[plug] OT: Point to multipoint wireless

[Onno Benschop]

On Mon, 2004-03-15 at 14:12, Kai Jones wrote:
> > -----Original Message-----
> > From: plug-bounces at plug.linux.org.au
> > [mailto:plug-bounces at plug.linux.org.au]On Behalf Of Onno Benschop
> > Sent: Friday, 12 March 2004 12:58 PM
> > To: PLUG
> > Subject: Re: [plug] OT: Point to multipoint wireless
> [..]
> >
> > My point is this:
> >
> > Heat is not your problem. I have set this up in Kununurra,
> > Darwin and in
> > the middle of Australia with absolutely no problems.
> >
> > Water is your problem.
> >
> > So, my advice, get a waterproof box, bolt the thing inside and forget
> > about it.
> >
> > Hint: Make sure you can remove the lid so you can press the
> > reset button
> > if you stuff up the installing of new firmware or configure it to use
> > DHCP to get an IP address you cannot get to... (or write down the MAC
> > address before you seal the box)
> 
> QSL

Huh?


> I meant I'll factor in two for each location, we'll have a total of three
> AP's once the depot moves in so maybe I'll ask for two spares, but I'll
> definately put in for spare and give reasons.

More than one spare seems a little overkill, but I suppose it depends on
how mission-critical it really is.


> > But then again, "What do I know?", I just build it and use it, so you
> > can ignore anything I said.
> 
> "so you can ignore anything I said"
> I don't know why you said that, your advice and experience is very usefull
> and I'll keep it in mind.

First, thanks for the complement.

I said that you could ignore me in the way of a disclaimer, because I've
found that some take offence at my sometimes strong wording. I've found
that a lot of art is associated with 802.11 (if you are not a radio
technician with lots of testing hardware), so many differing opinions
exist that all attempt to address the issues. I didn't want to invite a
flame-war that went along the lines of: "But I've done it this way and
you are wrong and besides you're talking rubbish." - so instead I put in
the disclaimer.


> There probably won't be any walls between the two antenna's.
> The yagi antenna I'm looking at is http://www.dlink.com/products/?pid=56,
> it's got 18dBi, which probably measures to around 10 dBd, it's vertically
> polarised which is good 'cause then it'll talk to BRAC's (Rec centre)
> omnidirectional antenna better and they rate it at max 200 k/hr winds, which
> I think is Category 3 cyclone wind speeds.

Ok, I'm not sure that what you write here is correct, and it might well
be that your radio experience helps you here more, but lets just expand
a little on this.

I'm understanding that you want to put a directional antenna in one
location and an omni in the other. My understanding of how 802.11 works
is that both antenna fields need to overlap because you need to have a
two-way path. So unless the omni has a range of 1300 m, I think you may
have a problem.

Also, I own two of the antennas in the link you provide and I couldn't
help myself and had to open up the water-pipe to see what was inside.
Never (IMHO) a less-sophisticated sight was seen. The antenna basically
looks like a TV antenna. It has one stalk along the length of the
antenna with side stalks on two sides - making one plane of antenna if
you like. The polarisation is in the alignment of the antenna and I
didn't see anything that convinced me that it was put inside the
water-pipe with anything but "She'll be right mate." The sticker
indicating the polarisation seemed just tacked on.

(Which is all to say that it's a lot of money for a piece of wire and I
suspect if you really want 10Km range out of them - which is why I
bought them - you'll need to seriously tune them.)

A few things you don't say you've considered are:
      * Lightning protection - some antenna cable bits exist for this
        and they will reduce the sensitivity of the antenna.
      * The longer the cable between the AP and the antenna, the poorer
        the result. I decided to bolt the AP to the antenna - use the
        standard tiny antenna cable and run Ethernet up the pole.
      * If you run Ethernet up the pole, you'll also need to run power
        up the pole.
      * If you buy an antenna it often does not come with a long antenna
        lead, so you'll need to factor that in - that is if you don't
        put the AP in the pole.

One issue I have with the 900AP+ is that there is no signal strength
indication in the AP, so my best attempt is to do a flood-ping across
the link and get the packet loss as low as possible.

Hope this helps,

Onno Benschop 

Connected via Optus B3 at S41°18'23" - E146°49'07" (Holwell, Tas)
-- 
()/)/)()        ..ASCII for Onno.. 
|>>?            ..EBCDIC for Onno.. 
--- -. -. ---   ..Morse for Onno.. 

Proudly supported by Skipper Trucks, Highway1, Concept AV, Sony Central, Dalcon
ITmaze - ABN: 56 178 057 063 - ph: 04 1219 8888 - onno at itmaze dot com dot au