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Pollenating the Antennas – Crossed Dipoles on 40m and 20m

The tree pollen is really flying now. It is thick enough that it looks like a light snowfall or a misty rain when seen with the sun at the right angle. (Ahhhh-CHOOO!)

Pollen must be good for antennas. Two new ones sprouted up over the past weekend on new lines I shot into the biological supports before the kids’ spring break from skool.

I somewhat reluctantly packed up the 15m/10m nested rectangular loops. The support was just too good a height(about 15m/50 ft.) and location to leave it being used on relatively unproductive bands. In its place there is now a 40m dipole that favors the NW/SE directions. A bit of tuning around the 40m band doing A/B comparisons between the new dipole and the old NE/SW dipole showed promising results. The new dipole is much better into 8-land and 9-land. The old is better into 2-land and Europe. For some reason most of FL seems about the same on both. Interesting.

The differences on rx signal strength is more than I expected in a lot of cases. It makes little difference for strong signals, but a lot of difference on weaker signals. Hopefully this will help add Q’s to the contest logs. It also is a bit of commentary on the non-linearity of S-meters.

The antennas are at an almost perfect 90 degree angle to one another. They do not actually cross one another. Looking down from above they form an L shape with the south end of the NE/SW antenna pointing towards the eastern most tip of the NW/SE antenna. Modeling showed ther was little interaction between two dipoles in that configuration, but it seems likely they are not completely invisible to one another. I’m happy with it so far.

40m turned out so well I decided to do the same thing for 20m. The new NW/SE 20m dipole may be somewhat less productive, but maybe it will help to bag AK and NT and BC in the domestic tests. Unlike the 40m pair, these two antennas definitely show a difference in coverage into FL. Over the weekend there was one FQP station that was in the noise on the NE antenna, and peaking at S-5 on the SE antenna. (More S-meter non-linearity?)

The lesson learned here is that a single fixed dipole is leaving gaps in the coverage. The solution is simple. If it is practical to do so, adding a second dipole at 90 degrees to the original will definitely help fill in the holes. It’s not as good as a yagi, but better than a single fixed dipole. A rotatable dipole would also do the job if you remember to turn it. Note: switching between dipoles is a lot faster than a rotator, but coverage is less continuous .

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