Re: Is there some kind of full duplex wireless software...
On Aug 27, 2004, at 12:06 PM, Day Brown wrote:
I thot it wuz obvious in the phrase, 'difficult terrain' and other
points in my postings, that I *DO NOT* have line of sight.
I live in the Ozarks, have been poking into this for a while. There is
an outfit that offers hi-speed wireless, but it is using 900mhz
transmitters, which wont even penetrate the canopy, much less get down
into any of the hollows. 802 and *all* of the other commercially
available wireless network equipment is useless. People cant even get
UHF TV unless they live on a ridgetop.
You're still missing my point. RF doesn't "change rules" when you
switch to spread spectrum or any other emission standard.
If 900MHz commercial gear from a professional company with towers and
high sites won't "get through the canopy" nothing you can come up with
that will plug into a sound card will, surely. Unless you're running
more power than they are, and I assume from your notes that you're
attempting this with off-the-shelf gear and you don't have RF power
amplifier design experience nor the gear to properly test one. (Let
alone the legalities.)
For high speed data, since you need higher frequencies to lower the RF
bandwidth requirements, the fix is to put up a tower - ABOVE the
canopy. The fix for not having line of sight at VHF and above is to
figure out how to GET line of sight.
Your choice of frequency dictates how wide in frequency your signal
needs to be for a given data rate.
All I wanted to know was, how to interface the analogue signal. It
seemed evident that the capablilities of the sound card was already
there to do that, and work with the kind of bandwidth that standard FM
stereo transmitter designs already know how to produce. If anyone here
knew of software to do that, I think we would have heard of it by now.
Interface the analogue signal to what? That's the part I've been
asking... you mentioned a "chip". Okay, let's just say this magical
chip exists that happens to take in any signal you give it an
beautifully put it out into the electromagnetic world of RF. What's
your data speed requirement? 1 Mb/s? 2? 10? 100?
If anyone does have a clue, I'm sure they'll send me something off
list, so I'll unsub and quit bothering you.
I think a lot of people here have a clue and have been doing RF design
of systems to transmit data for decades. They're probably hanging back
and letting this conversation go on wondering if enough information
will emerge to offer you any help. In fact, I bet there's a bunch of
people who, presented a terrain map, the locations of the commercial
wireless 900MHz guy's tower, and about ten minutes could define two or
three good ways to get your Internet service delivered to your
"difficult" location. Or they could tell you "it can't be done without
a hop-point somehere over *here* on this map".
No matter what way you cut it, it's a very rare chance that anything
you could design will beat the performance of commercially available
systems. If the commercial 900MHz guys can't get to you, nothing you
can build is going to fix that. Time better spent would be fixing the
line of sight problem by either getting the antennas up out of the
trees, or figuring out a multiple-hop path where you could "shoot" to
somewhere that CAN see the 900 MHz commercial guys. You probably still
need to get above the trees for that!
There's whole bunches of very good software packages out there (mostly
commercial, but one free one) that do RF path prediction that are very
accurate. From your first messages about frequency, you're obviously
GUESSING. There's no need to do that.
Ask the 900 MHz guys for a prediction plot for your location and then
figure out how to augment your setup to reach them. (Think in terms of
a business opportunity too. If you put up a tower that gets you above
the canopy to "see" their feed site, can they then use your tower to
extend their coverage to your entire neighborhood? If so... perhaps
you can work out a deal for free Internet, just for the cost of a small
tower in the trees in your backyard. Heck, can you put the antennas IN
the trees?)
What I'm saying (and have been saying all along) is that YES! there
definitely IS a way to get you Internet service in the boonies, but
you're going about it the REALLY REALLY HARD WAY if you're designing RF
gear.
Back up 1000' and look at it from a different perspective.
A PC and magic "chip" are probably not the cheapest and most reliable
answer. RF engineering using well-known math for the given
requirements is.
Trust me, you're not bothering me at all -- I'm just trying to help you
get from "voodoo engineering" to something that will actually WORK and
is practical. ;-)
--
Nate Duehr, nate@natetech.com
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