Building an IOio satellite antenna

I've had this post on my to-do list for a couple of weeks, but I needed to wrap up the build and take some pictures before I could write a complete entry. 

It wasn't until after I got my license that I became fully aware of the fact that there are orbiting ham radio satellites which can be used to make QSOs with little more than a 5 watt radio and a directional antenna. Step one for me was to buy an HT, which I did as a Christmas present to myself back in December. I had hoped I would be able to make the occasional QSO using a Yaesu VX-7R and a Diamond SRH320A whip antenna, but after many fruitless attempts I concluded that I needed better "ears." I had been planning to buy an Arrow satellite antenna, but they're about $170 and I like home-brewing. Enter the IOio.

The IOio was designed by EA4CYQ as a home-brew portable satellite antenna that was easier to transport than the Arrow but had similar receive and transmit gain. He wanted something that was "two-dimensional" instead of "three-dimensional" (the Arrow is a pair of yagis at 90 degrees to each other), lightweight, and somewhat collapsible. You can read his original build instructions and such here (PDF format). They include a good diagram of how the antenna goes together. The IOio seemed like a simple place to start my quest for a better satellite antenna so, after familiarizing myself with the design I got together with my friend Nick, N1UBZ, and set to work.

My first stop was Nick's garage. His landlord is a charming old man who lives next door, and Nick's garage is filled with the detritus of a lifetime of handywork. Hose reel made out of a Mustang alloy rim? Check. Massive air compressor? Check. Overhead chain hoist? Check. It also has a wide variety of scrap metal, wood, and plastic. We found a nice piece of 1" PVC with thin walls, 51" long so more than enough for the antenna and some excess to hold onto. Then we headed off to Discount Builders' Supply. It's bigger than a hardware store, but smaller than a Home Depot or Lowes, so it has a big selection of stuff without you needing a map to find your way around.

The first thing we needed was something to use for the elements. EA4CYQ's instructions are a little light on details about what materials he used. For the elements he just mentions "steely wire." For more detail I turned to 2E0HTS, a ham from Northern England who likes to work the ham sats, builds his own antennas, blogs, and posts YouTube videos. He's made a few IOios, and his instructions here were enlightening, as he mentions using TIG welding wire. We headed for the welding section, and after a little poking around we found 1/8" diameter copper-coated steel welding rods, in pre-cut 36" lengths. Perfect! The steel will bend, but hold its shape better than solid copper, yet the copper outside will be a snap to solder to! We bought six rods at $0.69 each. A packet of 4" cable ties and a roll of 3/32" rosin core 40/60 plumbing solder rounded out our purchases.

Back at the ranch we got to work. The first step was making the 435 MHz driven and reflected elements. These were easy enough, since both are shorter than 36", so they could be made out of one rod each. The driven element is a rectangle, 4.25" by 9.37". The reflected element is just a straight rod, 13.25" long. 

Drill your first 1/8" diameter hole near one end of the PVC pipe and make sure it goes straight through! You don't want crooked elements later. Then cut your driven element to length, 27.25", and pass it through the first hole. Measure 8.95" from each end and make a 90 degree bend there. Now measure 4.25" down from each bend and make another 90 degree bend there. You should now have a nice straight rectangle; bend the ends out 90 degrees, parallel with the short sides, so that there is about a 1" gap between them. Drill a second hole in the PVC pipe for the ends of the element to fit into. Try to make it more of a slot than a hole, 1/8" by 1/2". Slide two of the shaft collars over each end of the element, and then wiggle it around until you hook each end into the slot you've drilled. You can lightly tighten the shaft collars for now, we'll set them up properly later.

Drill another 1/8" hole in the PVC, 2" below where the straight part of the driven element sits in its slot. Again, make sure it's straight and that it lines up with the others. Insert your reflected element into that, slide a shaft collar over each end and lightly tighten to hold it in place. Congratulations, you have a 435 MHz antenna!

The 145 MHz elements are harder to make, as both are longer than 36", and so will need to be made from two pieces of rod soldered together. The reflected element needs to be 39.5" long. Rather than taking one 36" rod and adding 3.5" to one side, we took two and cut 19.75" off of each, so the joint would be in the center. At first we tried just soldering the rods end to end, in a butt-joint, but it wasn't strong enough. Nick rummaged around in the garage and came up with a piece of scrap sheet copper. He cut a little 3/4" square out of it with tin snips, rolled it into a tube, and used it to sleeve the ends of each rod. Don't make the tube wider, because we want it to sit entirely inside the PVC. We clamped one rod, and I held the other steady, while Nick applied a torch and solder. On his first attempt he applied too much heat and ended up burning off the copper coating, so it wouldn't take solder anymore. We flipped the rod around and went a little easier on it for the second try, and it worked perfectly. 

The 145 MHz driven element is the hardest of the four to make. It's a rectangle 27.75" by 12.75", so that's 81" long. Since it's going to be open at one end anyway, just like the 435 MHz driven element was, we cheated a little bit. First, drill a 1/8" hole 4" down from the 435 reflected element. Again, try to keep it aligned with the holes you've already drilled so everything comes out straight at the end. Take one 36" rod and pass it through. Make two 90 degree bends in it at 4.12" (4 and 1/8") from the ends. Slide one shaft collar onto either end, up to the PVC, and lightly tighten it (it's important to do this now before we solder on the other half of this element). Take two more 36" rods and cut 22.5" off each. Make a 90 degree bend in each of those at 8.63" (8 and 5/8") from one end. Now solder each short side onto one end of the piece you installed earlier, making one large rectangle! As with the 435 MHz driven element, bend out the open ends of this rectangle 90 degrees, and then drill slots in the PVC for them to clip into.

To install the 145 MHz reflected element, drill another hole 6" down from the slot that the driven element snaps into. This hole will need to be a little larger than 1/8", to accommodate the solder joint, but try to keep it as small as possible to minimize wiggling of the element when you are pointing the antenna. Attach two more shaft collars and you're done with the construction!

All that's left to do now is solder a piece of coax to each driven element and connect it to a diplexer, or to your dual-band, dual-antenna rig if you have one (or, if there is such a thing). I only had one piece of scrap RG-6 coax handy (left behind by a cable TV installer), so we decided to solder that to the 435 MHz element temporarily, so we could test it and I could use it t
o practice listening to the sats. The braid of this coax turned out to be aluminum, so it wouldn't solder to the copper of the elements. Nick bodged it together by tying it on with a piece of desoldering braid, and then soldering the braid to the element. The center pin soldered up with no issues. I will say that Nick has a Metcal soldering station. I suspect that my cheap-o Weller would not have been able to cope with the amount of heatsink that the antenna elements provide.

Nick has an antenna analyzer, so we used it to check out the 435 MHz antenna. It's resonant at 443 MHz, and the VSWR at 435 is 1.58. That's pretty good for DIY, I'd say! I don't know if it will get any better when I switch to 50 ohm coax or not. You can see the output graph here.

The last step is to tighten up the shaft collars. In order for them to get a solid hold on the PVC, I used a pair of vise grips to lightly squeeze the pipe while I tightened the collars. Then when I released the grips, the pipe pressed against the collars snugly for a good grip. 

That's it! My main take-aways from the build experience were to be precise when drilling holes in the boom, so the elements don't wiggle around; have the shaft collars on hand before you start so you can put them on before you solder anything; and bend the rectangular elements after you insert the rod into the first mounting hole (so you can keep that hole small). If you look at the photos of the finished antenna you'll see that I used some zip ties to anchor the front end of the 145 MHz driven element to the 435 reflected element, because I couldn't fit the shaft collars on after we had soldered it up.

So far I have only used the antenna as a receiver, but it works really well for that. I've been able to listen to several passes of AO-51 just standing in my living room and pointing it towards my large east-facing windows. I haven't had a chance to take it outside for a full horizon-to-horizon test, but hopefully I will soon.

Many thanks to Nick for all his help with the construction, and to Rob, AK6L, for the coax. You can see some photos of the build process and completed product here. My next project will be to build a diplexer, so I can use the TX antenna and start making some QSOs.

Lengths of elements ("front to back"):

435 MHz driven element: 9.37" (9 and 3/8") by 4.25"
2" space
Reflected element: 13.25"
4" space
145 MHz driven element: 27.75" by 12.75"
6" space
Reflected element: 39.5"

Materials list:

175" of welding wire (McMaster Carr - 1 lb package)
36" or more of 1", thin-walled PVC pipe
A small amount of scrap copper sheet
4" cable/zip ties
12 set screw shaft collars with a 3/16" inner diameter (McMaster Carr)
3/32" rosin core 40/60 plumbing solder
Two pieces of coax, length and type (50 ohm preferred) of your choosing
Strong wire cutters or tin snips
Propane torch
Power drill and bits
Digital calipers (very helpful but not crucial)

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2 Responses to Building an IOio satellite antenna

  1. Rob AK6L says:

    Great post, excellent detail! Your SWR at 435 should drop to very nearly 1:1 when you switch to 50 ohm coax; the 75 ohm to 50 ohm mismatch is 1.5:1 (though even this is not a big deal). I’m excited to see your results after you build and connect the diplexer!

  2. Mark says:

    I was just going to say what Rob said: if you use 75 ohm coax on an antenna which is matched for 50 ohms, you’ll get a 1.5:1 SWR mismatch (still pretty good, and the 75 ohm coax is probably less lossy than cheap 50 ohm stuff anyway). If your friend’s antenna analyzer could output the resistance/reactance measurements separately, you could probably see this: the low dip in swr is probably where reactance drops to zero, and you’d expect to see the resistance right around 50 ohms.

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