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Appears in this configuration I actually built a Sperrtopf antenna. Difference being Sperrtopf is fed through bottom, (easier to experiment) where as Topfkreis feeds through side (get it right the first time). It's working really well.

Check this out. Think I'll hook it up and give er a shot. Lol and holding the ground to the tube with my thumb.

Not sure about any of that as I'm very new to this but it appears the inner diameter of the (1/4 wave) outer tube (D) to the outer diameter of the (3/4 wave overall) inner tube (d) should be as close to 50 ohms as possible calculated the same as coax cable. Only info I can find shows formula...

Antenna. I stumbled onto the design looking at J-poles and was intrigued. Internet search of topfkreis antenna shows a few results.

Man this one is a challenge. First attempt was resonant at 375mhz. I just learned about K factor, made some adjustments, closer at 410mhz now. I think the feedpoint is throwing me off at this point. I've modified it to be temporarily adjustable. I'll get there...

Found some 1/4 and 3/8 OD and 1" ID copper tubing. Shined up nice. It'll be my first attempt at a Topfkreis build. Hoping I can get that impedance close.

Updated version and the resulting sweep.

Still had to trim it, then added a tail to the reflector. Not afraid to admit no clue as to what that does but it made the Smith chart happy and this little rig just had a good contact on a repeater 28 miles out on that little Retevis and me holding the antenna inside our living room. 3 degrees...

I had good (lucky) success with an 11 meter version I built and I like the 50 ohm feed but yeah, a yagi might make more sense. I'm just having fun building these. I have no formal education on this stuff but I can follow directions. The nanovna sure helps.

I'm a little slow and just noticed the vertical polarization I referred to is for the eznec model and has nothing to do with dimensions. So moxgen and the online calculator are showing different results. Hmm

Thank you! The link you shared has indeed been the closest so far but my results differ. I suspect it's because you were able to choose vertical polarization (thank you). I'll be using the specs from your results but for comparison, here are mine.

I'm having a heck of a time with the online moxon calculators and can't get moxgen to install on my old linux system. I'm using insulated solid 14AWG. Thanks in advance.

1/2 over 1/2 over 1/4. Not sure why I had to lengthen the top element but it sure works good. Also bent the radials down a bit to get the impedance right. Hooked it up to my little Retevis RB27 and made it out of our basement to a repeater 13 miles away with multiple structures in the path. I'll...

A local I talk to also made a J-pole out of 1/2 copper and it worked out really well. He's got it about 40 feet up. I just finished a collinear antenna I'll need to house in something but I heard pvc can detune an antenna.

One thing that's really nice about UHF, the small antennas. Made this little guy the other night. Fun to watch the impedance change with height above ground and nearby objects. VNA sweep is with antenna about six feet above ground outside. Calibrated at the feed point. Able to hit my usual...

Happy New Year from St Clair, Missouri!

Our four children all chipped in and got dad a NanoVNA H4 for Christmas! What a great tool. I tested all of my mobile antennas yesterday and each one needed some fine tuning to get spot on. I calibrated at the feed point so the NanoVNA was only looking at the antenna. I'd never studied Smith...

All I want for Christmas is to move into our new property and get a proper antenna up in the air. Have a great day!

Common mode choke. First one I've ever used. Really cleaned up my receive.

Box stock President McKinley in dash barefoot into about 13ft of RG58 with 8 turns around an FT240-61 core at the feedpoint of a 3" Breedlove NMO mount drilled through the roof of my Cherokee. Fat braided cables bonding hood and exhaust. Larsen NMO27 or NMO30BCO coil with 64" whip for mobile...