Stupid Wifi Propagation Q ;-)

I've read enough abt wifi propagation technicals to go blind, but
cannot find any hands-on insight regarding:

What practical outdoor LOS ranges have been reliably obtained with
802.11g beyond the usual 1,000 ft, if any, using only a high-gain
directional ant at the AP & no extra CPE (i.e., only a laptop 100mw PCI
card & its typical display-cover-mounted diversity ant)? With and/or
without a bidirectional amp at the AP?

ISTM that with, say, a 17db narrow-beam ant exhibits its gain in both
directions, the major factor wld be the noise floor (s/n ratio),
ignoring other propagation issues for the moment? I'm in a rural area
on a hill without much noise & wish to experiment, but wld like to know
what general firsthand results hv been before buying a costly ant to
reinvent a wheel.

The overall interest is creation of a distant hotspot (no nearby
coverage), at a location where nothing may be installed. I know
there's no such thing as "a simple question" in RF propagation & am
only looking for seasoned generalizations to decide whether further
pursuit & survey is worthwhile.

(E-Mail Removed) wrote:
> I've read enough abt wifi propagation technicals to go blind, but
> cannot find any hands-on insight regarding:
>
> What practical outdoor LOS ranges have been reliably obtained with
> 802.11g beyond the usual 1,000 ft, if any, using only a high-gain
> directional ant at the AP & no extra CPE (i.e., only a laptop 100mw
> PCI card & its typical display-cover-mounted diversity ant)? With
> and/or without a bidirectional amp at the AP?
>
> ISTM that with, say, a 17db narrow-beam ant exhibits its gain in both
> directions, the major factor wld be the noise floor (s/n ratio),
> ignoring other propagation issues for the moment? I'm in a rural area
> on a hill without much noise & wish to experiment, but wld like to
> know what general firsthand results hv been before buying a costly
> ant to reinvent a wheel.
>
> The overall interest is creation of a distant hotspot (no nearby
> coverage), at a location where nothing may be installed. I know
> there's no such thing as "a simple question" in RF propagation & am
> only looking for seasoned generalizations to decide whether further
> pursuit & survey is worthwhile.

Consider doing it the rather easy and cheap way, and your situation sounds
perfect for it...two separate wireless systems at each end, and a second set
of ap's in bridge mode between the two areas with high gain antennas to make
it basically one network with seperate segments.. We do that to link
multiple rural areas (think of it as a bead string bead string bead string
etc, rather than one bead and a bunch of strings. Works over hills using
solar powered bridges too.

Peter Pan wrote:

> Consider doing it the rather easy and cheap way, and your situation
sounds
> perfect for it...two separate wireless systems at each end,

You didn't read the post, and aren't responding to it's Q, either. The
post states that nothing may be installed at the targeted site.

Dont be at all surprised when you now find the response to your post quite
"limited".


<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ups.com...
> Peter Pan wrote:
>
> > Consider doing it the rather easy and cheap way, and your situation
> sounds
> > perfect for it...two separate wireless systems at each end,
>
> You didn't read the post, and aren't responding to it's Q, either. The
> post states that nothing may be installed at the targeted site.
>

(E-Mail Removed) wrote:
> Peter Pan wrote:
>
>> Consider doing it the rather easy and cheap way, and your situation
>> sounds perfect for it...two separate wireless systems at each end,
>
> You didn't read the post, and aren't responding to it's Q, either.
> The post states that nothing may be installed at the targeted site.

fraid I did.. it said:
What practical outdoor LOS ranges have been reliably obtained with
802.11g beyond the usual 1,000 ft, if any, using only a high-gain
directional ant at the AP & no extra CPE (i.e., only a laptop 100mw PCI
card & its typical display-cover-mounted diversity ant)? With and/or
without a bidirectional amp at the AP?

See the question marks? That usually means you are asking a question...

On 1 Feb 2005 13:59:01 -0800, (E-Mail Removed) wrote:

>I've read enough abt wifi propagation technicals to go blind, but
>cannot find any hands-on insight regarding:

That's because all the other RF engineers have gone blind, retired, or
gone insane. RF does that to you.

>What practical outdoor LOS ranges have been reliably obtained with
>802.11g beyond the usual 1,000 ft, if any, using only a high-gain
>directional ant at the AP & no extra CPE (i.e., only a laptop 100mw PCI
>card & its typical display-cover-mounted diversity ant)? With and/or
>without a bidirectional amp at the AP?

Well, I'm a big believer in calculations, so let's try the numbers
first before we degenerate into anecdotal experience. I'm going to
make a big assumption here, that the Tx power is identical at both
ends. Cranking up the power on the wired end makes no sense if it
also can't hear the CPE radio. I'll assume 100mw (+20dBm) on both
ends.

This is for a DI-624 radio. I'll assume that you want about
9Mbits/sec performance which is -87dBm sensitivity for 1*10^5 BER (bit
error rate).
* 54Mbps OFDM, 10% PER, -68dBm)
* 48Mbps OFDM, 10% PER, -68dBm)
* 36Mbps OFDM, 10% PER, -75dBm)
* 24Mbps OFDM, 10% PER, -79dBm)
* 18Mbps OFDM, 10% PER, -82dBm)
* 12Mbps OFDM, 10% PER, -84dBm)
* 11Mbps CCK, 8% PER, -82dBm)
* 9Mbps OFDM, 10% PER, -87dBm)
* 6Mbps OFDM, 10% PER, -88dBm)
* 5.5Mbps CCK, 8% PER, -85dBm)
* 2Mbps QPSK, 8% PER, -86dBm)
* 1Mbps BPSK, 8% PER, -89dBm)

Starting at the wired end:
TX Power : +20dBm
TX Coax Loss : -6dBm
TX Antenna gain : +17dBm
Path Loss : unknown
RX Antenna gain : -4dBm
RX Coax Loss : 0
RX sensitivity : -87dbm

In order for this to work, you will want about 20dB of fade margin.
More would be better, but 20dB is a good target value. Going to:
http://www.ydi.com/calculation/som.php
I pound in the known numbers and tinker with the range until I get
20dB of fade margin. That yields 0.33 miles or about 2000ft.

>ISTM that with, say, a 17db narrow-beam ant exhibits its gain in both
>directions, the major factor wld be the noise floor (s/n ratio),
>ignoring other propagation issues for the moment?

I have no idea what your talking about here. The noise floor is
determined by the receiver bandwidth, temperature, and Boltzman's
Constant. If you want to throw in exact receiver calculations, I can
do that, but I don't think that's what you're looking for. It's also
hard to ignore propogation issues as that's probably the major
consideration for range and coverage.

Blundering onward, a 17dBi antenna has a finite -3db beamwidth.
That's about 20 degrees for a panel and 16 degrees for a dish. At
2000ft and a 16 degree beamwidth, you'll have a coverage width of
about 570ft. If this is the approximate width of the area you want to
cover, such a dish might work.

>I'm in a rural area
>on a hill without much noise & wish to experiment, but wld like to know
>what general firsthand results hv been before buying a costly ant to
>reinvent a wheel.

That's why I threw in the calculations. If the numbers don't work on
paper, they won't work when your throw your system together.

>The overall interest is creation of a distant hotspot (no nearby
>coverage), at a location where nothing may be installed.

Not even solar powered? I've done a few of those. They're fairly
easy as many access points will run on a wide range of DC input
voltages. For example, the WRT54G will run from 4-15VDC.

>I know
>there's no such thing as "a simple question" in RF propagation & am
>only looking for seasoned generalizations to decide whether further
>pursuit & survey is worthwhile.

Seasoned? My cardiologist insists that I cut down on spicy things.
However, it doesn't matter as I don't salt my generalizations.

There are many WISP's (wireless internet service providers) that are
sorta doing what you describe. From a hilltop or mountain, they
illuminate a sector with (you guessed it) as sector antenna. 90 and
120 degree sectors are common. However, they also make no attempt to
talk to laptops directly. Invariably, that involves going through
walls, trees, bushes, building, etc, that block the path. Laptop
antennas are also seriously lacking in gain. They usually install
client radios and antennas on the roof, where the view is better.

Good luck, whatever you're doing...

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558

(E-Mail Removed) wrote:
>I've read enough abt wifi propagation technicals to go blind, but
>cannot find any hands-on insight regarding:

It depends...

And it might cost you a couple hundred bucks to figure out *precisely*
how much it depends and on what.

>What practical outdoor LOS ranges have been reliably obtained with
>802.11g beyond the usual 1,000 ft, if any, using only a high-gain

That is impossible to answer in any generic way. How many buildings?
How many trees? How high are the antennas? What other kinds of
obstructions and what other kinds of reflections can one expect?

The only one reading this that can do a path study, is you.

>directional ant at the AP & no extra CPE (i.e., only a laptop 100mw PCI
>card & its typical display-cover-mounted diversity ant)? With and/or
>without a bidirectional amp at the AP?

The bidirectional amp probably will not be as useful as you
might expect, except under certain conditions.

The transmit amp will very definitely increase the range covered
by the transmitter. But the receive side does not have the same
effect, necessarily.

If the noise figure and antenna cable losses are small on the
existing receiver, adding a 18 dB receive amp (as one example)
increases the noise by the same 18 dB that it increases the
signal, and you gain exactly nothing. If, however, you can mount
the amp right at the antenna, before the feedline, there will be
an improvement roughly the same as the loss in the feedline. So
if the feedline is short, that's a waste of money... but it might
be very well spent if you have an outdoor antenna with a long run
of feedline.

However, a well engineered antenna is going to be a *big*
improvement. For a relatively small chunk of change you can get
an antenna that will provide 20 dB or so of gain. However,
"well engineered" is the key to it! Low loss feedline is
expensive, and anything else makes it all a futile waste of
resources.

>ISTM that with, say, a 17db narrow-beam ant exhibits its gain in both
>directions, the major factor wld be the noise floor (s/n ratio),
>ignoring other propagation issues for the moment? I'm in a rural area
>on a hill without much noise & wish to experiment, but wld like to know
>what general firsthand results hv been before buying a costly ant to
>reinvent a wheel.

Antennas are where it's at. And yes they provide gain in both
directions. (Being on top of a hill means there would be *more*
noise, BTW, not less.)

>The overall interest is creation of a distant hotspot (no nearby
>coverage), at a location where nothing may be installed. I know
>there's no such thing as "a simple question" in RF propagation & am
>only looking for seasoned generalizations to decide whether further
>pursuit & survey is worthwhile.

What do you mean "nothing may be installed"??? That's nonsense if
*you* are going to be there with a laptop!

But... consider what else, besides the laptop, can be
temporarily installed! I've seen someone say that a LinkSys
WRT54G can run on "anything from 5 to 12 VDC". Hmmm... Like a
6 volt lantern battery, for example. Or a rechargable lead-acid
6 volt battery (for motorcycles). (Or the 12 vdc system in the
vehicle you are driving, if you are careful about how it's
done.)

So what you need is a pair of good antennas. Install one on
your hilltop location attached to your existing AP and point it
at your desired hotspot. Rig up a box with a 6 volt battery, a
WRT54G, and an antenna on a tripod. Load Satori firmware into
the WRT54G, and bingo you have a repeater. Or you can just use
it as is by connecting to it with wired ethernet.

My guess is that the WRT54G is only one of many units that could
be used.

--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) (E-Mail Removed)

On Tue, 01 Feb 2005 18:24:26 -0900, (E-Mail Removed) (Floyd L.
Davidson) wrote:

>I've seen someone say that a LinkSys
>WRT54G can run on "anything from 5 to 12 VDC". Hmmm... Like a
>6 volt lantern battery, for example. Or a rechargable lead-acid
>6 volt battery (for motorcycles). (Or the 12 vdc system in the
>vehicle you are driving, if you are careful about how it's
>done.)

That was me. I did my testing with a BEFW11S4 and a WAP11v1.1, not a
WRT54G. I do have one in the office and can verify that it works with
the WRT54G (later)
http://www.LearnByDestroying/pics/dr.../low-volt.html
That's my BEFW11S4 running just fine on 3.5VDC. Basically, the
internal circuitry runs on 3.3VDC (7V full scale on meter). Add a few
tenths of a volt for the LDO switching regulator and it will run just
fine. Some board mutations apparently have a series diode for reverse
polarity and idiot protection. That will make the minimum voltage
about 3.9VDC. I think a good safe minimum voltage is about 5VDC.
That's what the WRT54Gv1.0 ran on.

The upper end is limited by the regulator max input voltage and the
maximum voltage on the electrolytic capacitors. The regulator will do
about 25VDC. The electrolytics are rated at 25VDC. Therefore, it
should work up to 25VDC, but that's way too close to the rated maxima
for comfort. Methinks 18-20VDC max is a good guess.

I suspect other wireless devices with similar switching regulators
have a similarly wide operating voltage range.



--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558

Jeff Liebermann <(E-Mail Removed)> wrote:
>On Tue, 01 Feb 2005 18:24:26 -0900, (E-Mail Removed) (Floyd L.
>Davidson) wrote:
>
>>I've seen someone say that a LinkSys
>>WRT54G can run on "anything from 5 to 12 VDC". Hmmm... Like a
>>6 volt lantern battery, for example. Or a rechargable lead-acid
>>6 volt battery (for motorcycles). (Or the 12 vdc system in the
>>vehicle you are driving, if you are careful about how it's
>>done.)
>
>That was me. I did my testing with a BEFW11S4 and a WAP11v1.1, not a
>WRT54G. I do have one in the office and can verify that it works with
>the WRT54G (later)

Thanks Jeff! Not just for the initial mention, which obviously
got my attention to put it mildly, but also for this added info.

I wasn't sure what kind of a regulator was being used, and
that's why I kind of hedged a bit above and said "Or the 12 vdc
.... if...". With a switching regulator that will handle 25
volts, one need not be too worried, and I'd expect it would work
fairly well directly off a 12 volts system in a car.

> http://www.LearnByDestroying/pics/dr.../low-volt.html

http://members.cruzio.com/~jeffl//pi.../low-volt.html

>That's my BEFW11S4 running just fine on 3.5VDC. Basically, the

....

That answered every question that I had. I've been thinking about
something similar to the OP's description, except with a fairly mobile
remote unit. The immediate thing that caught my attention was the
idea that one of these WRT54G units could be battery operated from
a vehicle, and with 3rd party firmware act as a repeater. That means
the laptop itself need only be within range of the WRT54G, which can
have a high gain external antenna.

Your information is very useful!

--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) (E-Mail Removed)

Where does one find the Satori firmware? Ive seen it referenced twice in the
last 2 days and am interested in seeing what it is all about. Thanks


"Floyd L. Davidson" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> (E-Mail Removed) wrote:
> >I've read enough abt wifi propagation technicals to go blind, but
> >cannot find any hands-on insight regarding:
>
> It depends...
>
> And it might cost you a couple hundred bucks to figure out *precisely*
> how much it depends and on what.
>
> >What practical outdoor LOS ranges have been reliably obtained with
> >802.11g beyond the usual 1,000 ft, if any, using only a high-gain
>
> That is impossible to answer in any generic way. How many buildings?
> How many trees? How high are the antennas? What other kinds of
> obstructions and what other kinds of reflections can one expect?
>
> The only one reading this that can do a path study, is you.
>
> >directional ant at the AP & no extra CPE (i.e., only a laptop 100mw PCI
> >card & its typical display-cover-mounted diversity ant)? With and/or
> >without a bidirectional amp at the AP?
>
> The bidirectional amp probably will not be as useful as you
> might expect, except under certain conditions.
>
> The transmit amp will very definitely increase the range covered
> by the transmitter. But the receive side does not have the same
> effect, necessarily.
>
> If the noise figure and antenna cable losses are small on the
> existing receiver, adding a 18 dB receive amp (as one example)
> increases the noise by the same 18 dB that it increases the
> signal, and you gain exactly nothing. If, however, you can mount
> the amp right at the antenna, before the feedline, there will be
> an improvement roughly the same as the loss in the feedline. So
> if the feedline is short, that's a waste of money... but it might
> be very well spent if you have an outdoor antenna with a long run
> of feedline.
>
> However, a well engineered antenna is going to be a *big*
> improvement. For a relatively small chunk of change you can get
> an antenna that will provide 20 dB or so of gain. However,
> "well engineered" is the key to it! Low loss feedline is
> expensive, and anything else makes it all a futile waste of
> resources.
>
> >ISTM that with, say, a 17db narrow-beam ant exhibits its gain in both
> >directions, the major factor wld be the noise floor (s/n ratio),
> >ignoring other propagation issues for the moment? I'm in a rural area
> >on a hill without much noise & wish to experiment, but wld like to know
> >what general firsthand results hv been before buying a costly ant to
> >reinvent a wheel.
>
> Antennas are where it's at. And yes they provide gain in both
> directions. (Being on top of a hill means there would be *more*
> noise, BTW, not less.)
>
> >The overall interest is creation of a distant hotspot (no nearby
> >coverage), at a location where nothing may be installed. I know
> >there's no such thing as "a simple question" in RF propagation & am
> >only looking for seasoned generalizations to decide whether further
> >pursuit & survey is worthwhile.
>
> What do you mean "nothing may be installed"??? That's nonsense if
> *you* are going to be there with a laptop!
>
> But... consider what else, besides the laptop, can be
> temporarily installed! I've seen someone say that a LinkSys
> WRT54G can run on "anything from 5 to 12 VDC". Hmmm... Like a
> 6 volt lantern battery, for example. Or a rechargable lead-acid
> 6 volt battery (for motorcycles). (Or the 12 vdc system in the
> vehicle you are driving, if you are careful about how it's
> done.)
>
> So what you need is a pair of good antennas. Install one on
> your hilltop location attached to your existing AP and point it
> at your desired hotspot. Rig up a box with a 6 volt battery, a
> WRT54G, and an antenna on a tripod. Load Satori firmware into
> the WRT54G, and bingo you have a repeater. Or you can just use
> it as is by connecting to it with wired ethernet.
>
> My guess is that the WRT54G is only one of many units that could
> be used.
>
> --
> Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
> Ukpeagvik (Barrow, Alaska) (E-Mail Removed)