[ADXA] Woof woof (silent woof)

[Stan Stockton]


Jon,

I see this morning that Pat responded to your message which reminded me of having saved a response i was writing in drafts when I answered a phone call yesterday morning.

Some questions:

Am I understanding correctly that the numbers you listed below represent the SWR at the low and high ends of the bands?  Does the SWR look good anywhere on 20 and 15 meters?  What is the highest SWR you see on 10 meters?  What is the coax type and length to your analyzer?

It would be good to see what the SWR is every 50 kHz on each band to have a better understanding of what you have.  For example, if you said that the worst SWR on 10m in that frequency range was 1.75 I would say you might be measuring the antenna with a very lossy coax cable.  It is not possible for a small 3 element trapped antenna that has any gain to have that good of an SWR curve over 1.7 MHz.  

In the manual I found, they claim SWR under 2-1 for greater than 500 khz but do not specify which band or bands.  The only one that could possibly be 2-1 or less for 500 kHz would be 10m - but not 1.7 MHz, not possible.  They are also claiming 8 dBd gain which is equivalent to 10.1 dBi free space gain - within an half dB of what you would get with a 5 element 20m mono band Yagi on a 48 foot boom….

In my opinion the antenna needs to come down.  If all the dimensions are correct you should see what they claim for SWR with the antenna pointed straight up with the reflector off the ground by about 10 feet.  If you do not see a reasonably good SWR on each band you have one or more bad traps and/or have not assembled it correctly.

If you were to start changing tip lengths of parasitic elements in order to achieve a better SWR you are losing gain and pattern.

Whatever you do, be careful when working on a tower.

73…Stan, K5GO



> On Jan 10, 2026, at 10:41 PM, Jon W. Reynolds via ADXA <adxa at mailman.qth.net> wrote:
> 
> Long Tower Saga update:
> 
> 2 out of 3 woofs (I'm guessing). The Saturday tower fairy came out and we were able to accomplish much more work on the tower project! We now have a rotor that turns the antennas from the shack!
> 
> We still have a little bit of work to do in the tri-band A3S. Because I'm new to tower work,  I prioritized things a little backwards. I got the antenna assembled and up (while the help was in town), before I checked the swr, and it is a little off. I also tried not to crimp the antenna boom with the u-bolts, and they are loose enough to sway a little. So...there is still some work to be done, but I have the rotor system up and working.
> 
> The SWR Readings as I show with the Amazon nano vna:
> 
> 20m 14.000-14.350
> SWR 3.77-2.61 wedge shape (high to low)
> 
> 15m 21.000-21.450
> SWR 3.45-3.68 slight wedge shape (low to high)
> 
> 10m 28.000-29.700
> SWR 1.13-1.75 (slight wave shape)
> 
> My plan is to suspend the antenna from above on the mast pole, unbolt the antenna from the mast, and rotate it to 90° so that I can reach the loose elements. I'm thinking to address the swr problems, I'll extend the tips of the of the reflector and driven element 1/2" and re- mount everything and check the results.
> 
> I'm open to suggestions if anyone is forthcoming with knowledge/technique or experience with a cushcraft A3S and tuning it a little.
> 
> 73
> Jon
> KI5UCZ
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