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WL100 diversity removal

Want a little more output power and receive sensitivity from your Compaq WL100? If yes, then read on...

Written by: G4RFR ( FRARS ) Tuesday, 2 April 2002

Click for full size imageThe Compaq WL100 is a fairly good card, based on the Intersil prism 2 reference design. Probably the best feature of this card is the advertised 100mW output power. (Although measurement of this proves it's a lower power)

The major problem with most PCMCIA cards that are to be incorporated into fixed link wireless networks is the antenna diversity switching. The original idea of this was to allow the card to switch between two antenna's of different orientations that are printed on the PCB. This allows the card to obtain optimum reception as the card moves around, picking the best antenna for the lowest bit error rate.

However, in a point to point link, we know which antenna will provide the maximum signal, as we have aligned it to point to it's link partner antenna. According to the Intersil technical FAQ site, it is possible to override the diversity function in software by setting bits.

Since I dont profess to being Mr Software, I prefer to adjust the hardware and RF stages to suit my requirements. I leave software to the likes of Steve and Neil who've built this website.

Looking at the picture, you will see the coaxial cable that has been added to the card. The diversity switch U17 has been removed and the inner of the coax connected to C3005 which is a very small surface mount capacitor. Looking at the design on the RF input stages, you can see that compaq have adhered to Intersil's recommendation for the "improved antenna matching section". The other components that support the diversity switch can be removed also. These are two surface mount resistors that fed the actual switch and two capacitors that were DC isolators for the on board antenna's.

The coaxial cable has a line SMA socket fitted for connection to the external antenna.

Another possible mod, involving the diversity switch would be to add two external antenna connections. When used with two directional antenna's as a node, the diversity switch will connect the correct antenna according to the link in use. A high gain omni could be connected to one port, and a dish for link backbone to the other port for example.

Obviously, dont undertake this modification if you have poor eyesite or dont have a lot of electronics experience, as I wouldnt want you to disable your wireless lan card!!!

Links:

  • More FRARS Wireless LAN articles [Click here]

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