Thursday, May 30, 2019

The Continuing Saga of The Antenna....Now With Pictures!

So in between playing Grandpa and installing the new weather station, I did manage to get some (undocumented - gasp! -) antenna work accomplished, both on the end-fed random wire, and on the 20 Meter BuddiStick replacement. The BuddiStick worked extremely well, but I didn't consider it to be an "all weather" antenna, so I took it down during windy, stormy weather. I just couldn't see letting that Really Cool shock-cord whip get turned into a pretzel.

On the 88' end-fed, I wound up removing ALL the counterpoise radials, exactly "As Advertised", and it works acceptably well on all bands except 75 Meters (3.5~4MHz), and 60 Meters (5 "channelized", shared frequencies at ~5.5MHz). I took the radials off in stages, sweeping and recording the antenna response each time, and the "best" it got was with a single 7' wire off the ground connection. I could raise the center another 6', but I really don't want 3 sections of mast on the ends. I'm just afraid it might get 'whippy' in the winds we have here and come down like the Tacoma Narrows bridge did. I might change my mind after I get the new post installed for the fed end, and have a much more substantial mount for the mast, but for now, this is about as good as I think I can make it work. Took me a while to shift-gears, and think about the specifics of deliberately NON resonant antennas, but now I understand why that particular class of antennas can be quite 'counterpoise independent'. What I had ingrained in me about antennas was 90% resonant antennas, and it's wrong for these antennas. So it was a valuable learning experience to understand this new critter, and proves an Old Dog can learn a few new tricks when properly motivated.

And I finally took down the BuddiStick tripod which has been out there for about a year now. Even though the "final" version of what is now called the "20 Meter Vertical" is sketched out, there comes a point where I put the hardware I have together, and test it out. Then I use it, experiment with it, and modify it until I figure it's pretty much optimized for what I have to work with. For now, it's mounted on the 5' tripod and section of mast that my original Davis weather station was mounted on. The curves are "text book perfect" for a 1/4-wave, resonant antenna, and I'm quite pleased, even though my meticulously calculated element lengths appear to be an inch or so too long. Better than too short! It's a simple matter to loosen a hose clamp, slide a section down an inch or two, and retighten the clamp to change the resonant frequency, but that could shift again if I move the antenna. Anyway, it never exceeds 1.5:1 VSWR anywhere in the 20 Meter band, so getting it 'smack on' @14.150MHz is easy to do, but not strictly necessary.

Pix of the aftermath.....

Weather station off the tripod and ready to rebuild. I was going to replace the white plastic OEM enclosure with a plastic junction box from HD, but after examining the damage, I can just glue it back together with some JB Weld, and paint it to slow down any further degradation.



Here's the new vertical on the former weather station tripod. I'm going to put a few guy ropes on it later today.


Yes, it's "Pebbles Approved"! The branch is from the crabapple tree. Once it dries out, I'll strip the leaves and twigs from it, cut it up, and we'll have a bit of hardwood to toss on the fire.

Truly a gorgeous day outside today.

This the feedpoint assembly showing the coax-to-studs box I made, and the line isolator coax choke I threw together last night. The coil of coax adds some "Common Mode" isolation between the feedline and antenna. If you don't use something like this you'll get currents on the outside of the coax shield, and it can cause Funny Things to happen.


The five books I've been pouring over on antennas, transmission lines, and baluns really helped me understand a few things I was more than just a bit hazy on, and solidified the differences between resonant and non-resonant antennas for me. They're both antennas, but quite different in how you feed them, and what you see when you measure them.

This is the VSWR curve for the vertical.

Pretty damn flat!

But will it help get us off the island, Professor? Well, maybe, Gilligan, if propagation is good.

I'll find out both answers this weekend, as it's Museum Ships Weekend, and I'll be on 20 Meters trying to contact as many Museum Ships as I can. The Iowa, New Jersey, and Missouri will be on-the-air, but the Wisconsin is MIA again. They have an Amateur Radio club, but they're not very active.

The USS Nautilus is supposed to be on, and I'd really like to contact them.

4 comments:

  1. Your vertical looks like a perfect PSK31 antenna!

    (just kidding)

    How does the end fed antenna look now? ISTRC the plots with the counterpoises looked good.

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    1. VSWR on 75 is still >3:1, so the rig can't tune it. It's better on 40 now, <1.8:1, and worse on 10, >2.5:1.

      After I get the 4x4 posts in the ground, I'll just roll up the end fed and store it away. My "real" 88' antenna will have the SGC autocoupler at the feed point, so the rig won't ever see a VSWR >1.5:1.

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  2. And the proof will be in the pudding... so to speak!

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    Replies
    1. So far, if I can hear them, they can hear me. One of the nice things about this radio is that it has 200 Watts output. I never pushed the little K2 much past about 75 Watts, so I now have a transmit signal that's 3dB stronger.

      So far I'm quite pleased with it. I have to tie it down better tomorrow because we have some storms coming in.

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