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Any EE experts out there?

 
 
hermes
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      11-16-2005
(xposted due to small group sizes)

Question, what are the probabilities of getting a reliable signal with
the following circumstances:

Main Wifi transmission point is approx. 2/3 km from house. Signal points
downward toward nearby plaza with a 60 degree spread.

One building between line of sight and signal that I think is a couple
of stories short of the building where the wifi signal point emanates
(from roof-not positive on this-how critical is line of sight)

using primestar or similar dish antennae-home made-can put on roof of
house pointing to same direction of signal

using good wifi card with good reception range

users near plaza give various reports from flaky reception to reception
beyond plaza. one guy tells me he gets it from his house, even further
than I am, but do not know if this is reliable report.

Finally and most importantly, is there any way to determine if signal
can be had using signal strength meter or other equipment, without
setting up the dish to test it?
 
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hermes
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      11-16-2005
Change of Subject for the netcops out there

hermes <(E-Mail Removed)> wrote in news:dlft5s$7f3$1
@odin.weihenstephan.org:

> (xposted due to small group sizes)
>
> Question, what are the probabilities of getting a reliable signal with
> the following circumstances:
>
> Main Wifi transmission point is approx. 2/3 km from house. Signal

points
> downward toward nearby plaza with a 60 degree spread.
>
> One building between line of sight and signal that I think is a couple
> of stories short of the building where the wifi signal point emanates
> (from roof-not positive on this-how critical is line of sight)
>
> using primestar or similar dish antennae-home made-can put on roof of
> house pointing to same direction of signal
>
> using good wifi card with good reception range
>
> users near plaza give various reports from flaky reception to

reception
> beyond plaza. one guy tells me he gets it from his house, even further
> than I am, but do not know if this is reliable report.
>
> Finally and most importantly, is there any way to determine if signal
> can be had using signal strength meter or other equipment, without
> setting up the dish to test it?
>


 
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Jeff Liebermann
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      11-17-2005
On Wed, 16 Nov 2005 18:18:37 +0000 (UTC), hermes <(E-Mail Removed)>
wrote:

I got me a BSEE and I are an expert. Whatcha want?

>(xposted due to small group sizes)


Lousy reason. Maybe with a little effort, you can also work on an
appropriate subject line. I decide which questions are worth
answering by the subject line.

>Question, what are the probabilities of getting a reliable signal with
>the following circumstances:


Probability? Most of the time, wireless either works or it doesn't. A
flakey connection, that drifts in and out is not considered working. A
good rule of thumb is a minimum 20dB fade margin for the link which
will give about 99% reliability. (Notice I said minimum). 99% isn't
that great as it suggests roughly 3.6 full days of outage every year.

Reliability Fade Margin
90% 8 dB
99% 18 dB
99.9% 28 dB
99.99% 38 dB
99.999% 48 dB

>Main Wifi transmission point is approx. 2/3 km from house. Signal points
>downward toward nearby plaza with a 60 degree spread.


Lovely. Any particular reason you don't bother disclosing the details
of your "main wi-fi transmission point"? Little details like the make
and model, the type of coax, and the type of antenna are necessary to
calculate the path. 60 degree spread probably means 60dB -3dB
beamwidth. Vertical or Horizontal beamwidth? Without numbers, I
don't wanna bother doing the calcs.

Incidentally, if your "main wi-fi transmission point" antenna is a
high gain omnidirectional antenna, you're in trouble. The vertical
beamwidth of high gain omnis is quite narrow. You won't get anything
at -30 degrees down. All the RF is going over everyone's head.

>One building between line of sight and signal that I think is a couple
>of stories short of the building where the wifi signal point emanates
>(from roof-not positive on this-how critical is line of sight)


Line of sight is critical. NLOS is science fiction. You actually
need more than just line of sight. You need Fresnel Zone clearance at
the midpoint of the path.

>using primestar or similar dish antennae-home made-can put on roof of
>house pointing to same direction of signal


Yeah, you can use a Primstar or similar dish. Any clue what you're
going to use for a dish feed? You can't just hang a tin can or USB
radio at the focus and expect exemplary performance.

>using good wifi card with good reception range


Define "good"? Note that you can always trade reliability (fade
margin), range, and speed. How fast do you wanna go?

>users near plaza give various reports from flaky reception to reception
>beyond plaza. one guy tells me he gets it from his house, even further
>than I am, but do not know if this is reliable report.


Any reason not to supply numbers (distances)?

>Finally and most importantly, is there any way to determine if signal
>can be had using signal strength meter or other equipment, without
>setting up the dish to test it?


Netstumbler for Windoze.
Kismet for Linux.
Built in diagnostics or SNMP on your unspecified access point.


--
Jeff Liebermann http://www.velocityreviews.com/forums/(E-Mail Removed)-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
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hermes@god.net
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Posts: n/a
 
      11-18-2005
on Wed 16 Nov 2005 10:47:15p, Jeff Liebermann
<(E-Mail Removed)-cruz.ca.us> wrote in
news:(E-Mail Removed):

> On Wed, 16 Nov 2005 18:18:37 +0000 (UTC), hermes
> <(E-Mail Removed)> wrote:
>
> I got me a BSEE and I are an expert. Whatcha want?


How about a reply I can understand? If I could understand the
stuff you gave me, thanks, I wouldn't need to ask you,-I'd be in
Engynring skul myself.
>
>>(xposted due to small group sizes)

>
> Lousy reason. Maybe with a little effort, you can also work on
> an appropriate subject line. I decide which questions are worth
> answering by the subject line.


Yeah, I goofed on the subject line, I admit it.
>
>>Question, what are the probabilities of getting a reliable
>>signal with the following circumstances:

>
> Probability? Most of the time, wireless either works or it
> doesn't. A flakey connection, that drifts in and out is not
> considered working. A good rule of thumb is a minimum 20dB fade
> margin for the link which will give about 99% reliability.
> (Notice I said minimum). 99% isn't that great as it suggests
> roughly 3.6 full days of outage every year.
>
> Reliability Fade Margin
> 90% 8 dB
> 99% 18 dB
> 99.9% 28 dB
> 99.99% 38 dB
> 99.999% 48 dB
>
>>Main Wifi transmission point is approx. 2/3 km from house.
>>Signal points downward toward nearby plaza with a 60 degree
>>spread.

>
> Lovely. Any particular reason you don't bother disclosing the
> details of your "main wi-fi transmission point"? Little details
> like the make and model, the type of coax, and the type of
> antenna are necessary to calculate the path. 60 degree spread
> probably means 60dB -3dB beamwidth. Vertical or Horizontal
> beamwidth? Without numbers, I don't wanna bother doing the
> calcs.


Cuz I don't know them and the one guy who is an exec for the
project didn't seem too technically inclined either. I checked
again and yipee I DO have a line of sight to the antenna, I THINK.
There are about 5 antennas on the building, any idea what shape
this one might be? This is a municipal wifi transmission tower
meant for the city plaza yuppies to use their laptops. I just
happen to have a line of sight about .6 km from the building.

>
> Incidentally, if your "main wi-fi transmission point" antenna is
> a high gain omnidirectional antenna, you're in trouble. The
> vertical beamwidth of high gain omnis is quite narrow. You
> won't get anything at -30 degrees down. All the RF is going
> over everyone's head.


Two small dish antennas on roof, one tower about 6 feet high and a
foot in oval diameter, one rather smallish rectangle antenna about
3 feet high with a rectangular element about 2 feet by two feet.
This is from binocular observations as the people who run this
aren't too accessible.
>
>>One building between line of sight and signal that I think is a
>>couple of stories short of the building where the wifi signal
>>point emanates (from roof-not positive on this-how critical is
>>line of sight)

>
> Line of sight is critical. NLOS is science fiction. You
> actually need more than just line of sight. You need Fresnel
> Zone clearance at the midpoint of the path.


What the hell is Fresnel Zone clearance Dr. Spock? I have line of
sight, so my guess is a good antennae will boost the signal
enoughto get it reliably, but I am a novice, if it wasn't already
obvious, with a very small understanding of electronics and a
worse understanding of radio frequency stuff.
>
>>using primestar or similar dish antennae-home made-can put on
>>roof of house pointing to same direction of signal

>
> Yeah, you can use a Primstar or similar dish. Any clue what
> you're going to use for a dish feed? You can't just hang a tin
> can or USB radio at the focus and expect exemplary performance.


Yep, have instructions for building with tin can. Question, where
can I buy a used dish for cheap?

>
>>using good wifi card with good reception range

>
> Define "good"? Note that you can always trade reliability (fade
> margin), range, and speed. How fast do you wanna go?


Would be happy with even 1 MB /sec as I am on dialup now.
>
>>users near plaza give various reports from flaky reception to
>>reception beyond plaza. one guy tells me he gets it from his
>>house, even further than I am, but do not know if this is
>>reliable report.

>
> Any reason not to supply numbers (distances)?


Well these reports are not really judged reliable, but most users
are using standard laptops from about 100 yards, estimate.
>
>>Finally and most importantly, is there any way to determine if
>>signal can be had using signal strength meter or other
>>equipment, without setting up the dish to test it?

>
> Netstumbler for Windoze.
> Kismet for Linux.
> Built in diagnostics or SNMP on your unspecified access point.


I meant without buying wifi pci cards ahead of time. What
questions should I ask the tech people on this IF I can get to
talk to them? Thanks for your reply.

>
>


 
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Jeff Liebermann
Guest
Posts: n/a
 
      11-18-2005
On Fri, 18 Nov 2005 03:10:07 +0000 (UTC), "(E-Mail Removed)"
<(E-Mail Removed)> wrote:

>on Wed 16 Nov 2005 10:47:15p, Jeff Liebermann
><(E-Mail Removed)-cruz.ca.us> wrote in
>news:(E-Mail Removed) :
>
>> On Wed, 16 Nov 2005 18:18:37 +0000 (UTC), hermes
>> <(E-Mail Removed)> wrote:
>>
>> I got me a BSEE and I are an expert. Whatcha want?

>
>How about a reply I can understand? If I could understand the
>stuff you gave me, thanks, I wouldn't need to ask you,-I'd be in
>Engynring skul myself.


I charge extra for intelligible answers. If there's something you
don't understand, just ask and I'll either explain, or point you at an
appropriate online tutorial. Kindly disclose your educational level
and experience so I can package the responses accordingly. If you ask
for an EE to respond, you'll get an answer at the level of an EE.

>Cuz I don't know them and the one guy who is an exec for the
>project didn't seem too technically inclined either.


Guess. You'll be amazed at how close you can get. For example, the
list of hardware you currently have can easily be guessed by looking
at the serial number tag and disclosing the make and model. If you
don't know the coax cable type, just read the label on the coax. The
antenna can be roughly described by type and size.

>I checked
>again and yipee I DO have a line of sight to the antenna, I THINK.


Too much smog in the way? What's the problem? Moving obstructions?

>There are about 5 antennas on the building, any idea what shape
>this one might be? This is a municipal wifi transmission tower
>meant for the city plaza yuppies to use their laptops. I just
>happen to have a line of sight about .6 km from the building.


Post a photograph of the installation on some public web server. 5
antennas implies sector antennas. Usually there are only 3 or 4. Five
antennas is too much so there may be more than one service on the
tower. Hard to tell from here. How tall are the antennas? Are they
omnis (round tubular vertical) or panels? Just the antennas pointed
in your direction.

Gotta run. More later.
(chop...)

 
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Jeff Liebermann
Guest
Posts: n/a
 
      11-18-2005
On Fri, 18 Nov 2005 03:10:07 +0000 (UTC), "(E-Mail Removed)"
<(E-Mail Removed)> wrote:

(Blundering onward...)

>Two small dish antennas on roof,


Those are for the backhaul back to the ISP. Two dishes implies two
different service providers on the tower which explains the large
number (5) of antennas. Try to figure out which antenna is the one
your connection is using.

>one tower about 6 feet high and a
>foot in oval diameter, one rather smallish rectangle antenna about
>3 feet high with a rectangular element about 2 feet by two feet.


2ft by 2ft sounds like a panel antenna. However, at 2.4Ghz, an
antenna that size would have about 15dBi gain and be rather
directional. If it's pointed downward, it's intended to "illuminate"
a rather small area. You will have difficulties connecting to this
panel antenna as it offers very little to the sides and none from
behind.

>This is from binocular observations as the people who run this
>aren't too accessible.


Leave a note for them taped to the door or to the equipment asking for
them to call you. I've done this a few times and it's worked quite
well.

>What the hell is Fresnel Zone clearance Dr. Spock?


You're learning, Grasshopper. Fresnel Zone clearance is the radius
from the center line that you need in addition to line of sight to
insure that any objects inside the Fresnel Zone do not create edge
diffraction effects and trash the signel. At 0.6km and 2.4Ghz, it's
about 4 meters at midpoint. Mentally draw and 8 meter diameter circle
at the midpoint of your link. Do you have that much clearance?
http://terabeam.com/support/calculat...esnel-zone.php

>I have line of
>sight, so my guess is a good antennae will boost the signal
>enoughto get it reliably, but I am a novice, if it wasn't already
>obvious, with a very small understanding of electronics and a
>worse understanding of radio frequency stuff.


Assumption, the mother of all screwups. Yes, a good antenna will
probably get a good connection at 0.6km if the following criteria are
met.
1. The central access point antenna has some RF pointed in your
direction. This is rather dubious and the reason I want to see a
photo of the access point antennas.
2. There is no technology in place that restricts the distance one
can connect.
3. There is nothing in the Fresnel Zone to create problems.
4. The central access point has sufficient transmit power and receive
sensitivity. Some WISP providers intentionally reduce their tx power
and reduce their sensitivity so that they do not overlap the coverage
from adjacent radio systems.
5. There is no interference from other users on the same channels.
6. Your end has a sufficiently high gain antenna to yield a useable
signal level.

In this case, it's highly likely that it will work if #1 is met. At
0.6km, I like to run the numbers first to insure that it will work on
paper before you make the attempt. See below.

>Yep, have instructions for building with tin can. Question, where
>can I buy a used dish for cheap?


I'm partial to the Pacific Wireless dish antennas. They're the ones
that look like a wire barbeque grill. Solid dish antennas are better,
but far more expensive.
http://www.pacwireless.com/products/directional.shtml
$40 to $70 each depending on gain (15dBi, 19dBi, and 24dBi).

>Would be happy with even 1 MB /sec as I am on dialup now.


Nobody is happy with 1Mbit/sec. However, if this is a public
municipal hot spot, they probably limit the connection rate to either
5.5Mbits/sec or 11Mbits/sec for maximum compatibility with commodity
802.11b hardware. Assuming you're the only user, that will give you
perhaps 2Mbits/sec or 5Mbits/sec thruput. If the signal is weak, some
hot spots do not allow 1 and 2 mbit/sec connections because it hogs
too much air time.

>>>Finally and most importantly, is there any way to determine if
>>>signal can be had using signal strength meter or other
>>>equipment, without setting up the dish to test it?

>>
>> Netstumbler for Windoze.
>> Kismet for Linux.
>> Built in diagnostics or SNMP on your unspecified access point.

>
>I meant without buying wifi pci cards ahead of time.


Don't buy a wireless PCI card. Unless you can see the central access
point from wherever you plant your computah and can attach an antenna
fairly close to the computah, the coaxial cable losses will be
excessive. If the dish, panel, or tin can antenna is going on the
roof, your wireless client will need to be nearby to reduce the coax
losses. You may need to do some waterproofing and cabling. You can
also possibly use a USB radio if your total cable lengths are less
than 3 meters or your purchase overpriced USB line extenders.

I don't wanna recommend any hardware until I determine how much do it
thyself you are willing (and able) to do. If none, I suggest an
integrated wireless client such as:
| http://tranzeo.com/index.php?section..._section_id=92
The bottom of the line 15dBi may not be enough antenna gain to do the
job. It really depends on how much of the central access point signal
is pointed your direction.

Ummm... what country are you in? Regulatory differences have a big
effect on specs such as maximum allowed xmit power.

>What
>questions should I ask the tech people on this IF I can get to
>talk to them? Thanks for your reply.


That's a good question. Ask them:
1. Which antenna on the tower is the one pointed in your direction?
2. How much gain does the antenna have? How much downtilt in
degrees? Make an model of antenna would be nice.
3. How much coax cable loss is between the antenna and the radio.
4. What type of radio and approximately how much transmit power
(milliwatts or dBm is fine). Make and model would be nice. I can
guess the receiver sensitivity.
5. Do they support 802.11g speeds? If not, what are the allowed
connection speeds?

I'll do a dry run on the calcs to show you what I mean. The number
are guesses based on what you've already supplied. The central
antenna is apparently pointed downward rather than at the horizon
which means you won't have much gain in your direction. That will be
the major headache. I'll assume clear line of sight including the
Fresnel Zone. I'll also assume a 5.5Mbit/sec connection. The goal of
this exercise is to get more than 20dB fade margin.

Pluging the quesswork into:
http://www.terabeam.com/support/calculations/som.php
TX power = +15dBm
TX coax loss = 4dB (3ft LMR-240 plus a mess of connectors)
TX ant gain = 3dB (due to being off the side of the main pattern)
Distance = 0.6km (0.37 miles)
RX ant gain = +24dBi (biggest dish available)
RX coax loss = 4dB (assumes radio on roof)
RX sens = -85dBm (at 5.5Mbits/sec CCK)
This yields fade margin of 23.4dB which is fine. A smaller 19dBi dish
will also work with 20.4dB fade margin. However, a 15dBi dish or
panel will NOT work.

The obvious limiting factor on the above calculations is the antenna
gain and directionality of the access point panel antenna. My guesses
are totally arbitrary and are probably wrong. It may be better or it
may be much worse depending on which direction the antenna is pointed.

Incidentally, the Primestar dish idea will work, but you will need to
do some rather complex calculations, modeling, and testing to get
anything useful. Low gain (<10dBi) antennas are fairly easy. High
gain antennas are not.



--
Jeff Liebermann (E-Mail Removed)-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
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John Navas
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      11-18-2005
[POSTED TO alt.internet.wireless - REPLY ON USENET PLEASE]

In <dljgmb$38t$(E-Mail Removed)> on Fri, 18 Nov 2005 03:10:07 +0000
(UTC), "(E-Mail Removed)" <(E-Mail Removed)> wrote:

>What the hell is Fresnel Zone clearance Dr. Spock?


As always, "Google is your friend!"
<http://www.google.com/search?q=Fresnel%20Zone%20clearance>

>... Question, where
>can I buy a used dish for cheap?


Housewares dept.

--
Best regards, FAQ FOR CINGULAR WIRELESS
John Navas <http://en.wikibooks.org/wiki/Cingular_Wireless_FAQ>
MY HELP FOR CINGULAR GSM & SONY ERICSSON PHONES:
<http://navasgrp.home.att.net/#Cingular>
 
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John Navas
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Posts: n/a
 
      11-18-2005
[POSTED TO alt.internet.wireless - REPLY ON USENET PLEASE]

In <(E-Mail Removed)> on Fri, 18 Nov 2005 03:55:39
GMT, Jeff Liebermann <(E-Mail Removed)-cruz.ca.us> wrote:

>Post a photograph of the installation on some public web server. ...


e.g., <http://commons.wikimedia.org/>

--
Best regards, FAQ FOR CINGULAR WIRELESS
John Navas <http://en.wikibooks.org/wiki/Cingular_Wireless_FAQ>
MY HELP FOR CINGULAR GSM & SONY ERICSSON PHONES:
<http://navasgrp.home.att.net/#Cingular>
 
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hermes
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Posts: n/a
 
      11-18-2005
Jeff Liebermann <(E-Mail Removed)-cruz.ca.us> wrote in
news(E-Mail Removed):

> http://www.velocityreviews.com/forums/(E-Mail Removed)



Thank you very much Dr. Spock. I have some homework to do, so please
give me a few days; hope you are around then. At least I have an idea of
what I am up against now. Main thing is to find which antenna and
whether I can grab a slice of the signal or not (degree of tilt?).

Will report back when/if I can get some better information (can tell you
are indeed and expert-unlike so many pseudo experts out there).

 
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hermes
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      11-22-2005
Dr. Spoke, today I found out the connections are limited to 512KB/second
and that they have NO wep key-no security, so I would have to set up a
VPN, whatever the hell that is (have a rough idea). So, sounds like it
is not worth the effort; wish I had found this out sooner. Thanks
again for the tutorial on wifi transmission/reception.

Jeff Liebermann <(E-Mail Removed)-cruz.ca.us> wrote in
news(E-Mail Removed):

> On Fri, 18 Nov 2005 03:10:07 +0000 (UTC), "(E-Mail Removed)"
> <(E-Mail Removed)> wrote:
>
> (Blundering onward...)
>
>>Two small dish antennas on roof,

>
> Those are for the backhaul back to the ISP. Two dishes implies two
> different service providers on the tower which explains the large
> number (5) of antennas. Try to figure out which antenna is the one
> your connection is using.
>

<snip>
 
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