Category Archives: em-406

Update on wardriving/walking/cycling setup

The stackup that I did inside the enclosure was fairly crude. The GPS receiver and its attached antenna are at the “top” of the stack, and stuck to the inside uppper surface of the enclosure using double-sticky foam tape. Immediately below that, the dual-band Wi-Fi board is component-side down. I’d removed both the SMA-RP female and the USB male board connectors to reduce height and length. The bottom of the stack is the USB hub, again with USB female sockets removed and component side down as there’s two electrolytic caps that stick up 8 mm or so.

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I’ve used double-sticky foam tape for things like this over the years, and as long as it doesn’t absorb moisture, it’s quite RF-transparent and the antenna has no issues.

The Wi-Fi board has a ground-plane on top and bottom, but I wanted to reduce to a minimum any local fields from the components, so the board goes in component-side down to isolate it (maybe a bit) from the GPS antenna.

The GPS receiver itself is completely encased in a shield, and is slightly larger than the antenna, so there may be some added attenuation of spurious emissions from the Wi-Fi getting into the GPS.

The USB hub, at the very “bottom”, also has a top/bottom ground plane.

The Wi-Fi sniffing performance is as good as my permanent mobile setup, and the GPS gets excellent PDOP (<2.0) when there’s a decent field of view of the sky.

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The apps used to grab the GPS data is 4river’s NMEA Monitor, a fine little program.

Highly Portable Wardriving, Warcycling, and Warwalking Setup Update

Before I left on a trip this past week, I was able to shoehorn all the components (GPS receiver w/integrated antenna, dual-band Wi-Fi module with external antenna input, 4-port USB hub, TTL to serial to USB adapters) into a single plastic case. It’s not yet weatherproof, but at least it’s splash- and rain-resistant.

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The original cable on the USB hub was only a meter, so I grabbed a 2 m cable from the box, whacked off the end, and replaced the shorter cable.

I used double-sticky foam squares to create an electronics sandwich, with the GPS antenna at the “top” of the stack, the Wi-Fi below, and the USB hub at the bottom. The cable passes through a silicone-sealed hole in the case, and I removed the SMA-RP female from the Wi-Fi dongle and replaced it with a short RG178 cable and bulkhead SMA-RP connector that pokes through the top of the case.

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As one can see, the box is a cheap one from Radio Shack or similar, it’s some kind of ABS. The box’s lid, which would usually be on the top, is now the bottom of the assembly. I silicone-glued 3 NdFeB rectangular magnets to the inside of the lid, and put 4 rubber-bumper feet to reduce any potential surface marring. Next, I took the thing out for a drive on a local freeway to see if it’d blow off. It did. I adjusted things a bit by getting rid of the rubber bumper feet, and replacing them with electrical tape on the outside of the lid for more of an anti-skid, compliant surface than the bare plastic alone. The next drive, and subsequent ones this week, proved that the widget is now fairly stable even at “high” highway speeds. I thought about painting it white to reduce heat absorption, but that would make it have higher visibility and I’d prefer to stay low profile.

In taking it for a drive or two around the neighborhood, it matches my mobile setup almost exactly in reception, and takes all of 30 seconds to deploy when getting a rental car.

I’m wondering if I can somehow add a temperature sensor inside and read it via the USB. But that’s not so important.