Harley-Hardened Wire Helps High-Gain Antenna Hack

What does a Harley-Davidson motorcycle have to do with building antennas? Absolutely nothing, unless you happen to have one and need to work-harden copper wire to build a collinear antenna for LoRa.

We’ll explain. Never being one to settle, [Andreas Spiess] needed a better antenna for his LoRa experiments. Looking for high gain and an omnidirectional pattern, he bought a commercial colinear antenna, which is a wire with precisely spaced loops that acts like a stack of dipoles. Sadly, in a head-to-head test [Andreas] found that the commercial antenna was no better than lower gain antennas in terms of range, and so he decided to roll his own.

Copper wire is a great material for antennas since it can be easily formed without special tools and it solders like a champ. But the stuff you get at the home center is nowhere near stiff enough for a free-standing vertical whip. This is where the Harley came in: [Andreas] used his Hog to stretch out the 1.75-mm diameter (a little bigger than #14 AWG) copper wire. Not only did the work-hardening stiffen the wire, it reduced its diameter to the 1.4 mm needed for the antenna design. His vector network analyzer told him that ground-plane elements and a little fiddling with the loop diameter were needed to get the antenna to resonate at 868 MHz, but in the end it looks like the antenna is on track to deliver 5-dBi of gain.

Of course there are plenty of other ways to stretch out a wire — you could just stretch it out with hanging weights, or even with a go-kart motor-powered winch if you’re ambitious. But if you’ve got a bike like that, why not flaunt it?

46 thoughts on “Harley-Hardened Wire Helps High-Gain Antenna Hack

    1. 30 years or so ago someone tried a similar joke on me and sent me for a pack of guidelines.
      I went to the storage and returned with the message sorry all are finished but I ordered a 12 pack for 2500,- each.
      Never saw a manager run so fast to the mailbag to look for the order.

    2. Let’s not forget about elbow grease and light bulb repair kits.
      When my Dad was brand new in the US Navy, someone sent him to get a “bulkhead remover”. He was smart enough to know that they were messing with him, so he returned the favor and came back with a jackhammer.

    3. I worked at a pizza place and we’d send newbies to get the dough-repair kit to patch holes in the pizza skins (flatten-out pizza dough/crust.) At one time we had a small bag of flour in the walk-in cooler labeled “dough repair kit. Add water.”

    4. The best ‘sent to get story’ i heard is this:-
      An apprentice was sent to get a gross of 1/4 inch holes.
      Very soon he came back with a bag of 1/16 inch washers.
      When asked why he said ” the storekeper said he was fresh out of 1/4 inch but said that you could drill these out”

    1. I always thought that too, until I actually rode one. It was the most comfortable ride I ever had. They may not check all the boxes when it comes to performance and handling, but there’s something special about riding them that I just can’t put my finger on. Makes me wish I had borrowed my buddy’s bike more than once.

  1. It’s still a popular thing, especially where I work. I’m also a fan of what we did in the Navy: send people out to the bow to look for the mail buoy or giving them cardboard covered in aluminum foil to calibrate the radars. Probably a bit mean but damn it’s funny!

  2. For shorter lengths I find twisting copper wire with a drill works very well. It work hardens quite quickly but also comes out very straight, any bends in the wire with a radius more than a few cm will be twisted up until they cancel themselves out.

  3. A co-linear is made out of coax, this looks like a ground plane vertical. Stretching coax would mess it up, and it’s still limp. Also as the copper turns green it’s skin effect changes, most of these type antennae are stainless steel or aluminum. The length has to be a quarter or 5/8 high longer won’t do. A co-linear is able to be made longer for more gain, it turns inside out every half or quarter wavelength I forget which.

    Loops? Sounds like a Yagi with loops instead of flat dipoles, perhaps. Read up on this in the ARRL antenna handbook.

    Does some looking… Googling colinear comes up with an extra l (lima) and nothing in Wikipedia. Instead type “collinear antenna coax homebrew” the pictures will tell all. I now realize that collinear describes too many types. High gain happiness to all, but you will have to brush up on striping and prepping coax neatly and soldering too.

    1. So… Vorbild is a role model in this case, right? So… What would “geht anders” be here? Hero goes differently? What, “a role model does things differently”? I suppose that would make sense here. This is definitely a case of doing things differently.

    1. 1.7mm vs 1.4mm isn’t a big change in capture area compared to the wavelength, they are both tiny. The size reduction is probably important for capacitive loading and impedance matching.

  4. I remember a story from a friend who worked on the local Air-force Base, they had a new recruit that was insufferably hungry to do a good job, but was being a tad annoying, so they sent him out to find a 55-gal Drum of Prop-wash… After running around the entire base in a growing panic and being sent on one wild-goose-chase after another, he ended up crossing path’s with the base commander, when he asked HIM how the whole base could have so many aircraft and be entirely out of prop-wash, the base commander escorted him to the local supply depot where he was loaded with 2 barrels of “Simple Green” Concentrate… the Commander Followed the young Airman back to his supervisor and “suggested” that EVERY aircraft in the inventory shall be FULLY “Bucket Washed” by the end of the week or everyone involved would be on report……….

  5. Not an RF engineer, but I thought you could just use thicker wire and tweak the length a little to bring it to frequency. Seems easier (and stronger) than stretching the wire out?

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