curve although resonated a bit high up the band at around 28.7 MHz.

As in the previous experiment, I did A/B testing with the same reference antenna as before, the quarter wave vertical on the car. Today, the band was mostly open to the states and I worked numerous stations who were kind enough to give me reports on the two antennas. In the previous tests, stateside stations were mostly a bit better on the quarter wave. Today, the stations closer in (east coast) did not notice much difference, some giving a slight edge to the quarter wave and most noting no difference or the beam one S unit better. On the midwest to west coast stations, there was generally more difference in favour of the beam, up to 2 S units in some cases. When N6HD in Los Angeles suggested that propagation was strange and he was getting EU best over 90 degrees instead of the normal 30, I moved the antenna a bit further south and signals improved very slightly on that path.

In summary, the 4 element antenna did not give the improvement I had hoped for, but it was not worse.

There was one case which had me particularly curious and to which I don't have an easy answer. I was called by EA5KV when he was beaming south. I was beaming east, at 90 degrees to him and he logically heard me better on my quarterwave than on my beam. On my receive I noted the same. However when he called in a bit later, with his beam pointing at me (north) there was a very considerable difference in favour of my beam. Does anyone have an explanation for this? He was located about 15km from me and using a horizontal ultrabeam.

The final test will be to use the four elements in a 2 x 2 phased array to see if this gives an improvement over the straight 4 element vertical yagi. Stay tuned!

1 comment:

ON2TD - Tommy said...

Noticed the same this afternoon ! Worked 10 meter FM like it where neigbourhs but indeed had to turn the antenna almost 90° out to get the best signals.