CNet CNWLC-811-3V Wireless Card External Antenna Mod

This piece of surgery was inspired by a page describing an SMC-2632 802.11 Transceiver Modification to add an SMA connector for external antennas. The pictured SMC-2632 strongly resembled a CNet CNWLC-811-3V wireless adapter in the author's possession, suggesting that the CNet might also contain concealed PCB pads for an external antenna jack. A coalition of the willing was formed to expose the secrets of this card.

The impressive array of tools recommended for the SMC mod were deemed unneccessary, and a lone medical scalpel was used instead. A sticky cosmetic panel was peeled up from the top of the card and a 1/2" square portion of plastic was excised from the card end, revealing paydirt: a PCB layout identical to the SMC.

In retrospect this guesswork could have been eliminated by performing a search for the card's FCC ID ( LLM002WL11000-1) on the FCC's Equipment Authorization System web site. FCC authorization applications typically include schematics, internal and external photos, user manuals and test reports detailing real-world behaviour of the product. (If you have a cellphone, you are advised to look up its authorization application to gauge your degree of EM radiation exposure.) In this case, investigation revealed that both the SMC and CNet are retail branded versions of Eumitcom Technologies' WL11000-1 implementation of Intersil's Prism2 chipset reference design. In fact, many different companies have released this card under their own name; a Google search on the WL11000-1 turned up references to the popular Netgear MA401, as well as Lincomatic's excellent page on modifying the identical US Robotics 2410. His pictures are much nicer than ours.

Speaking of pictures, here they are:

The PCB incorporates two patch antennae, with a discriminator chip which selects between them according to received signal strength. The reference design for the card includes a circuit for using an external antenna jack in place of one of the patches. Although not used by the manufacturer, this capability also exists in the PCB layout. To exploit it, a surface-mount inductor which connects one side of the discriminator chip to its associated antenna must be removed. An SMA jack is soldered to the board in the holes provided. Two tiny 150pF 0402 (1mm by .5mm) capacitors are added to unpopulated pads in the vicinity of the jack, coupling it to the chip.

There are three pads on the PCB to allow for the coupling cap or inductor from the discriminator to be oriented either toward the patch antenna or toward the jack. I wanted to retain the inductor onboard in case the mod was not satisfactory, so I moved it out of the way and resoldered it to the patch antenna pad. A reverse-polarity SMA jack from an old Proxim RangeLan card was used for compatibility with the wide range of inexpensive external antennas which use RP-SMA. For general use I attach a rubber-ducky antenna which is mechanically supported by the jack, replacing it with cheap Airlink101 ASB-8DA 8dBi directional or ASB-7MA 7dBi omnidirectional antennas when the need arises.

As I understand it, the signal strength measurement provided by the Linux Prism2 drivers is generally not very accurate due to variation in card manufacturer's implementations. Indeed, tests with the Linux wlan-ng and hostap drivers don't produce consistent numeric results, but do show a marked comparative improvement in signal strength with an external antenna attached.

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