At 1km, the path loss of 2.4GHz is almost 100dB. Combined with feed line
loss, that's going to be quite the challenge with omni antennas. Figuring
25dBm transmitters, a receiver sensitivity of -85dBm, 20dB of total feed
line loss and 8dBi of antenna gain at each end, the margin is less than
5dB. I don't think that's going to work reliably, and then there's the rain
factor along with outside interference.
Maybe a high gain antenna at the base that can automatically track the
vehicle? Is that available? More importantly, is that in the budget?
How about the option of using Cellular data and OpenVPN to secure your link?
This is the piclist after all; there's always the pessimistic view
supported with "facts", but then someone pulls it off. ;)
On Oct 11, 2017 3:36 AM, "Allen Mulvey" <***@amulvey.com> wrote:
> Have you given any thought to distributed access points? If
> there is networking available along the route you could use
> something like a Cisco Unified Wi-Fi system. Several years
> ago I bought some "end of life" radios and a few
> controllers. I distributed radios around my house and my
> church with a controller at each location. I could have run
> them off the same controller but I wanted them isolated. The
> user can move around the premises and his device will
> seamlessly switch to the strongest signal. My radios support
> both 2.4 and 5 mhz. I disabled the 5 mhz. side to save
> energy and the cost of additional antennas.
>
> Allen
>
> > -----Original Message-----
> > From: piclist-***@mit.edu [mailto:piclist-
> > ***@mit.edu] On Behalf Of Forrest Christian (List
> > Account)
> > Sent: Wednesday, October 11, 2017 12:38 AM
> > To: Microcontroller discussion list - Public.
> > Subject: Re: [BUY] Outdoor wifi antenna.
> >
> > At 1km the 80% fresnel clearance is 4.5m, so in a
> perfectly flat
> > and open
> > environment, you only need to be up 4.5m on both ends, or
> > higher on one end
> > or the other, so that the middle is above 4.5m. This is
> > assuming a
> > modulation where this truly matters. With OFDM, often one
> > can intrude into
> > the fresnel zone a bit more since the resulting multipath
> can
> > actually help
> > instead of hinder the data link in some cases (depending
> on
> > the obstruction
> > and the environment)
> >
> > I realize with one end being a bus, the OP may need to
> > elevate one end or
> > the other.
> >
> > PLUS, this clearance is above any obsticles. So if there
> are
> > trees or
> > buildings in the middle of the path, you'll need to be
> higher,
> > and yes,
> > hills and ground 'shape' will also affect this.
> >
> > 1km is definitely doable with a clear line of sight
> (including
> > fresnel
> > distances) in most countries with modest antennas.
> > Directional on one or
> > both will be preferred to reduce the quantity of noise
> > received from other
> > sources. I'm probably going to point the OP toward a set
> of
> > AP's with
> > sectoral Antennas for the fixed location, and an either an
> > omni or a mimo
> > radio mounted on each bus. Omni on both sides would
> > probably work as
> > well, but is more likely to have interference issues.
> >
> > On Tue, Oct 10, 2017 at 10:12 PM, James Cameron
> > <***@laptop.org> wrote:
> >
> > > With enough height above ground, and very flat ground,
> it
> > is doable. ;-)
> > >
> > > --
> > > James Cameron
> > > http://quozl.netrek.org/
> > > --
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> > >
> >
> >
> >
> > --
> > *Forrest Christian* *CEO**, PacketFlux Technologies, Inc.*
> > Tel: 406-449-3345 | Address: 3577 Countryside Road,
> Helena,
> > MT 59602
> > ***@imach.com | http://www.packetflux.com
> > <http://www.linkedin.com/in/fwchristian>
> > <http://facebook.com/packetflux>
> > <http://twitter.com/@packetflux>
> > --
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