Cushcraft A3S Modified For 17, 15, 10 Meters

An attempt to use a tri-band yagi on the 17m WARC band instead of the 20 meter band for which it was designed is successful. This project proved that an A3S will work on 17 meters without any modifications to the traps and only needs changing the length of the tip pieces. Today the balun was installed and the antenna went up after final tuning. It works quite well upon initial testing based on one contact.

The antenna farm as it stands today buried in a lot of smoke from a distant fire. The modified A3S is on the right.

First contact was with Estonia on 17 meters. Yay. Here are the analyzer screenshots for each band giving a first look at how well the modified A3S measures.

Ten meters was not modified so one would expect this band to look good and it does. The Cushcraft dimensions were used unaltered. Below 2:1 SWR for the entire band. That’s an admirable accomplishment for such a large band. SWR for FT8 is 1.21. Great. Ready for Sunspot Cycle 25.

Likewise, 15 meters was kept according to the original Cushcraft instruction manual dimensions. It works well as expected, SWR of 1.37 at the FT8 frequency and below 2:1 for the entire CW portion. SSB will be a problem with this antenna. Fortunately most SSB will be stateside rather than DX and that should be ok.

The 17 meter band is the nut that was sought after and it has paid off. SWR below 1.2 for the entire band and 1.14 at the FT8 frequency. Ahhhhhh. Good feeling. It is now proven that a A3S can be modified for 17, 15, and 10 successfully.

The tips were removed on the driven element and reflector and replaced with much shorter pieces of about 12″ each. The director had the tips removed and no replacement tips were needed. On the driven element and on the reflector tuning for resonance on 17m with the replacement pieces was all that was required. Note that the reflector was tuned 5% lower than the driven element per accepted yagi design. The standard trap resonance of 20 MHz is such that 17m does not interfere or cause any interactions and works perfectly. This is a winner.

Currently the antenna bearing is fixed on Europe because there is no rotator installed. Next upgrade project will be to add the rotator.

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