In message .net,
SparkyGuy writes
It's probably not actually all that important.
dplatt

- - -

Thanks for your comments and evaluation of the project. They are helpful to
someone not skilled in the black art of wireless :-)

I plan to modify the design a bit, eliminating all coax connectors &
adapters, using just 2 banana plugs (and supporting plastic block) as the
connection to the meter.

Is it any more efficient to use copper foil or PCB material as the reflector
rather than wire?

Thanks.


A novel bit of kit, looking at the photos it appears to be being used
with a DVM, depending on how you want to use it you may find an analogue
meter easier. It will show changes better than a DVM. How about buying
a movement and a box and building a totally dedicated unit? I'm tempted
to make something similar.
--
Bill
May God defend me from my friends; I can defend myself against my enemies.

Bill wrote:
looking at the photos it appears to be being used
with a DVM, depending on how you want to use it you may find an analogue
meter easier. It will show changes better than a DVM.

The author says he tried that and it didn't work as well:
"I tried connecting the antenna directly to a micro amp moving
coil meter, however there was very little meter deflection from
a Wireless LAN card."

Impedance too low, perhaps?

Clifford Heath.

On Mon, 08 Dec 2008 08:37:34 +1100, Clifford Heath
wrote:

Bill wrote:
looking at the photos it appears to be being used
with a DVM, depending on how you want to use it you may find an analogue
meter easier. It will show changes better than a DVM.

The author says he tried that and it didn't work as well:
"I tried connecting the antenna directly to a micro amp moving
coil meter, however there was very little meter deflection from
a Wireless LAN card."

Impedance too low, perhaps?

Clifford Heath.

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
FSM has a gain of perhaps 0dB. At a distance of about 3 meters (10ft)
the path loss at 2.4GHz is about 50dB which will deliver about -30dBm
to the diode. On the most sensitive voltage range, the DVM has an
input impedance of at least 1Mohm and can be treated like an open
circuit load to the detector.

-30dBm into 50 ohms is 0.224 vrms. Transforming linearly from 50 ohm
reference to perhaps 150 ohms loop antenna impedance yields about
600mv rms. (Note: I know this is a bad guess but it's midnight and
I'm tired). Resonating the loop probably raises the impedance even
higher, thus resulting in even more rectified voltage.

The resultant DC voltage will be about the same at about 600mv DC.
However, for wi-fi use, the xmit duty cycle is quite low, sending just
beacons, when there is no traffic moving. The 1000pf cap will need to
be paralleled with a much larger cap in order to form a usable peak
detector.

So, with a high imput impedance DVM the antenna and detector is quite
efficient and can generate quite a bit of voltage. However, when the
DVM is replaced with a non-amplified meter, the relatively low
impedance of the meter shorts out the diode and signifigantly reduces
the Q of the resonant loop antenna, resulting in much lower detected
voltage.

I've built several transmitter hunt "sniffers" using almost exactly
the same circuit, except that I use a hot carrier Schottky diode for
the RF detector, and the cheapest Harbor Freight DVM (because it
always gets destroyed or lost during the hunt). For 2.4GHz, I use a
dish antenna, RF amplifier, step-up xformer (coax balun), diode
detector, and DVM.

I also made a really ugly hack that uses a satellite TV signal meter.
http://www.sadoun.com/Sat/Products/Accessories/Meters/SF95L-DSS-FTA-Satellite-Signal-meter.htm
These work from about 900 to 1800MHz with a minimum detectable meter
sensitivity of about -70dBm. They are comatose at 860 (cellular) and
2.4GHz but are great for 900 and 1900MHz (PCS) sniffing. The input
port is connected to a 900MHz or 1.2GHz antenna of any sorts. The
output goes to a 75 ohm load and a 12V battery (gel cell) through an
RF choke.

--
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:

...
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

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

Dave Platt wrote:
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.


All the problems you state would disappear with the correct algorithms
controlling the packets/encryption/compaction ... there is just not
enough interest to put together a team together to do it, and a
for-profit organization would go broke doing it ... and, you can't get
everyone to agree. The (A)ncient (R)etarded (R)adio (L)aggards) don't
see a need--you see, no brass is required ... :-(

Regards,
JS