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Wireless LAN


  • To: <ukha_d@xxxxxxx>
  • Subject: Wireless LAN
  • From: "Mark McCall" <mark@xxxxxxx>
  • Date: Mon, 18 Dec 2000 15:48:01 -0000
  • Delivered-to: rich@xxxxxxx
  • Delivered-to: mailing list ukha_d@xxxxxxx
  • Mailing-list: list ukha_d@xxxxxxx; contact ukha_d-owner@xxxxxxx
  • Reply-to: ukha_d@xxxxxxx

Interesting stuff on how Tim Morris is getting on with his wireless LAN....


  >I'm getting closer on the Wireless LANs. I know you're
  >interested, so just
  >to fill you in on where I've got to:
  >
  >The Compaq cards have a big advantage over and above the rest of
  >the world,
  >it that the PCI cards are a lot cheaper than all their competitors cards
  >with 128 bit encryption. (£125 vs £200).
  >
  >The problem they have (and all of them have), is that radio
  >waves really do
  >not like passing through the metal cabinet of the PC, so it restricts the
  >radio waves propogating from 360 to 180 degrees horizontally - vertical
  >propogation is around 75 degrees. The majors (Cisco, 3Com,
  >Lucent - which is
  >also sold under the Evansys brand at around the same price) all sell an
  >external antenna, but Compaq do not.
  >
  >To compound matters they use a proprietary connector on the board. I've
  >learned a lot about RF connectors in the past week, and it is an SMA
  >(subminature BNC but with a screw thread, instead of a bayonet) connector
  >with a left hand thread. I've fired emails all over the shop, and none of
  >the major connector suppliers make anything to mate with it. The industry
  >standard for Access Points (the best way to think of an Access Point is a
  >wireless hub, with an interface to wired networks) is Reverse
  >Polarity TNC -
  >BNC with a thread. The reverse polarity bit is designed for all microwave
  >antennae, to stop people interchanging HF and microwave antenna.
  >Certainly
  >Cisco use reverse polarity SMA on their boards.
  >
  >Cisco make two antennae that I'm looking into one at £122, and
  >one at £65.
  >Both have two elements to increase coverage. The more expensive
  >one has two
  >7 inch antennae which can be angled to suit, the cheaper has two fixed
  >antennae angled in a V at about 70 degrees. This gives pretty
  >good coverage.
  >There is a null zone in a 30 degree cone, above and below it,
  >but it should
  >offer coverage out to 300 feet in building at 11 Mbits. The only
  >drawback is
  >that it comes with a 1 foot cable - which is a total waste. I'm going to
  >order a couple tomorrow, plus the relevant bits to make some extension
  >cables (I'll wire the cables directly in to the antenna
  >providing the test
  >goes OK - joints tend to reduce the signal strength). I'll also order the
  >relevant (SMA Rev Pol) connector to go on to the PCI card,
  >desolder the one
  >that is on there and put it in a draw just in case of warranty (3 years)
  >claims.
  >
  >The costs are adding up, it can be cheaper if you go for 40 bit
  >encryption,
  >but I'm actually going between two buildings, so it is still cheaper than
  >getting someone to dig a 50-60 foot trench and lay cable in a
  >conduit - or
  >if you are that way inclined, less time consuming than doing it
  >yourself :)

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