UHF Helical v4 - Instructions and source

Hello all,

Please find the instructions for the new UHF Helical v4 here:

You can check out the source files here: https://github.com/satnogs/satnogs-antennas/tree/master/Helical/UHF-434-8

Please provide any feedback here. Thanks!


This is fantastic, looking forward to building it. I’m very happy to see the larger reflector. And it’s great to see the solid triangle pieces, this should help control helix diameter.

Some questions:

  • First a silly question: what are you using to cut the shapes out of the plexiglass/polycarbonate sheet?
  • This design calls for brass wire. Is brass strictly required?
  • The dozuki could mention the very helpful measurements on the spreadsheet in the github repo! This was sorely missing on the v3 design, and I found myself struggling with a .dwg viewer to guess the offset (my viewer didn’t have a measuring tool!) of the mesh from the end of the boom. Having this positioning out by +/-10mm affected VSWR response quite drastically. I was lucky to have an antenna analyzer, most others probably don’t. But the measurements are already in the spreadsheet, so you should mention that :slight_smile:
  • Several steps say to “check impedance with a multimeter”. Multimeters generally only measure DC resistance, so should we really just say “resistance between the helix and the reflector”? I’ve found many electronics hobbyists asking about our SatNOGS build at MakeHackVoid, who will look at me funny if I say “impedance” instead of “resistance” :slight_smile: It would be useful to be more direct “check with a multimeter that there is no short between reflector & helix”.

Cheers, and thanks for all the hard work, it looks great!

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On our versions we waterjet them. You may also use a CNC or a laser cutter.

Brass wire is what we’ve tested. It is possible that aluminum wire would do the job just fine. Although it might be almost impossible to weld it.

Nice catch! Just added a note with bold text on top of the guide.


Thanks for your feedback! This is really helpful :slight_smile:

Thanks @pierros, we are hoping for our glowforge laser cutter to be delivered later in the year, seems like a great project to try it out on. Going forward, is it your intention to retire the v3 design or will it perhaps still be maintained/supported for those of us without any CNC gear?

Brass wire is what we’ve tested. It is possible that aluminum wire would do the job just fine. Although it might be almost impossible to weld it.

Can I assume the diameter is not terribly critical? The reason I ask: we have lots of 2mm galvanized steel wire left over that the v3 design calls for :slight_smile:

No retiring of any design will be done :slight_smile: We are putting everything public and open source for people to contribute and have access to, so no worries!

The diameter is not “terribly” critical, that said you would be best by testing the end result with a VNA (if you have access to one).

A newbie question:
There are a few DIY antenna analysers , using Arduino and DDS like AD8590.They have a
Are they suitable for SatNOGS helical antenna or only for HAM radio antennas ?

Hi everyone.
Here is a NEC2 card file for the 2m band 434 MHz helix. It is good for a tracking receive antenna and has about 12 dB gain.

At this size, a crossed Yagi would be rather easier to build though. A helix is more suitable for the 70 cm band.

CM Helix, SatNOGS, v4
CM Frequency: 434 MHz
CM Wavelength: 691 mm
CM c=299792458 m/s
CM Radius = 110 mm
CM Turns: 8
CM Circumference to wavelength ratio: 1
CM Reflector perimeter to wavelength ratio: 0.8 = 553 mm
CM Winding diameter: 220mm
CM Winding circumference: 691mm
CM Winding spacing: 172 mm
CM WInding length: 5696 mm
CM Reflector perimeter: 553mm
CM Total length = 172 mm x 8 t = 1376 mm
CM Reflector plane 1 mm below zero to avoid a short with start of helix
CM Feedpoint(1) - Z: (111.340 - i 1152.400) I: (0.0001 + i 0.0009) VSWR(Zo=50 Ω): 99.0:1
CM Antenna is in free space.
CM Directivity: 11.08 dB
CM Max gain: 12.51 dBi (azimuth 0 deg., elevation 90 deg.)
GH 1 500 0.172 1.376 0.110 0.110 0.110 0.110 0.003
SM 10 10 0.277 -0.277 -0.001 0.277 0.277 -0.001
SC 0 0 -0.277 0.277 -0.001
EX 0 1 1 0 1 0 0 0 0 0 0
FR 0 1 0 0 434 0
RP 0 90 90 0 0 0 1 4 0 0 0