home Allgemein UHF Ring Antenna – Easy as Pie, round as PI().

UHF Ring Antenna – Easy as Pie, round as PI().

 

ring antenna schematic
ring antenna schematic

A horizontally built vertically polarized antenna..

 

The halfwave ring antenna was first patented by J.M Boyer in 1963 in the US.

Although it looks „very horizontal“ it has vertical polarization!

The circumference of the radiating ring is Lambda/2 so the diameter of the ring

can be calculated as Lambda/(2*PI).

The ring is at one point connected to ground with a given height h of 0,01*Lambda as well as

the feedpoint X has a 0,01*Lambda distance from the ground connection of the radiator-ring.

 

70cm UHF ring antenna
70cm UHF ring antenna

 

In my experiment I started with a 20cm diameter oil can as ground that I fished outh of the waste of the nearby universitiy canteen.

(note: yes, I did this on purpose because I knew I’d one day build an antenna from it)

For my guesswork I chose the repeater input of 431.00 Mhz. The resulting diameter about 11cm did just fit right on top (meaning th bottom)

of my can.

I had all material at hand so I didn’t pay anything. From my guess the cost of all material is less than 5$.

tools I used:

  • heavy duty soldering iron
  • soldering wire
  • bending iron
  • sandpaper

material I used:

  • coax with connector to the radio
  • large food can
  • thick copper wire (the ones used for grounding purpose)
  • tuning capacitor (totally overrated because you can just bend the ring away or towards the direction of the ground to influence the resonance frequency.

time used for buliding and calculation: 20 minutes

 

ring antenna feedpoint
ring antenna feedpoint

Building instructions:

  1. Cut the radiator wire about 20% longer than calculated.
  2. Roughen the food can surface with sandpaper for a firm solder connection.
  3. Bend a little foot with the bending iron to the radiator to provide a mechanically – solid solder connection.
  4. Put a solder puddle on the roughened can surface as well as pre – solder the radiator’s foot
  5. Solder the radiator to the can. (At this time it will look like a normal vertical..)
  6. Use the bending iron to cerate the angle h and form the ring and solder it to complete the circle.
  7. Connect the coax feedline (sleeve to ground, inner conductor to the ring as shown in the drawing)
  8. Fine-tune the resonancy frequency by bending the ring with an antenna analyser or tune for the best reception of the station or relay you aim to.
  9. Have fun and do lots of QSO’s.

    ring antenna swr chart
    ring antenna swr chart
  10. Share my blog’s web address 🙂

How well does it play?

 

Without any tuning the analyzer did show good results already.

An SWR of 2:1 is totally accepable on UHF in my opinion.

I aimed for a resonance freqeny of 431 Mhz, while it turned out to be

433Mhz. Bending up the loop increases the r.freqency while lowering it

down to the metallic gound lowers the frequency as espected.

Note that a single mm of diffecrence in distance can make a whole Mhz.

As well as other small loop-type antennas, the bandwith is pretty narrow.

 

Tested… Although being resonant it is definitely not as efficient as my commercial diamond X-30 nor can it keep up with the most simple type

uhf Lambda/4 can antennas that I have created many times before.

It still works well for the urban area I live in, covers a radius of 20km without any problems and does reach out to every repeater my X-30

reaches out for, too. (the most far is 70km away). I did all test while using my cheap baofeng GT-3 and 5 W of rf power.

 

Final thoughts on improvements.. Thickening the radiator conductor will increase bandwidth while adding a low loss capacitor will make it more precisely tunable. Whether this antenna type is also suitable for shortwave operation only the future experiments will show.

 

You are welcome to also try to build one.

What about a 145Mhz or even 50Mhz band type? If you have successful rebuilds, trouble, ideas or suggestions please leve a comment or contact me directly.

 

vy 73, keep it awesome.

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