Sunday, March 16, 2014

Quick, easy, and cheap 1090MHz ADS-B antenna

Having recently discovered the joys of RTL-SDR dongles, I decided that I wanted a dedicated ADS-B receiver using one.  The details of setting up the dongle and configuring the software are beyond the scope of this post.  If you're interested I'll be happy to make a post about it sometime, though.

I'm sure that if you've read any of the other posts that I've made on this blog, you have come to the realization that I am an unrepentant cheapskate.  Since I spent a whopping $12 on the USB dongle, I sure didn't want to spend very much on the antenna.  After finding suitable plans online (the math on single-wire collinear antennas is beyond me), I headed off to Home Depot to see what we can find in the way of suitable materials.  Here is what I came up with:

12ft of 10ga solid copper wire: $8
Two 1.25in x 24in PVC pipe: $5
Two 1.25in PVC caps: $2
One 1.25in PVC coupler: $1

I already had an SO-239 panel mount connector in the parts bin, so that sums up my cost on this.  $16 total.  Can't complain about that, I guess.

This pile of parts will eventually become the antenna:

If you looked at the antenna plans that I found, you'll see that some coils are needed in the antenna.  The outside of a PL-259 is almost the proper dimensions.

To get it up to where it needs to be I added a couple turns of masking tape to the outside of it.

After a bit of practice (as you can see in the background), I had two lengths of wire with suitable, although not perfect, coils.

Here is where I deviated from the flight plan on this.  It turns out that Home Depot doesn't stock flat pipe caps, or even PVC pipe flanges, so having a flat sheet of metal as the groundplane was right out.  Instead, I decided to build a vertical collinear dipole!

I had a dilemma on this.  If I used wire thin enough to fit into the SO-239 I was worried that it would bend when going into the radome.  But a larger wire wouldn't fit properly, so I decided to take a small piece of 1/4in copper tubing and use it as an adapter.  I solder the solid wire into it first, then created a solder filled cup in the other end, into which I set the post from the SO-239.  It works well, just be care to not get the connector too hot, otherwise the teflon in the connector will melt.  Also, be sure not to torque the post too much, it breaks easily.  This is why I decided to use a radome of PVC, to protect that fragile part.

The one step that I didn't take pictures of was putting the antenna into the PVC radome.  I used some foam wafers cut from old packing material as a dielectric standoff to keep the wire centered in the pipe.  I also built a 2m groundplane that used a similar technique, I will post pics of it soon so that you can get the general idea.

And here is the end result!  It seems to work fine business!  Within a couple of seconds of plugging it in I was up and receiving ADS-B signals.  And this is with the antenna at a measly ten feet off the ground!

Anyhow, I hope that you have enjoyed the post and wish you the best in your antenna making adventures!


Richard, KK4JDO

1 comment:

  1. 1090 Mhz is pretty neat for making antennas.. I found a home brew that was really small and a great performer.. Info at this link..

    I made an antenna tester, so I could tune it up..
    It allows me to get the relative reflected power... (Return loss).. Makes it easier to tune up things.