How to enhance DX vs NVIS using the Alpha HF JPole antenna.
I had issues with the 75-foot J-Pole not performing well when compared A/B to my G5RV on the local nets. I hope my story provides insight to others who might be experiencing similar issues. A call to Alpha Antenna provided me with an installation change/suggestion. At first, I figured the J-Pole simply wasn’t working. My main issue was that the net operator just 180 miles away read my signal as only half the strength as my G5RV. I can also state that the G5RV provided a better transmit & receive on DX. Alpha’s suggestion was based upon their premise that the majority of power on end fed antennas is radiated from the first 30% of the antenna. As it turns out, feed point placement is critical to the performance of their antenna.
I not only had the feed point too close to my gutter, but all of my antenna under the eve of my roof. Basically, all of my signal was being absorbed by the gutter and house.
Once I moved the feed point about two feet higher than the edge of the roof and kept the rest of it free of obstacles the net control operator said he couldn’t tell any difference between the G5RV and the J-Pole.
I still had another issue with the J-Pole though, which was the DX performance wasn’t nearly as strong as the G5RVs. So, one more call to Alpha Antenna was made. This time I talked to the owner, Steve, who nailed what the problem was with only a short description of my issue.
Turns out that when the J-Pole is installed flat-top the NVIS is accentuated, and DX is reduced. Makes sense now that I see it in practice. Anyways, Steve said that if I wanted to maximize the NVIS and DX performance of the J-Pole, then I should install it as a sloper with the feed point at the highest apex. With both of my problems solved, I rate their antenna a 4.5 because it took some work to make things happen in the manner, I expected them to.
W1WI
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