Jeff Liebermann wrote:

...
Maybe, but more likely, not enough RF to do anything useful with an
un-amplified meter.

What's missing from everyone's posting is what they plan to do with
this field strength meter.

Let's play with the numbers. The average wi-fi access point belches
about +12dBm (32 mw) RF into an antenna with perhaps 2dBi gain. The

Hmmm, max power for a wifi router is 1 watt!

Here is a full power one:

http://www.wirelessnetworkproducts.c...OD&ProdID=1425

The router I presently use is "belching" 500mw into a 7.5db antenna
(well, I might question the 7.5db ...)

Throw out your access point man! Get a decent one ...

Regards,
JS

On Mon, 08 Dec 2008 00:59:16 -0800, John Smith
wrote:

Jeff Liebermann wrote:

...
Maybe, but more likely, not enough RF to do anything useful with an
un-amplified meter.

What's missing from everyone's posting is what they plan to do with
this field strength meter.

Let's play with the numbers. The average wi-fi access point belches
about +12dBm (32 mw) RF into an antenna with perhaps 2dBi gain. The

Hmmm, max power for a wifi router is 1 watt!

I said "average wi-fi access point". 1 watt routers are relatively
rare among the common home wireless routers. Most run about 32mw.
Some Buffalo models run about 250mw. 2wire 2701 can run up to about
450mw. I think Enginius also makes one at around 1 watt.

The problem with this is what I call the "alligator" effect. An
alligator is an animal with a big mouth and small ears. Running a 1
watt access point will make the xmitter heard over a much wider area
than it can hear the responses from the clients. Unless the other end
of the link (i.e. client radios) are also running the same high power
level, the range will be limited by the clients tx power. In other
words, the system gain and power levels in both directions have to be
evenly matched to avoid turning the high power access point into what
I consider to be no better than a jamming transmitter. If you need a
slogan, you should use "only as much power as necessary" which doesn't
mean crank it up to the max. Please print this slogan on a large sign
and plaster it in front of your desk until the meaning sinks in. Also,
note that most modern communications technologies includes automatic
transmit power control (usually based on RX SNR or BER) to prevent
alligators and systems like yours from becoming a problem.

Here is a full power one:
http://www.wirelessnetworkproducts.c...OD&ProdID=1425
The router I presently use is "belching" 500mw into a 7.5db antenna
(well, I might question the 7.5db ...)

Turn down the power to about 100mw. The antenna is fine because it
results in a symmetrical improvement in system gain. Also, give
yourself a slap on the wrist, repent your evil ways, and pray for
forgiveness.

Throw out your access point man! Get a decent one ...

You haven't seen my office. I never throw anything away.

Regards,
JS
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:

...
Turn down the power to about 100mw. The antenna is fine because it
results in a symmetrical improvement in system gain. Also, give
yourself a slap on the wrist, repent your evil ways, and pray for
forgiveness.

Throw out your access point man! Get a decent one ...

You haven't seen my office. I never throw anything away.

Regards,
JS

Yes, my AP's software allows for power control. Indeed, the AP will,
automatically, only supply enough power to make a, almost, error free
transmission link.

Having one side of transmission link error free is MUCH superior to have
both sides error prone!

However, although I have a pocketfull of various USB dongles, my
external USB wifi "card" is the highest output I could find which is
cost effective (@ 500mw.) External USB being powered off the USB buss
must stay 500ma (@ 5v) or below, total consumption. And, would more
than allow for a 1 watt USB dongle.

Here is a USB card to match my router:

http://www.data-alliance.net/servlet...802.11n/Detail

Try one, you'll like it, "Mikey does!" grin

Regards,
JS

On Mon, 08 Dec 2008 01:51:53 -0800, John Smith
wrote:

Jeff Liebermann wrote:

...
Turn down the power to about 100mw. The antenna is fine because it
results in a symmetrical improvement in system gain. Also, give
yourself a slap on the wrist, repent your evil ways, and pray for
forgiveness.

Throw out your access point man! Get a decent one ...

You haven't seen my office. I never throw anything away.

Regards,
JS

Yes, my AP's software allows for power control. Indeed, the AP will,
automatically, only supply enough power to make a, almost, error free
transmission link.

I beg to differ. Unless I missed something in my post-midnight scan
of the specs, the wireless router's TX power is set and forget. If it
receives an extremely strong signal level report in the 802.11
management packet, the power remains the same. The ability to do
power control is there (because each device reports its RX signal
strength and SNR) but very few access points even try.

Having one side of transmission link error free is MUCH superior to have
both sides error prone!

I beg to differ. You're creating un-necessary interference. Let's
play with the numbers.

The commodity wireless router belches about +12dBm. Yours is
allegedly +27dBm. Range doubles for every 6dB increase in TX power.
Therefore, your TX range is:
(27 - 12) / 6 = 7.5
time more than would be with a commodity wireless router. In terms of
coverage area, that's:
7.5^2 = 56.3
times the area. Assuming a uniform density of WLAN users in your
vicinity, you're trashing 56.3 times as many users or systems as
necessary.

You're also partly wrong about asymmetrical systems being superior.
The transition between a fairly good BER or PER (packet error rate) is
rather abrupt. What happens is that the AP simply slows down the data
rate until the PER improves. Since the connection speed can be
different in each direction, you'll get very good speed in one
direction, and probably very slow speed in the other. In addition,
things go insane above 54Mbits/sec connection speed. You might have
enough signal to go faster than 54Mbits/sec in one direction, but if
it's lacking in the other direction, the AP will simply revert to
802.11g and limit the speed in the stronger direction to 54Mbits/sec.
That's not a problem as few systems can operate reliably at
54Mbits/sec beyond a few meters range and in the presence of
interference.

Meanwhile, you're operating an alligator, jamming 56 times as many
users as necessary, and polluting the airwaves with your overpowered
xmitter. It's like operating a kilowatt xmitter in the middle of the
QRP frequencies. Your stuff gets through, but nobody else's. I
suggest you do the math, repent your evil ways, offer sacrifice to the
radio gods on the hibachi, slap yourself on the wrist several times
for penitence, and stop playing with the dark side.

However, although I have a pocketfull of various USB dongles, my
external USB wifi "card" is the highest output I could find which is
cost effective (@ 500mw.) External USB being powered off the USB buss
must stay 500ma (@ 5v) or below, total consumption. And, would more
than allow for a 1 watt USB dongle.

You would do better with a directional antenna, so as to not both
pickup and deliver interference from other systems. Antennas with
gain also improve the system gain in both directions, thus preventing
the creation of an alligator.

Here is a USB card to match my router:
http://www.data-alliance.net/servlet...802.11n/Detail

Try one, you'll like it, "Mikey does!" grin

Nope. Instead, I was instrumental in convincing at least one mesh
wi-fi vendor to reduce their poletop TX power, as they were causing
most of their own interference. Asymmetric systems suck.

Regards,
JS

Bah-Humbug (T'is the season).

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:


I beg to differ. Unless I missed something in my post-midnight scan
of the specs, the wireless router's TX power is set and forget. If it
receives an extremely strong signal level report in the 802.11
management packet, the power remains the same. The ability to do
power control is there (because each device reports its RX signal
strength and SNR) but very few access points even try.


You are speaking of the specs on the USB card, I am speaking access
point ... and actually, I have never searched for power-throttling in
the USB card, I simply would not use it ... when the wife and I go out
and I search for APs, I want every possible mw in action, at a clients,
hotel, hospital, etc.

Having one side of transmission link error free is MUCH superior to have
both sides error prone!

I beg to differ. You're creating un-necessary interference. Let's
play with the numbers.


Let's not, I said what I meant, and meant what I said, one side error
free is better than two sides error prone.

The commodity wireless router belches about +12dBm. Yours is
allegedly +27dBm. Range doubles for every 6dB increase in TX power.
Therefore, your TX range is:
(27 - 12) / 6 = 7.5
time more than would be with a commodity wireless router. In terms of
coverage area, that's:
7.5^2 = 56.3
times the area. Assuming a uniform density of WLAN users in your
vicinity, you're trashing 56.3 times as many users or systems as
necessary.


No problem. I don't live in a dorm, trailer park, high-rise or
apartment building ... the software will automatically adjust to find
the best chan and recheck this decision, from time-to-time. If others
don't have that capability, they may wish to upgrade ... like I have
strongly implied, already, "If your AP is crap, toss it out!" I can't
imagine anyone here who failed to read specs before purchasing, however ???

You're also partly wrong about asymmetrical systems being superior.
The transition between a fairly good BER or PER (packet error rate) is
rather abrupt. What happens is that the AP simply slows down the data
rate until the PER improves. Since the connection speed can be
different in each direction, you'll get very good speed in one
direction, and probably very slow speed in the other. In addition,
things go insane above 54Mbits/sec connection speed. You might have
enough signal to go faster than 54Mbits/sec in one direction, but if
it's lacking in the other direction, the AP will simply revert to
802.11g and limit the speed in the stronger direction to 54Mbits/sec.
That's not a problem as few systems can operate reliably at
54Mbits/sec beyond a few meters range and in the presence of
interference.


The equip can do b/g/n (b&g for the usb card in question, multiple
computers here) With a windows widget to monitor my ap/card connection
(transfer rate, errors, signal strength, etc.), I see it rise and fall
from time to time. Sometimes I have seen the connection renegotiate
from n to g to b ... however, at this same time AirSnare has went nuts.
Seems wardriving teens are to blame ... grin I was a teen once, so
long ago, I fear I may forget ... :-(

But, I will tell you, if ever I notice a problem with the errors (just
looked, 3 errors), I will remember your words.

Meanwhile, you're operating an alligator, jamming 56 times as many
users as necessary, and polluting the airwaves with your overpowered
xmitter. It's like operating a kilowatt xmitter in the middle of the
QRP frequencies. Your stuff gets through, but nobody else's. I
suggest you do the math, repent your evil ways, offer sacrifice to the
radio gods on the hibachi, slap yourself on the wrist several times
for penitence, and stop playing with the dark side.


Although, I am sure one or two of my neighbors are savvy enough to set
their routers into non-broadcast mode of the SSID, and have WPA and
filter on mac addresses, I just don't see the traffic/jam you speak of.
But, like I say, if I do, I shall remember your words.

However, although I have a pocketfull of various USB dongles, my
external USB wifi "card" is the highest output I could find which is
cost effective (@ 500mw.) External USB being powered off the USB buss
must stay 500ma (@ 5v) or below, total consumption. And, would more
than allow for a 1 watt USB dongle.

You would do better with a directional antenna, so as to not both
pickup and deliver interference from other systems. Antennas with
gain also improve the system gain in both directions, thus preventing
the creation of an alligator.


No, I would NOT. When I take my laptop and USB antenna analyzer out to
the antenna(s), I appreciate my omni. When I take my laptop and USB ODB
II out to the car (in another direction), I appreciate my omni. When
teens go by wardriving and trigger AirSnare warnings (and giving me
one-hell-of-a-kick!), I appreciate my omni. You hang around with the
old men here, beware the cynicism, it IS contagious!

Here is a USB card to match my router:
http://www.data-alliance.net/servlet...802.11n/Detail

Try one, you'll like it, "Mikey does!" grin

Nope. Instead, I was instrumental in convincing at least one mesh
wi-fi vendor to reduce their poletop TX power, as they were causing
most of their own interference. Asymmetric systems suck.


Beware. Again you risk being controlled by the control freaks here.
Glad it works for you, attempt to enforce it for me, we have a battle
.... you know, there is equip and hacks available to open up chans far in
excess of what is legal, I am sure some are savvy and use them ...
perhaps teenagers? straight face I have even heard of some flashing
their ap/cards with the foreign version of the software for them and
exceeding power/chans ... shame on them! :-|

Regards,
JS

Bah-Humbug (T'is the season).


However, you provide good discussion, and have valid arguments, I am
sure--some will agree with and appreciate--perhaps even some which are
state-of-the-art!

Personally, I would NEVER suggest purchasing an AP/card with less than
350mw capability. And, only then if you get one-hell-of-a-buy.

Warm regards,
JS

John Smith wrote:

...
Personally, I would NEVER suggest purchasing an AP/card with less than
350mw capability. And, only then if you get one-hell-of-a-buy.

Warm regards,
JS


Sorry to have been so verbal. I could have summed that up rather
quickly, nicely and sweetly, I choose not to ...

You see millions of cell phones; You see a LOT of problems?

Regards,
JS

On Mon, 08 Dec 2008 11:35:12 -0800, John Smith
wrote:

You see millions of cell phones; You see a LOT of problems?

Oh yes, I certainly do see problems. They're well hidden and
mitigated in various ways. For example, if the error rate climbs, the
adaptive tx power control cranks up the power on both the handset and
the cell site end. If it persists, you get disconnected. Rather than
have the user sound like they're talking while gargling ball bearings,
the cell site just pulls the plug. Incidentally, the tx power control
algorithm is rather messy as it has to handle different data types, at
different rates, all while doing its best not to drain the handset
battery. One the cell site end, it's no better as the power
consumption of a typical cell site is non-trivial.

Problems? Well:
http://www.roughlydrafted.com/2008/08/28/the-inside-deets-on-iphone-202-and-dropped-calls/
Hmmm... power control algorithm again.

Todays typical cell phones run about 150mw max average power output
(according to the FCC ID data). Some are even less. None are
anywhere near the 600mw legal maximum. If they could, you would have
a dead battery within about an hour. (Do the math).

Back to wi-fi and your setup. Sure, you'll have fairly good
preformance with a high power setup. 14 times the usual power is
bound to do some good. However, I suspect your neighbors are not so
thrilled and will probably also be shopping for higher power hardware.
It will be like an arms race, where the biggest bomb allegedly wins.
Dealing with mutual interference is no fun, especially with only 3
available non-overlapping channels.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

In article ,

The problem with this is what I call the "alligator" effect. An
alligator is an animal with a big mouth and small ears. Running a 1
watt access point will make the xmitter heard over a much wider area
than it can hear the responses from the clients. Unless the other end
of the link (i.e. client radios) are also running the same high power
level, the range will be limited by the clients tx power. In other
words, the system gain and power levels in both directions have to be
evenly matched to avoid turning the high power access point into what
I consider to be no better than a jamming transmitter.

A not-uncommon scenario, I think. I've seen APs which put out a
signal that has useful strength for blocks, and yet you have to be
within about 100 feet of them to establish contact with a typical
client system.

This same issue is significant in other bands, as well. My area's
ham-radio VHF/UHF repeater coordination group has a firm principle...
a coordinated repeater's transmit coverage and receive coverage should
be consistent. Having an ultra-high-powered transmitter simply causes
interference well outside the repeater's practical use range.

Having overly-sensitive receivers can also be a problem, albeit a
lesser one, as it means that the repeater can be "keyed up" by remote
stations too far away to hear the repeater properly. It's less of
a problem, though, as most repeaters use CTCSS tone squelch these days
and won't respond to signals intended for co-channel repeaters with a
different CTCSS tone. I don't think this is an issue for 802.11
access points at all.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On Mon, 8 Dec 2008 11:17:10 -0800, (Dave Platt)
wrote:

A not-uncommon scenario, I think. I've seen APs which put out a
signal that has useful strength for blocks, and yet you have to be
within about 100 feet of them to establish contact with a typical
client system.

About a year ago, I was trying to find the source of a very strong
2.4GHz signal in the downtown Santa Cruz mall area. Wi-Fi
communications among the various coffee shops and hot spots was
ummm.... a challenge. I eventually traced it down to a tall
residential hotel and a 2.4GHz cordless digital phone running what I
guess was a 10 watt power amplifier. Instead of a cell phone, this
person decided to provide his own cordless phone service that covered
the entire downtown area. You could see it anywhere but as is
predictable, his useful range was limited by the handset power, which
was well less than 10 watts. I'm not going to go into detail on
exactly what happened, but it should be sufficient that he's now aware
of the problem he was causing and is off the air.

Be the first in your neighborhood to dominate the airwaves:
http://www.ssbusa.com/kunamp1.html
Cool... 50 watt linear on 2.4GHz. Now, we're cooking.

This same issue is significant in other bands, as well. My area's
ham-radio VHF/UHF repeater coordination group has a firm principle...
a coordinated repeater's transmit coverage and receive coverage should
be consistent. Having an ultra-high-powered transmitter simply causes
interference well outside the repeater's practical use range.

Good plan but there are problems. Most hams these daze use walkie
talkies with perhaps 1 watt of TX RF. The typical repeater is running
perhaps 10 to 40 watts out (after the duplexer). The walkie can hear
the repeater almost anywhere, but when trying to talk, they drop in
and out all the time. The mobiles, which run more power, are usually
well matched to the repeater's tx power. I've suggested adaptive tx
power control (to preserve battery power) on our 2 meter repeater, but
nobody wants it.

Having overly-sensitive receivers can also be a problem, albeit a
lesser one, as it means that the repeater can be "keyed up" by remote
stations too far away to hear the repeater properly. It's less of
a problem, though, as most repeaters use CTCSS tone squelch these days
and won't respond to signals intended for co-channel repeaters with a
different CTCSS tone.

We had a co-channel user that was running carrier squelch. It took
only about 7 years of constantly pounding on the trustees before they
would install PL. They lied on their NARCC application claiming they
had a functional PL system. The experience taught me a few things,
one of which is that hams generally make lousy RF neighbors.

I don't think this is an issue for 802.11
access points at all.

No, it's not for most home systems. There's a similar coexistence
problem with mesh networks and municipal networks. Neither of these
scale very well. They work ok with a small number of repeaters, but
rapidly foul up as the usage, traffic, and number of repeaters
increases to the point of mutual interference. Details and a rant on
request.

There's also a problem with wi-fi and omnidirectional antennas. These
pickup and spew inference from all direction equally well. Same with
reflections and multi-path. If the main area of operation can better
be covered with a directional antenna, then it should be used. It may
create hidden nodes, but those can be handled by enabling flow
control.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

In article ,
Jeff Liebermann wrote:

Good plan but there are problems. Most hams these daze use walkie
talkies with perhaps 1 watt of TX RF. The typical repeater is running
perhaps 10 to 40 watts out (after the duplexer). The walkie can hear
the repeater almost anywhere, but when trying to talk, they drop in
and out all the time. The mobiles, which run more power, are usually
well matched to the repeater's tx power. I've suggested adaptive tx
power control (to preserve battery power) on our 2 meter repeater, but
nobody wants it.

Seems to me that would introduce another set of incompatibilities.
People out on the fringe area of the repeater's coverage would be able
to hear repeated signals from weak transmitters (e.g. HTs), but if the
repeater saw a strong input signal from a mobile (or an HT near the
site) and dropped its transmitter power, the repeater coverage area
would shrink abruptly and those users out around the edges could lose
coverage. This could re-create the "hidden node" problem in a new way!

I don't think adaptive power management can work reliably in the
absense of a signal-quality feedback from each station which is
accessing the repeater/AP.

We had a co-channel user that was running carrier squelch. It took
only about 7 years of constantly pounding on the trustees before they
would install PL. They lied on their NARCC application claiming they
had a functional PL system.

Grrr. Worf "Romulans have *no* sense of honor." /Worf

Our system (W6ASH, SPECS, at El Camino Hospital in Mountain View)
switched over to PL-tone-only years ago, and it helps in numerous
ways... the absence of noise-initiated kerchunking is a real blessing.
I've preserved the ability to switch the repeaters over to
carrier-sense-only in an emergency but really don't expect to ever
need to use this feature.

The experience taught me a few things,
one of which is that hams generally make lousy RF neighbors.

Some are lousy neighbors, lazy and self-centered. Others hold
themselves and their equipment and operation to very high standards. I
think it depends very much on the individuals involved, on their
attitudes, and on their level of prior experience in supporting a
real-world user community.

No, it's not for most home systems. There's a similar coexistence
problem with mesh networks and municipal networks. Neither of these
scale very well. They work ok with a small number of repeaters, but
rapidly foul up as the usage, traffic, and number of repeaters
increases to the point of mutual interference. Details and a rant on
request.

I believe you!

My impression is that a limited set of mesh repeaters, and a plentiful
set of direct backhaul links on a different (non-interfering) band,
works out rather better.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!