|Ralink USB wifi adapter external antenna modification
||[Jul. 9th, 2006|09:59 pm]
I recently bought a Ralink-based 802.11g adapter on eBay to use with the Aircrack-ng suite on a linux platform and decided to add an antenna connector to enhance its usefulness. This modification was partly inspired by the success I've had using a similarly altered Microsoft MS510 adapter and also by Tobias Hain's hack of an Asus WL-167g. |
My USB device is a Scientific Atlanta/WebStar DPW939, which a rebadged
WL-167g so I won't cover the disassembly stage - this was nicely
summarized in the link above. The connector I used was a CONREVSMA03
made by Linx Technologies and purchased through DigiKey. This connector
is a card-edge design, so it protrudes from the end of the USB stick
along the same axis. This is the connector:
Linx makes this connector for two different thicknesses of boards, .031" and .062". This adapter uses a board that measures around .035 so I went for the larger size. As it turns out, the .062 connector measures more like .070, so I believe the smaller size would have been a better fit. As a result, I needed to shim the gap to hold the connector's legs flat against the opposite side while I soldered the center pin. I used the thin end of a plastic tiewrap to snug things up.
The front side of the connector with the center pin soldered. Note the bare pad above the connector's upper leg, this is the ground pad from the original antenna which I removed.
Although it looks a bit blobby, I bridged the gap between the leg and the pad with a brass pin I salvaged from a jumper header of an old motherboard.
I gently clamped the case in a drill press vise, and drilled the end with a 1/4" bit. I should have clamped the case closer to the plastic end to prevent the drill bit from popping the two halves apart, but it still worked ok.
The back of the board has no bare copper to solder to, so I potted the legs with some epoxy. You can see that I snipped a piece of the tiewrap to fill the gap between board & leg.
The finished product. Although I'm showing it with a rubber duck antenna, I will mostly use a short pigtail to connect this to a much larger antenna =) In practice, I've found the Ralink USB adapters (I also use a similarly modded linksys WUSBGv4) to be markedly less sensitive than Prism or Zydas-based adapters when running in rfmon mode. Hooking them up to a big honking dish antenna certainly improves the situation.