[plug] OT: Point to multipoint wireless

[Kai Jones]

> -----Original Message-----
> From: plug-bounces at plug.linux.org.au
> [mailto:plug-bounces at plug.linux.org.au]On Behalf Of Onno Benschop
> Sent: Monday, 15 March 2004 11:48 AM
> To: PLUG
> Subject: RE: [plug] OT: Point to multipoint wireless

[..]

> > QSL
>
> Huh?

Sorry, that's amateur radio speak for "Acknowledging receipt (of
information)", ie no worries, all understood.

[..]

> > > 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.

Fair enough, in the world of experimenting with wireless I don't really care
what method I use so long as it isn't dodgy and it works well :)

> > 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.

Yep, same-polarisation is the best way to go, that's why I'm going to use
vertically polarised antenna's, and I think you missed the detail in one of
my previous email that says FDC <-> BRAC is roughly 150 metres, and once
Depot's admin is moved they will be less than 300 metres fom Depot <-> BRAC.
:)

If I was going to try and get BRAC and depot to talk from their current
locations I'd look at putting up a mast on BRAC's roof and two horizontally
polarized high gain antenna's on top of that, possibly log periodic yagi's
if needed - but I'm not going to try that because I'm thinking there are too
many obstacles in the way.

> 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.

Exactly what I thought would be inside them, I have been considering
building the yagi antenna, but even on my wage, getting parts and time taken
to properley assemble the antenna wouldn't be worth it, easer to buy the
thing and put it in the air. They say it's weatherproof and corrosion
resistant but that would be the case with nearly anything you put in a
section of sealed conduit !

D-Link's page says there's 1.5' of cable that comes with the antenna, enough
to mount the AP on the mast and have a bit of slack.
The http://www.dlink.com/products/?pid=289 is what I'm looking at to put on
BRAC's roof, they say it has a cable length of 3 metres, so that's ok but
I'll still try to get the AP as close to the feedpoint as possible, might
wrap the antenna cable into a 5 turn coil about 15" from the feedback
because I've heard that supresses noise if it's done close enough to the
feedpoint.

I'll be running Ethernet in as many places as possible to avoid loss before
the signal reaches the antenna.

> (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

Yep, QSL.
I have some SWR and field strength equipment at home which I can borrow if I
have concerns about signals.