Tinfoil hat (for EVDO)

July 28th, 2010

The things you’ll do when you’re sitting around the house…

The other day I built a parabolic reflector out of cardboard and some foil tape I had lying about. I was researching various homemade antenna designs I want to tinker with and stumbled on one that I actually had all the parts for on hand. As we are so close to the edge of EVDO reception here that moving down the hill a few feet would kill the signal, it seemed like it would be worth a shot. After all, it cost maybe fifty cents for the foil tape I used and the cardboard was free.

Parabolic EVDO Antenna.

Now, this is hardly a good mobile solution as it’s fairly directional, but after spending twenty minutes or so on the roof pointing the reflector and testing bandwidth, I got pretty good results. The SNR increase doesn’t even register on the cradlepoint’s web interface, which is fairly lackluster, so I had to result to ping flooding our upstream router to detect a better signal. No, I didn’t DoS it, I kept the packet count to 100 at a time while aligning and 1000 packets for bandwidth testing.

I didn’t record all the numbers, but to give you an idea of the improvement: without the reflector, we were seeing 10-30% packet loss and average roundtrip times that ranged from 5 seconds to 9.5 seconds. Even at that, the connection was usable. Once the reflector was aligned, packet loss dropped to 0-1% and average roundtrip times stayed about 2.5 seconds. This equates to a 100-300% increase in bandwidth plus the bandwidth recovered from dropped packets.

The connection is hardly blazing fast, but it’s quite a bit more usable than previously. For our normal usage patterns, it’s actually quite acceptable. Bear in mind that our average roundtrip times are similar to 380ms. The previously stated times are for icmp packets being sent out as fast as possible and saturating the connection.

With that sort of improvement, I’m much more determined to build a waveguide antenna for times when we’re having trouble hitting a tower. Bonus points if I can fit both the wifi and 3g spectrums into the same antenna and use it for a wifi repeater as well.