I'm getting inconsistent results with Linksys WAP54G over about 400m
with bursts of high speed then periods of nothing.

Both Linksys are set to repeater mode. 

Far end has cantenna on one of the aerials and the other aerial is
removed. Ethernet to hub.

Near end have tried with both aerials on and also one aerial to
cantenna with other standard aerial picking up from notebook.

(view with fixed font for clarity)

  ((   )) represent wireless signal

Home
Notebook ))  ((Near Linksys ))Cantenna or standard aerial

~300m        | House   
    Tree    |
~380m        Over an office roof
    Far Linksys )) Cantenna
Office           Hub

I seem to get less dropouts when the near (home) linksys has the two
supplied aerials fitted and placed in the window but a low speed.  The
fastest results are when one aerial is connected to the cantenna at
home but then it will then drop/lock out.

The aerials are set to diversity mode and I wonder whether it can get
confused as to whether it is setting the aerials speeds to the
notebook or to the distant cantenna.

The "obstruction" of House and Tree is about 2 - 3 metres horizontally
and the office roof is about 1m vertically.

Any suggestions welcomed.

Thanks

Show quote Hide quote It sounds like a weird config. Ordinarily when you put a WAP in
repeater mode
the ethernet is disabled but you say the remote site connects to a hub
via ethernet.
Im really surprised it works at all that way, but then again I aint
seen everything.
If you want wireless at the home end then I would use AP mode there
and AP
Client mode at the Remote but his may depend on the number of PCs at
the remote site.
AP Client usually only handles "A Client", not multiples unless a
router is involved or you can use
bridge mode on both ends but neither end will have wireless client
capability unless you add an AP on that end.
Unless you can get the signals out of the trees and house ( a clear
Fresnel zone) then you may
continue to have intermittent type problems.

On Mon, 7 Mar 2005 15:10:09 -0600, "Airhead"
<campb***@alliancecable.net> wrote:

Show quoteHide quoteSeems as though it has some dual mode abiltiy then?

I definitely want to connect the Remote Linksys to the wired office
network.  Only a handful of PC's and a couple of file servers but it
would be great to:

    a) piggy back onto the office broadband
    b) access the office systems

from home.

I'm not using AP Client mode at all.

The farmer won't move his house :(

Perhaps I have asked the question the wrong way round.  What do you
suggest is the right  way to set up the devices for:

A couple of wireless laptops at home so that they can see eachother
and both connect to the office network (400m) away with line of sight?

On Mon, 7 Mar 2005 15:10:09 -0600, "Airhead"
<campb***@alliancecable.net> wrote:


Am I correct in understanding that in bridge mode no-one in the middle
will be able to jump into my network?  If so that is a good thing as I
would prefer to have that security.

On Mon, 07 Mar 2005 14:20:52 GMT, intothe***@hotmail.com (Tony Lewis)
wrote:

How long are the bursts of high speed?  How long are the times with no
traffic?  Just guess at approximate values.  The times are very useful
for determining a possible source of interference? 

Have you tried using different channels?

Bad idea for initial testing.  Set it to the transparent bridge mode.
That will keep other wireless users and devices from associating and
only allow traffic between endpoints.

I'm guessing that you're at the bitter edge of marginal performance.
If I knew how much pigtail and coax cable you had between the WAP54G
and antenna, I can make a better guess.  Let's play with the numbers
and please correct my guesswork.

I'll guess that you have the cantenna end connected with a rather long
and thin (LMR-240) pigtail with about 6dB loss including connectors.
The cantenna is good for about 8dBi gain, if built correctly.  I have
no clue how fast your burst of performance are running and therefore
cannot guess at what association speed you're running.  I'll assume
16Mbits/sec OFDM for a receiver sensitivity of -88dBm.  The stock
rubber ducky antennas have about 0dBi gain.  In theory, they should be
more, but that's what I've measured.  Grinding the numbers.

  TX power =  +15dBm   (Cantenna end)
  TX coax loss = 6dBm
  TX antenna gain = +8dBi
  Distance = 400 meters (0.25 miles)
  RX antenna gain = 0dBi
  RX coax loss = 0.5dBm
  RX sensitivity = -88dBm  (6Mbits/sec OFDM)
  Desired fade margin = ????

Plugging into:
  http://www.terabeam.com/support/calculations/som.php
I get a fade margin of:  10.3 dB which is awful.  The way fade margin
works is that the rated sensitivity of -88dBm will yield about 10^5
BER (bit error rate) which is a rather flakey and useless connection.
You have a fade margin of 10dB (about 10 times) more than that
resulting in a substantially better BER.  However, the errors will
still be there and can be statistically estimated.
  Fade Margin    Reliability
  10 dB           90
  20              99
  30              99.9
  40              99.99

However, this is under ideal conditions and does not include the
attenuation of the house and tree as well as the fact that they're in
the Fresnel zone and will cause some signal to be diverted via
diffraction.  Without a description, I can't offer a guess as to how
much additional path loss these will present, but I'm fairly sure it
will be more than 10dB.  In other words, this link is not going to
work reliably.

Show quoteHide quoteIn order of importance.

1.  Get line of sight.  Relocate the antennas so that there's nothing
in the way and that you have Fresnel zone clearance.  If you can't get
LOS and clearance, you will have flakey performance (guaranteed).

2.  Get bigger antennas.  You want to have at least 20dB fade margin
with the above calculations.  My guess is that you need at least
+15dBi gain antennas at both ends.  If you have an aesthetics problem,
you might want to try add on reflectors:
  http://www.freeantennas.com/products.htm

3.  Turn off the repeater mode and use the bridge mode for testing.

4.  Try a different channel in case you are having intereference
problems.

5.  Position antennas as close to WAP54G to reduce coax losses.

6.  Fix the speed to 6MBits/sec OFDM.  Do not let it rate adjust
itself.  AP's spend an awful long time adjusting their speeds for
noisy connections.

7.  Run the numbers.  Aim for 20dB fade margin.  It's not that
difficult.  If it doesn't work on paper, it's not going to work on the
air.  Actually, I'm rather amazed that it works at all with your
existing configuration.

On Tue, 08 Mar 2005 09:58:32 -0800, Jeff Liebermann
<je***@comix.santa-cruz.ca.us> wrote:

<snipped>
A lot to digest there Jeff and it'll be a few days before I will be
able to test out and report back.

A couple of quick comments:

1) Have tried to keep coax cable lengths down so that there is a
theoretical net gain

2) I have no latitude to change the horizontal path.  It is the only
clear line of sight I have.  I could go higher but cable lengths will
go up (I'm already on a shed roof the office end to get a line of
sight).

3) I've hit around 400kbits/sec (with cantennas both ends) which would
be acceptable if sustained.  Try to download a 3mb file for testing
(from the LAN not the net) and after a couple of attempts the systems
seem to lock and do not recover.  I then have to revert to the "rubber
duckies" in the window.   Typically then I'm down to 100kbit/sec but
sustainable.

4) There is another cantenna arrangement about 30 metres to one side
at the office end.  The office end cantenna is pointing at 90 deg to
it but I'm sure it is able to pick up some signal as I can with my
laptop if standing under the aerial.

5) Bridge mode seems my next test with probable channel change.

I'll report back.

On Wed, 09 Mar 2005 12:21:13 GMT, intothe***@hotmail.com (Tony Lewis)
wrote:

How much coax in meters?  What type of coax?  I like numbers, not
vague descriptions.

Think about mounting the WAP54G in an outdoor box to reduce the coax
length.  See:
  http://www.sveasoft.com/articles/armored/
  (see tiny "next" in lower right of page)
for the general idea.  One correction.  The WAP54G and WRT54G will run
on anything between about 4VDC and 15VDC.  No need for PoE (power over
Ethernet) converter.  Just run two extra wires from the CAT5 cable to
power and ground from the 12VDC wall wart.  There will be cable loss
but the WRT54G power supply regulator will not care.

That's about what you will get at the very slowest speed of 1Mbit/sec.
The access point has decided that the path is so bad, that it has
slowed down to it's slowest data rate in a heroic effort to maintain
communcations.

Yep.  That's usually what happens.

Actually, you're down to about 450kbits/sec nominal thruput with a
huge number of lost packets and resends.  I'm amazed that it's
"sustainable" as it usually hangs if the packet loss is excessive.
Try playing some 64kbit/sec streaming audio through the link and you
can actually hear the stalls and resends.

Oh-oh.  Trouble.  Try to identify (with Netstumbler) the channel that
they're using and find another.  Cantennas are NOT very directional:
  http://www.learnbydestroying.com/pics/antennas/coffee2400/index.html
At 90 degress, you're approximately either -8dB or -15dB down
depending on orientation.

I goofed.  I thought you had two WAP54G radios and didn't see the
laptop as one end.  That cannot be used in the bridge mode.  The
WAP54G has to be in the access point mode.  Try a different channel
(1, 6 or 11) but I don't think that will help.  You need a better RF
path.

On Wed, 09 Mar 2005 09:03:12 -0800, Jeff Liebermann
<je***@comix.santa-cruz.ca.us> wrote:

We're both on Channel 11

I was planning to initially use an ethernet cable to connect one
laptop to the WAP54G at home to test.  I presume that will allow the
WAP54G to be in bridge mode.  If all works out ok I'll put in another
access point in normal access point mode then connect that to the
WAP54G so that both laptops can either talk to eachother or to the
office lan/broadband.

The WAP54Gs have dual aerials currently set to diversity mode.  With
bridge mode I plan to set the aerial to only the one connected to the
cantenna.

I've tried to find an answer to a relative straightforward question
but there is too much noise - what is repeater mode for if it is not
for what I am doing?

On Wed, 09 Mar 2005 21:03:01 GMT, intothe***@hotmail.com (Tony Lewis)
wrote:

Bad idea.  Move to either ch 1 or ch 6.

Yes.  You usually need two identical radios to play transparent bridge
(there are exceptions).  With a transparent bridge, you can connect up
to 253 computahs at the remote end.  Each will get it's own IP address
from the DHCP server. 

That will work.

It doesn't matter.  The radio will select its favorite and antenna and
stay with it until it loses the connection.  I still suggest you get a
"real" antenna or two.  It's the lack of antenna gain that's causing
the crappy connectivity.

This is not an easy question but I'll try to keep it simple.

WDS (wireless distribution service) is a feature where an
infrastructure access point can also act simultaneously as a
transparent bridge. 
Wireless clients can connect to a WAP54G at the office normally.
Wireless clients can connect to a WAP54G at the house normally.
The house WAP54G can also transparent bridge to the office.
Therefore, wireless (and wired) clients at the house, can connect
through the WDS bridge (repeater) maze to the office WAP54G, to a
router, and finally to the internet.  This may actually work for you.

However, all is not perfect.  There are problems.

Your connection between the house and office is so bad, that you're
going to have very poor thruput.  Half of that will make it even
worse.  You should make an effort to improve the path, antenna gain,
avoid the other users on ch 11, and thereby improve the thruput.  Once
you get it at about twice your DSL or cable modem speed, then half of
that will not be detrimental.

Another problem are the antennas at the house WAP54G.  You could just
mount the WAP54G on the roof, run power, solar, battery, AC, whatever,
on the roof, and run everything from the house via wireless.
Hopefully, the path between the house WAP54G and the office WAP54G
will be good enough to fix the performance problem.  However, the
directional antenna necessary to do that at the house may not have any
coverage in the downward direction into the house.  Installing a 2nd
antenna pointed downward on the "other" antenna port seems an obvious
fix, but there's a problem.  It takes time for the radio to decide to
switch between antennas and that introduces some rather large delays.
You can do the repeater thing with one antenna, but don't try it with
diversity enabled (i.e. 2 antennas).

I know of some tricks using a Wilkinson splitter/combiner that will
sorta solve the antenna problem, but you need to have at least 4dB of
surplus fade margin available.  You don't have that luxury so I won't
suggest it.  Anyway, if you can't get a decent direct line of sight,
then try the repeater.

(So much for keeping it simple...)

Jeff Liebermann <je***@comix.santa-cruz.ca.us> wrote:

Is this with one of the aftermarket firmware sets?  Or a minimum level of
Linksys standard firmware?

The basic WAP54G users guide doesn't mention WDS. 
Firmware 2.06 adds "repeater mode" which isn't in the online UG, even
though the UG is 6 months newer than 2.06 firmware.

Sniffing at linksysinfo.org is a tad confusing, since people speak so
freely of the Sveasoft firmware.  It's hard to tell what "stock" is.

The basic users guide indicates that "Access Point" and "Bridge Mode" are
mutually exclusive modes.

---
Clarence A Dold - Hidden Valley (Lake County) CA USA  38.8,-122.5

On Thu, 10 Mar 2005 02:34:29 +0000 (UTC),
d***@XReXXConne.usenet.us.com wrote:

Show quoteHide quoteArgh.  It's Sveasoft Freya v2.06-1sv for the WAP54G that adds WDS to
the WAP54G.  The current stock v2.08 firmware for the WAP54Gv2 doesn't
have WDS.  I think the other firmware releases (OpenWRT, HyperWAP,
MustDie, Neo, etc) also support WDS mode but I'm too lazy to check.
The big problem with the WAP54G is that it only has 2MBytes of flash
as compared to the WRT54G with 4MB and the GS with 8MB.  Kinda hard to
cram all that code in 2MBytes.

http://www.seattlewireless.net/index.cgi/WAP54G

If he uses the stock firmware, the only thing that will work for
bridging is to use two WAP54G boxes setup in transparent bridge mode
with CAT5 cables to each end.  Since the office end needs an access
point for it's local clients, these WAP54G bridge boxes would be in
addition to the existing WAP54G.  This could get messy and expensive.

No, repeater mode is mutually exclusive with access point mode.  I'm
not sure if it's mutually exclusive with client mode in the Sveasoft
Freya.

Yep.  Same problem in this newsgroups.  No manufacturer names, no
model numbers, no hardware revisions, no firmware revisions.  Sigh.  I
guess I complain to much and expect too much.

Yep.

One more correction.  My testing with using repeater mode between the
two antennas was done with a DWL-900AP+.  It's possible that the
repeater mode in the WAP54G has fixed the performance problem as it's
a completely different product.  I guess I should try it (later).

On Thu, 10 Mar 2005 02:34:29 +0000 (UTC),
d***@XReXXConne.usenet.us.com wrote:

Show quoteHide quoteFirmware is showing as 2.08

I find the documentation unhelpful.

I can only choose ONE of the following four modes:

Access point (default)
AP Client
Wireless Repeater
Wireless Bridge

The last 3 require a MAC address.

There is a note on the selection screen:

Note: When set to "AP Client" and "Wireless Bridge" mode, this device
will only communicate with another Linksys Access Point (WAP54G). When
set to "Wireless Repeater" mode, this device will only communicate
with another  Linksys Access Point (WAP54G) and Linksys Wireless-G
Router (WRT54G).

Tony Lewis <intothe***@hotmail.com> wrote:

Linksys, not third party, so the mode that Jeff referred to is unavailable.

Each of these requires the MAC address of the Access Point/Bridge that you
want to connect to.  That is to be expected.
I think repeater and bridge also require the partner to have your MAC
address entered in its table, but that isn't clearly documented.

I wonder about the "client" statement.  That should not be true.  A client
should be a standardized operation.

A repeater or bridge might operate in Linksys proprietary fashion.

On Wed, 09 Mar 2005 09:03:12 -0800, Jeff Liebermann <je***@comix.santa-cruz.ca.us> wrote:

That should be metres of course. Silly error.


  What type of coax?  I like numbers, not
Show quoteHide quoteBarry

On Tue, 08 Mar 2005 09:58:32 -0800, Jeff Liebermann
<je***@comix.santa-cruz.ca.us> wrote:

I've gathered some further information though I still haven't had time
to make alterations.

However somewhat lost in the threads is that the system is (just)
usable if I'm only using the Linksys in the window at the home end and
becomes unusable when I connect that end to the cantenna.

Further information below.

A few minutes at most.

Not yet - high on list of things to try as possible interference from
another wifi system on same channel has been identified.

Next thing to try after channel change.

Using  HDF200 cable - http://www.solwise.co.uk/wireless-cable.htm with
..5db loss/metre.  3metres at near end, 5 metres far end.

My colleague says he has measured and estimates 12dBi.   

Show quoteHide quoteI get 15.3 using my slightly more optimistic figures with one cantenna
and 25.8 using both. 

Show quoteHide quoteI can't get better line of sight than I have short of moving someone's
house!

Thanks for this. 

Will do and report.

Will do and report
..
I don't fully understand the term OFDM.  I have the following advanced
settings available:

Authentication Type            (Default: Auto)        
Transmission Rates            (Default: Auto)        
CTS Protection Mode            (Default: Disable)        
Basic Rates                (Default: Default)        
Antenna Selection            (Default: Diversity)

Frame Burst                (Default: off)        
Beacon Interval                (Default: 100,        
                Milliseconds,Range:20~1000 )

RTS Threshold                (Default: 2346, Range: 256 - 2346)

Fragmentation Threshold        (Default: 2346, Range: 256 - 2346)

DTIM Interval                (Default: 3, Range: 1 - 255)

I've set the transmission rates to the lowest (1mbps)

Is there a simple chart showing the maximum reliable speed for a given
theoretical operating margin (sorry if I've misused the terminology).
I will be satisfied with solid broadband performance (512k) over the
wireless link so 11mbps is in itself not essential. 

I assume that WEP is not a significant factor in all of this.

Many thanks

On Mon, 14 Mar 2005 11:25:06 GMT, intothe***@hotmail.com (Tony Lewis)
wrote:

Bottom line, you need either a clear path or LOTS more antenna gain.

"At most"?  Does that mean that it also occurs more frequently than a
"few" minutes?  Let me try a different approach.  Wireless traffic
tends to be erratic.  Click the mouse on a wireless web connection and
you get a burst of traffic.  Therefore, if you get dropouts at about
15-30 second intervals, followed by long pauses where they read the
mail or web page, it's interference.  Microwave oven interference
follows the TV dinner pattern.  It mostly happens around meal times
and tends to be 3-6 minutes of continuous outage with long intervals
in between where traffic is normal.  Cafeterias are different in that
they run almost continuously during meal times.  Cordless phones tend
to cause a total loss of signal for rather long periods (10-30 mins).
Do any of these fit your pattern?

Same as LMR200.  Including connectors with no pigtail, I would guess
2.5dB loss at one end, and 3.5dB at the other.

I beg to differ.  See:
9.8dB gain assuming everything is perfect.  I've only measured one can
antenna using the above dimensions and measured 7.8dB gain on channel
6 and about 6.5dB gain on channel 1 and 11.  That's using a conical
feed element instead of just a 1/4 wave wire, which has better
bandwidth (less VSWR).  It is possible to build a 12dBi coffee can
antenna, but it will be more like a horn antenna.  My guess is an
aperature diameter of no less than 250mm will yield about 12dB gain.
So, what type of coffee can are you using?

Way too optimistic for a coffee can antenna gain.  Revised numbers
including corrected coax cables and the slowest possible speed:
  TX power =  +15dBm   (Cantenna end)
  TX coax loss = 2.5dBm
  TX antenna gain = +8dBi
  Distance = 400 meters (0.25 miles)
  RX antenna gain = 0dBi
  RX coax loss = 3.5dBm
  RX sensitivity = -93dBm  (1Mbits/sec)
  Desired fade margin = ????

Now, I get 17.8dB which methinks is barely adequate.  If you hang a
can antenna on the other end, you'll pickup a huge 8dB increase and
this thing will work.  However, not that I'm using receive sensitivity
at the slowest speed.  If you crank up the speed somewhat
(recommended), then you'll loose some sensitivity.

Then, add about 10-20dB of loss into your fade margin calculations.
This isn't going to work unless you get line of sight or crank up the
power dramatically.

Won't work.  I goofed.  I thought you had two WAP54G radios.  Bridge
mode only works between matching pairs of wireless (transparent)
bridge radios.

Orthogonal Frequency Division Multiplexing.  Think of it as a
modulation method.  The 802.11g box supports several others.  I
usually tag my connection speeds with the modulation method.  Not an
issue.

The settings look just fine.

That will get you the most receiver sensitivity but not necessarily
the best thruput or most reliable connection.  I suggest you try
6Mbits/sec OFDM, which is the slowest OFDM, because OFDM deals with
reflections (off your intervening building) much better than CCK etc.

Actually yes.  I can create a simple table if I knew the exact chipset
demodulator characteristics and level of reliability (99.999%) you
were expecting.  Actually, I have one for older Orinoco Silver hanging
on the wall in front of me.  It's in the form of S/N ratio (Eb/No)
versus BER (bit error rate).  It's going to be tricky for marginal
links because the BER curve jumps abruptly as soon as the demodulator
starts working properly and chewing on data instead of noise.

WEP is good for about a 10% performance hit.

Bigger antennas.  Think dish or panel.

On Mon, 14 Mar 2005 23:23:24 GMT, Jeff Liebermann
<je***@comix.santa-cruz.ca.us> wrote:

That still doesn't account for it being tolerably usable with the
Linksys WAP54G in the Window and intolerable (see next para) when I
connect that Linksys to the cantenna.  Even using your figures below I
should be picking up 5.5dBi

Without the cantenna and with speed limited to 1mbps the throughput is
fairly consistent.  Adding the cantenna it freezes to a standstill.
When I first tested the cantenna (before fastening it to the wall -
just holding it towards the office cantenna) and settings at 11mpbs I
got 4mpbs for  short time then it dropped to  nothing.  Now whatever I
force the speed setting to it runs for a few minutes then drops to
nothing.

Reverting back to the rubber duck aerials and I'm running again.

I thought maybe the reason was that the higher gain cantenna might
have been picking up the other distant wifi system.  However changing
the channel to 1 hasn't helped.

As above, just a few minutes then hang (cantenna).

Show quoteHide quoteNo and none of these delays with the Linksys in the window.

There is just the one cable from each Linksys to the cantenna, so just
one extra connection at the cantenna (the linksys already has/had one
connection to the rubber duck aerial).

I looked at these earlier but it is not clear what I'm looking at.  Is
there a drawing of this cantenna design somewhere?

My colleague built it and I should have measured it before putting it
up :)   Approx 10" long and 4" diam to a design off the web.  Added a
conical horn to the home end so flares to about 8" diam in an attempt
to improve its performance.

I think I'm going to have to wander around and take some measurements
with Netstumbler and post them somewhere.

Show quoteHide quoteThat's the problem.  It doesn't but it tolerably does without the
cantenna.

I infer that  20dB is minimum for good results.

Show quoteHide quoteI **do** have WAP54G at both ends.   I'm bringing both Linksys
WAP54G's into the office, set to Bridge and connect one end with an
ethernet cable to my spare D-Link DWL-700AP and the other WAP54G to a
hub on my network.  Though I must say that doing the 400m and back
dash to reset something that has hung is good for my health.

Noted.

Not simple then :) 

Don't mind trying this if I can rule out any fresnel effects killing
the system.  As mentioned earlier I have the only clear line of sight
path available without going ridiculously high but not the clear path
you would prefer I had.  Much further expense and it will be cheaper
to put in broadband at home and add a vpn (though I'd miss out on all
the fun eh?)

On Tue, 15 Mar 2005 12:58:10 GMT, intothe***@hotmail.com (Tony Lewis)
wrote:

Nope.  There are too many assumptions.  You haven't tested the antenna
for gain.  There's also the not so minor problem of the obstruction in
the line of sight.  I arbitrarily gave it a 10 to 20dB loss.  Either
extreme will create a useless path.

As for it working with an omni and not a coffee can antenna, that can
also mean that your not getting the signal through the line of sight.
Instead, it's bouncing off of something, and you're getting the
reflection.  If you had a really high gain antenna (i.e. 24dBi dish)
with a 5-7 degree beamwidth, you could play direction finder and see
where the signal is really coming from.  I've been supervised more
than I care to admit with such sneaky paths.

Either the can antenna has a problem, or your signal is not coming
from the line of sight.  Hard to tell from here.

That does happen, but changing channels should fix that (assuming it's
802.11b DSSS interference).  Not this time.

Unclear.  Never mind.  It's probably not interference.

Sure.  It's a model of Trevor Marshall's can antenna design.  Note the
gain plot on the above URL.  Some notes on the original design at the
bottom of:
  http://www.nec2.org/wlan.htm
100mm inside diameter, 185mm long.  Conical driven element.

This might help.
  http://www.turnpoint.net/wireless/cantennahowto.html

The flared horn antennas will have more gain than 8dBi.  There was a
web site with construction details, but I can't seem to find it.
  http://www.saunalahti.fi/elepal/antenna2.html
12dBi to 14dBi are possible.

Watch out for reflections off the ground and from nearby buildings.

Getting a signal and keeping it online are two different animals.  You
can acquire lock at 0dB fade margin.  You'll get a connection but not
much else.  Everything you do will reduce the fade margin.  Unexpected
losses, line of sight obstructions, and interference all tend to ruin
a nice neat fad margin calculation.

No.  20dB is a good target for a RELIABLE link that stays up fairly
well.  20dB is 99.0% reliability.  That means your link will be down
for 3.65 days per year.  You can run a link with much less fade
margin, but the reliability gets rapidly worse.  I use 20dB as a
target value and settle for slightly less.  You can sorta test the
link fade margin by adding fixed attenuators in line with the radios

Looks like a worthy test.  Methinks results will be similar to the
current situation.

Well, no.  It's not simple.  I'm not sure it's even useful.  However,
it can be done.  Broadcom is not too liberal with passing out their
data sheets.  That last time I needed one, I had to go through an
ordeal process and was asked to sign an NDA (non-disclosure agreement)
in order to get spec sheets and reference design info.  I have some
Broadcom data, but I think it's from before the WRT54G and WAP54G
vintage chips.

You can't.  Even with high power and big antennas, objects in the path
will create knife edged diffraction and block the signal. 

You're decision.  VPN over ADSL will run at the rate of the outgoing
speed.  That's anywhere between 128kbit/sec and 768Mbits/sec.  That's
better than a modem, but not as fast as a decent wireless link can
run.

Jeff Liebermann <je***@comix.santa-cruz.ca.us> wrote:
ooo, I like that one.  I used an Orinoco and a coffee can to locate some
unauthorized WAPs in the building.  At 10 feet, it's a pretty good pointer.
Down the hallway, around the corner, maybe not so good.

(Trying the John Navas method of checking signal strength and walking
around wasn't worth diddly.)

Also, a reminder about your earlier comments about the cans not being bore
sight aligned.  I haven't noticed with a normal cantenna, but with a USB
cantenna, and lacking a line of sight shot makes for a best signal that
doesn't point the barrel of the can toward the wap.

My first thought was that his cantenna was less than good in its
construction.  A test with some nearby WAP might be in order.
For signal testing, the target WAP could be moved to someplace else.  It
shouldn't require a WAN connection to get a good wireless link for test
purposes.

Cantenna instructions:
http://www.turnpoint.net/wireless/cantennahowto.html
With the hood scoop:
<http://www.nodomainname.co.uk/Antennas/antenna.htm#Can%20with%20conical%20horn>
(David Taylor doesn't speak up much any more.)

Or maybe
<http://www.seattlewireless.net/index.cgi/DirectionalWaveguide>
and <http://www.seattlewireless.net/index.cgi/CookieCantenna>

---
Clarence A Dold - Hidden Valley (Lake County) CA USA  38.8,-122.5

On Wed, 16 Mar 2005 02:24:04 +0000 (UTC),
d***@XReXXConne.usenet.us.com wrote:

You can get easily fooled by reflections.  If the antenna has side
lobes (as is very common with a yagi), it's even more difficult to
play direction finder.  What I find works is a bit crude.  It's a
rotating antenna designed for minimum side lobes.  The antenna isn't
anything wonderful at approx 6dBi gain and a 40 degree -3dB beamwidth.
When spinning around, the detected signal and rotation are
synchronized to display on an oscilloscope.  You can see the signal
direction by a solid peak on the scope.  Reflections are very fuzzy
and are easily recognized, while the direct signal is generally quite
steady.

Before anyone suggest using doppler, please read these articles I
scribbled many years ago on the subject:
  http://www.qsl.net/n9zia/doppler_notes2.txt
  http://www.qsl.net/n9zia/doppler_notes1.txt
Note that this is 1970's technology.

That works if you use your body to block the signal.  Hold the USB
radio near your chest and spin around.  Look for a null.  When you
find it, the signal is coming from behind you.

Note the pattern at:
which shows about a 4 degree boresight error on a typical coffee can
antenna.  It's not much, but it's there.

This is a more sane and reasonable horn antenna.  16dBi gain with
built in stub tuner (for minimum vswr).
  http://www.g0mrf.freeserve.co.uk/horn.htm

Jeff Liebermann <je***@comix.santa-cruz.ca.us> wrote:
I've heard you say "spin" before.  I thought you meant turn, like I do with
my camera-tripod mounted coffee can.  I lost my oscilloscope somewhere.
Last I recall, I lent it to someone to hook up to speakers at a party.

There's that spin word again...  presumably at a different speed.  Looking
for the null was not something that I tried.  A USB dongle in my shirt
pocket might be effective.  I tried walking around with a laptop and a
WG511.  One open Linksys WAP was available everywhere, with signal provided
via bounce, and stronger at almost every hallway intersection.  A slow spin
looking for high signal wasn't helpful.  The Orinoco with a chili can was
directional enough, again looking for high signal, not low.  I needed a
cohort though.  He looked where the can was pointing, while I concentrated
on the screen.

I don't see the feed, or the spacing for it.  I presume it's coming in
through the coffee cup.  The waveguide dimensions are only 2 dimensional.
Where are the measurements for the horn?  The dimensions are discovered
from a program on a web site with no link.  It would have been so easy to
put in http://www.qsl.net/n1bwt/contents.htm but that reference material
looks more useful than this page.

http://seattlewireless.net/index.cgi/CardboardHorn has more information.
It also references the the Micro-Aerial, which is a handier size, and used
as the feed for the big horn on the page.  It even includes the picture
that you referenced, and the link to the qsl site.

This qsl.net book offers 31 pages of coffee can thoughts, including adding
a collar.  In the grand scheme of cobbling, it looks like a four inch
coffee can with a wood stove 4"-6" adapter added near the open end.  That
results in a big improvement in front to back ratio.  It is more compact
than a horn, and might be sufficient for my current project.

I don't see any "gain" expressed in the qsl charts.  On your coffee can
chart, it looks like the gain is discovered elsewhere, and just noted on
the chart, with the chart graphic being dB down from that known amount.

On Wed, 16 Mar 2005 17:53:47 +0000 (UTC),
d***@XReXXConne.usenet.us.com wrote:

Nope.  It's a motorized rotating antenna.  It's usually mounted on an
antenna mast with tripod in the back of my pickup truck, or in various
mutations that vary with size of the antenna and frequency.  I used it
for ham radio transmitter hunts and such, but haven't done much with
it for many years.  If you have a perfect signal source, no
reflections, and no VSWR, rotating the antenna will display the exact
antenna pattern on the oscilloscope screen.  It's almost like radar.
It works best when moving as the real signal shows up as a steady lobe
on the pattern, while the reflections come and go at random.  I
intentionally did not describe my 2.4Ghz version because it's not
finished, what I have doesn't work quite right, and I have illusions
of selling it as a product.  That will bring a new dimension to war
driving.

Ballet experience is helpful.  Actually, it's a common technique also
used in ham radio transmitter hunts.  Some of the local experts are
amazing.  Some wrap their radios in aluminium foil, exposing only a
small part of the antenna, to reduce the sensitivity when close.  Lots
of other tricks.  The problem with doing it using an 802.11b/g system
is that the signal strength meter is often slothish and insufficiently
granular.  There is software that will give a much better RSSI
reading, with good response time.  Netstumbler will also do it if you
increase the polling rate.  The Lucent client manager also works well.

Well, it should work, but I've never tried it with a USB dongle.  In a
hallway, you will have many reflections which will probably obscure
the direct signal.  It works outdoors, but I've never tried it
indoors.  I don't think it will work.

Yes, in the coffee cup.  It's described at the bottom of the page.
SMA connector with 4mm of brass rod.  A simple 1/4 wave feed.  The
coax is apparently not attached.


It's apparently not a construction article.  I could grind out the
numbers for the horn if you'd like.  I just wanted to illustrate what
a properly designed horn antenna looks like and how big a 16dBi gain
horn would really look like.  Basically, the horn aperature width
controls the gain.  The transition angle controls the bandwidth
(smoother transitions or tapered horns have a wider bandwidth).  The
stub tuning screws tune for minimum VSWR.  For ham radio satellite
work, the bandwidth required is very small.  Therefore, a rather
abrupt transition angle will work just fine.  For 802.11 bandwidths,
the horn will be much longer.

Yep.  Note that the W1GHZ waveguide feed articles are primarily
intended to illuminate a dish antenna.

This can get messy fast.  Basically, the gain of both the horn and the
coffee can is mostly (not totally) dependent upon the aperature
diameter.  Equal size "mouths" of these antennas should have roughly
equal amounts of gain.  However, the horn has a much neater coax
transition while the coffee can of equal diameter would spray RF all
over the place from wall reflections.

Incidentally, selection of materials is important.  The only reason
the coffee can works is that the surface is tin coated.  Skin effect
causes all the RF to stay on the surface of the coffee can.  Tin is
non-magnetic so it's a tolerable RF conductor.  However, a stove pipe
is a different story.  It's usually painted, not plated.  The RF
conducting surface is yucky magnetic steel, which is not so good a
conductor.  I'm amazed that it works at all.  One of my friends was
making 150Mhz cavity resonators out of stove pipe and found the skin
effect losses to be substantial.

Gain is the sum of many factors and is difficult to generalize for a
type of antenna.  In this case, the coffee can waveguide feeds were
designed to illuminate a dish antenna.  The gain of the entire system
is calculated (err... computed) in detail as a system, not just the
feed.  The gain provided by the dish part is usually much more than
that of the feed horn.  Therefore, small errors in the feed can be
ignored as the overall gain is set almost entirely by the dish
diameter.  In other words, the gain of the coffee can is not an
important consideration.  It has a big effect on overall dish
efficiency (overspray, under-illumination, vswr), but that is part of
the dish gain, not the feed.

On Tue, 15 Mar 2005 23:53:17 GMT, Jeff Liebermann
<je***@comix.santa-cruz.ca.us> wrote:

Not sure if I now understand netstumbler or if it gives truthfull
figures.  Siting the laptop about 2m from each of the linksys with
both of their rubber duck aerials connected gave me approx Signal -35
Noise -94.

I then connect a linksys to the cantenna, go outside and the reading
from about 6m below and 6m back (ie about 45deg and 8.5m away) is
Signal -50 Noise - 90.  I was expecting an improvement on the Signal.

Nonetheless:

This seems to have worked.  When all rigged up in the office and
setting the linksys (now bridges) to your recommendation of 6mbps I
get a throughput of around 1.5mpbs. 

When setup as finally required the throughput is around 1mbps and
fairly steady.  My firewall displays traffic flow rates and was
showing anywhere from 90kbytes/sec to 140kbytes/sec with very few if
any dropouts.   This is a big result and the first time I have had any
consistency of throughput with the cantennas talking to eachother.

I also seem to get a better signal from the D-link to the laptops at
home.

Once I'm satisfied that things are settled (and after I've got some
work I'm supposed to be doing out of the way) I want to see if there
is any more to squeeze out of the system.   This includes:

i) upping the speed of the linksys bridges from 6mbps
ii) setting the antenna from diversity to the one the cantenna is
connected to
iii) do I need WEP on the the linksys's or is it ignored anyway?  I
don't want to be double WEPing (ie D-Link is encrypting then the
bridge is encrypting again).
iv) The D-link has a rate setting called Basic (set to 2mpbs) and
another setting called Tx (set to 11mpbs).  Might change the Basic if
I can find out what it means.

My friendly farmer has cut his tree back for me (a few days ago so it
wasn't the reason for the improvement).   He hasn't offered to move
his house though :(

Don't know what conclusions can be drawn.  My uneducated guess is that
the home linksys was struggling to know which signals to adjust to
(notebooks in the house on one antenna and the cantenna on the other).

Our location is such that ADSL has only just arrived and will be
limited to 512k because of the distance from the exchange so the
throughput is not going to be limited by the wireless.

I use VNC to drive one of the work computers from home so there is not
much load there and then the occasional file transfer so I'm now
reasonably satisfied.

Thanks for your input and any further comments/observations will be
read with interest.

On Thu, 17 Mar 2005 12:06:41 GMT, intothe***@hotmail.com (Tony Lewis)
wrote:

Ignore the noise numbers.  Going from -35dBm signal to -50dBm is a
15dB *LOSS*.  Your can antenna has a problem.

If you set the bridges to a fixed connection rate of about 6mbits/sec,
you should get a TCP thruput of between 2 to 3mbits/sec.  With the two
radios next to each other, you'll probably get close to 3Mbit/sec.
Since you're getting 1.5mbits/sec, my guess(tm) is that you're getting
about 30% packet loss or resends due to interference and a lousy path
with probable reflections.  I still predict that if you can get this
link to work, it won't stay up and be reliable.

6Mbits/sec is the slowest OFDM rate.  Since I guess(tm) that you have
some reflections, going slower will only make it worse because CCK is
far worse at dealing with reflections than OFDM.  Since I also guess
that you currently are running with a 30% packet loss, any increase in
connection speed will just make that worse.  It makes no sense to
deliver corrupted packets at higher speeds.

That will help reduce local interference.

You should use WEP as someone could hijack the connection.  The only
other security is the pre-set MAC address of each end of the link,
which is easily spoofed.  Also, not enabling WEP will allow someone to
sniff the traffic.

Basic is compatibility with the older 802.11 only (1 and 2 Mbit/sec)
radios.  It also includes an ultra long preamble and other such
airtime burners.  Since you're NOT concerned with these or even
802.11b radios, it doesn't matter.  Once you set the data rate to a
fixed speed, all these setting become meaningless.  Set it for 802.11g
only so that it doesn't send management junk at 1Mbit/sec (another
airtime burner).

Put a repeater on the roof of his house.  Line-o-sight in both
directions.  If you make it solar powered, then you won't need any
wires going into the house.  I have a few of these in the tree tops.

That's my job.  You just present the evidence and numbers.

Yep. 

802.11g can go for miles with proper antennas (and line of sight).
How far do you have to shoot before you get to a house with faster
ADSL?

VNC requires good response time to be used effectively.  Check your
end to end ping times.  Packet loss will cause the ping time to
dramatically increase.  I use fping, which unlike Windoze ping, shows
the sequence numbers so you can see the packet loss.
  http://www.kwakkelflap.com/fping.html

Get a real or better antenna.  Netstumbler already proved that the can
antenna seems to be giving a -15dB loss.  Trust your measurments and
verify the with/without cantenna test using a more controlled location
or known good antenna.  I'm fairly sure you'll need some decent
antenna gain at each end to make this work.

Jeff Liebermann <je***@comix.santa-cruz.ca.us> wrote:
He was going outside, so the loss might be loss.  We didn't get to see the
outside naked number, but I agree.  I think his cantenna isn't as good as a
piece of coax, stipped back and folded over.


---
Clarence A Dold - Hidden Valley (Lake County) CA USA  38.8,-122.5

On Thu, 17 Mar 2005 09:43:02 -0800, Jeff Liebermann
<je***@comix.santa-cruz.ca.us> wrote:

Now I'm beginning to wonder if there is a problem with one or both of
the Linksys. 

My setting up of the bridge was all in one room, linksys's in bridge
mode next to eachother using all rubber ducks, the d-link about 3
metres away and me and my laptop offset in the middle.

I simply copied a 3Mb file from a Win98 PC on the 10mbit network to my
XP laptop taking around 20secs (for reference it takes 5.5 secs when
the XP is wired into the network).

The implication is that one(?) of the linksys's at least is reducing
the throughput then?

Tony Lewis <intothe***@hotmail.com> wrote:
Two possibilities:
When checking antennas using NetStumbler, I found I had to get some
distance in order to get good numbers.  Antennas show more obvious
improvement at fringe ranges.

I would go to the farthest range where the naked card can see the WAP,
and then connect the cantenna to see if there is an improvement.

Your cantenna is no good.  Bad cable, bad solder, bad location of the
probe, something.

---
Clarence A Dold - Hidden Valley (Lake County) CA USA  38.8,-122.5

On Thu, 17 Mar 2005 18:06:53 +0000 (UTC),
d***@XReXXConne.usenet.us.com wrote:

Show quoteHide quoteWish I measured both cantennas before sticking them up high.  Can't
get any further back from the office before I run into the office
behind (with the flat roof over which I have a couple of metres
clearance).  I can try the home one though.  

I'll have to borrow a forklift or cherry picker and go into the field
in the middle.

On Mon, 07 Mar 2005 14:20:52 GMT, intothe***@hotmail.com (Tony Lewis)
wrote:

Here you say 400 meters.

Here, I add 300m and 380m and get 680meters.  Is it 400m or 680m?

On Tue, 08 Mar 2005 10:31:51 -0800, Jeff Liebermann
<je***@comix.santa-cruz.ca.us> wrote:

Show quoteHide quotethe distances are absolute from Home.  400m total.  All the potential
obstructions are around the office end.

Building To Building
Wireless-wired-wireless re-radiator
belkin pre-n report
Problems with a Netgear wireless router
Bridge different subnets
Motorola WR850G as Access Point (not router)
Re: Wireless access point problems...
WiFi Bridge
Low or no signal in same room?
Intel Pro and SMC router