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

http://www.n6mrx.com/Antenna/Cubical-Quad1.htm

Thanks for the link. The calculator works for me.

One remaining Q: how do I take into account the "pigtails" of the driven
element? A nice square loop is nice, but I've got to connect it to the
(relatively) big diode, and this requires a bit more wire from the loop to
the diode (on the + side of the loop) and to the meter connector (on the -
side). Do I include these wire lengths in the loop size calculation? Or
ignore them?

Or does the 1000pF cap effectively terminate the loop (re. size)?

Thanks.

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

On Mon, 8 Dec 2008 08:24:55 -0800, SparkyGuy
wrote:

Q: how do I take into account the "pigtails" of the driven
element? A nice square loop is nice, but I've got to connect it to the
(relatively) big diode,

You don't need to include diode lead length in the quad antenna
calculations. The "loop" in the quad driven element is just an LC
tuned circuit. It's as bit less than one wavelength around the loop
and resonated to 2.4GHz by the tuning cap. The diode and other
components do add some capacitance, which will lower the frequency
somewhat, but the adjustment cap is substantially larger than these
capacitances. For example, the off capacitance of a Schottky diode is
about 0.5pf. You do need to keep lead length short as the added
inductance will act as an RF choke.

However, instead of the giant diode, I suggest something smaller and
better, such as a Schottky diode:
http://www.adsemi.com/diodes/schottky_barrier_mixer_detector.shtml
http://www.macom.com/psc/jsp/ListParts.jsp?dataFile=mixing_detector_diodes.txt

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

You don't need to include diode lead length in the quad antenna
calculations.

Thanks, Jeff. Very much appreciated.

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!

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