djb Engineering Notebook
[Cards Tested] [Models] [Documentation]

Conexant (formerly Harris/Intersil) PRISM II/2.5/3


The PRISM I chip set was not 802.11b and was limited to 2mb.

PRISM FVO (Frequently Voiced Opinions)

O. PRISM 3 cards are not as good as PRISM II/2.5 cards.
R. PRISM 3 cards have fewer ICs and use a direct digital up/down-converting software defined radio (zero IF). PRISM II/2.5 cards use a digital up/down-converting superheterodyne software defined radio with a specified intermediate frequency (IF) stage. A superheterodyne radio is often superior, however in practice there is more difference in performance between different sets of cards than there is between PRISM II/2.5 and 3 chip sets.

O. PRISM cards from vendor X receive better. See table at some website or other ....
R. The difference in performance of PRISM cards among vendors can be just the difference in antenna structures of the cards. In practice there is little or no difference. A significant drop in performance from one card to the next most often means that the card is bad.

O. Vendor X access points/routers only work with vendor X cards. PRISM cards won't work with cards/access points/routers that use vendor R chip sets.
R. So long as all WLAN components meet 802.11b standards there will be no problems with interoperability. Some cards/drivers do not support all of the various encryption/privacy (WPA, WPA2) methods. Besides, as shown below, vendors may in fact rebadge hardware made by several different suppliers as the SAME MODEL!

O. I want a 100mW, 200mW, or 300mW card!
R. No you don't! Cards with higher output were originally intended for OEM use in routers or other networking equipment and may not work in typical PC Laptop Computers. In fact, the FCC requires that these cards MUST NOT work in Laptops. 802.11b is supposed to be a "Local" Area Network. Consider a directional gain antenna instead. Someone could easily snoop a 200mW signal from up to 3 miles away! BTW: that's milli-Watts == .001 watt. 200 Mega-Watts at 2.4 GHz would cook everything in it's path!
  • 370mW == 25.68dBm
  • 200mW == 23dBm
  • 100mW == 20dBm
  • 60mW == 18dBm == maximum output of PRISM PA (HFA3983/ISL3984)
  • 200mW - 60mW == 23dBm - 18dBm == 5dBm
  • Gain of simple directional 2.4GHz antenna => 5dB
  • Loss through window glass => -5dB to -15dB
  • Loss through trees/forest => -17dB/100 feet
  • Loss through 10 inches of moist concrete => -24dB "dry" concrete comes in a bag:)
  • Loss through air => -38dB/mile; -7.2dB/1000 feet
  • Signal through chain link fence == 0 Why ? The 1 to 1 1/2 inch links in a chain link fence form a reflector at 2.4 GHz.

O. 3.3 volt cards need a Cardbus slot. PC Card slots are 5 volts and will damage 3.3 volt cards.
R. No. Many 3.3 volt cards will work at either 3.3 or 5 volts.
From PCMCIA.org:
Why won't some cards fit into the slot on an older computer? The PC Card Standard includes definitions for the operation of PC Cards at two different voltages: 3.3 V and 5.0 V. A "key" was defined on the edge of the PC Card connector to prevent 3.3 V cards from inserting into slots that only operate at 5.0 V in order to prevent damage to the card. Some cards are able to operate at either voltage, and some slots are able to accept cards that operate at either voltage. If you have a card that will not fit into a slot, that means that the slot is providing 5.0 V and the card will only operate at 3.3 V. Do not attempt to remove the connector key, because if you do so and insert the card, the card will very likely be damaged beyond repair. The CardBus interface was defined as a 3.3 V-only interface, so they will not operate on a 5.0 V-only system.
Or.... Dual voltage cards are keyed to work in any PC Card slot. Dual voltage PC Card slots will accept cards keyed for either voltage.
5 Volt =>      3.3 Volt =>      Dual Volt =>

Tested PRISM II/2.5/3 WLAN Cards

Note on FCC ID and ODM/OEM info:
FCC ID listed has been verified via «FCC OET Database» . ODM/OEM info is often printed on the circuit board or included in the FCC data. ODM/OEM data can not be 100% verified. It would not be unusual to find more than one ODM/OEM per product.

NetBSD «wi(4)» driver

Eventually, all cards will be tested in all 3 platforms

  1. NetBSD/hpcmips - IBM Z50 Workpad
  2. NetBSD/alpha - Multia/UDB
  3. NetBSD/i386 - IBM Thinkpad 365XD and/or 560


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