Vendor Radio Specs Untrustworthy

From a reliable source I am told that the various companies specs on the
power or range of various radios cannot be trusted.

Trouble is in weeks of searching various wifi questions I have found no
objective tests of various client mode radios.

Anyone know of any published tests where the vendor is not doing the
testing? Or even a company that publishes tests on it's products? I know
of one vendor that does, however he does not include most of the
products he sells and the tests are pretty vague.

JayJay wrote:
> From a reliable source I am told that the various companies specs on the
> power or range of various radios cannot be trusted.
>
> Trouble is in weeks of searching various wifi questions I have found no
> objective tests of various client mode radios.
>
> Anyone know of any published tests where the vendor is not doing the
> testing? Or even a company that publishes tests on it's products? I know
> of one vendor that does, however he does not include most of the
> products he sells and the tests are pretty vague.

If there is a way to force the wifi card to put our a constant carrier,
measuring the power output isn't all that difficult. Measuring
sensitivity is something else, though I suppose you could insert an
attenuator berween two cards wired with coax to measure sensitivity,
once you know the power output of the reference card.

I think I have enough gear to do the power measurement, but I don't own
any attenuators rated at 2.5GHz.

JayJay <(E-Mail Removed)> hath wroth:

>From a reliable source I am told that the various companies specs on the
>power or range of various radios cannot be trusted.

That's correct. Everybody lies, but that's ok because nobody listens.

>Trouble is in weeks of searching various wifi questions I have found no
>objective tests of various client mode radios.

I presume you've found some subjective tests. Any particular
measurements you're trying to determine?

>Anyone know of any published tests where the vendor is not doing the
>testing?

Yes. The problem is that I signed an NDA that limits what I can
disclose.

>Or even a company that publishes tests on it's products? I know
>of one vendor that does, however he does not include most of the
>products he sells and the tests are pretty vague.

If you go through the FCC type certification test reports, you'll see
page and after page of xmit power tests and measurement methods. Start
at:
http://www.fcc.gov/oet/fccid/
and search for whatever product you find interesting. The test report
is quite detailed. If you need test limits and general proceedures,
there's quite a bit in FCC Part 15 rules-n-regs.

Incidentally, many people measure xmit power with a spectrum analyzer
and wonder why they're yielding far too low in power output. The
problem is that the spectrum analyzer shows the direct sequence spread
spectrum signal splattered over a 22MHz bandwidth. In order for the
spectrum analyzer to measure the de-spread xmit power, you need to add
a correction for the spreading. For example, if the main lobe is
10Mhz wide, and the IF bandwidth of the SA is 1 MHz wide, you add:
10 log (10 / 1) = 10 log 10 = 10dB
So if the spectrum analyzer reads 5dBm xmit power, then the real CW
power is 10 + 5 = 15dBm.

Receiver sensitivity is a different mess. The problem is that there's
no FCC specification so EVERYONE lies (and I do mean everyone). Some
vendors use the chipset vendors sensitivity specs. Others
conveniently forget to include the coax cable pigtail loss, the
diversity switch loss, the matching network loss, the long trace
across the circuit board loss, etc. In almost all routers I've played
with, the sensitivity on each of the diversity antenna ports are
different.

Measuring receiver sensitivity is actually fairly easy if you happen
to have a BER (bit error rate) tester, a large bank accounty, and all
day to run the test. You setup the generator (about $18,000 hardware
plus $3,000 in software), connect to the access point ($50), and
connect a 100mbit/sec BER to the ethernet port ($8,000). Set the
access point to a fixed wireless speed. Increase the signal level
until the BER = 10E-5 (one error in every 100,000 bits). That's the
sensitivity. You can also measure PER (packet error rate) which is
quite a bit easier on the test equipment budget. Repeat the test for
each of the dozen speeds and modulation modes. Figure on about 15
minutes per speed to get a stable value.

Range is yet another mess. The problem is that speed, range, and
reliability are all interchangeable. I can go as far as you want, but
the link is not going to be very fast or very reliable. There are
estimators available that do a credible job of predicting the range
given the antennas, coax loses, path loss, Fresnel zone attentuation,
and of course equipment used. That's the ideal and everything else
reduces the range from the ideal. For example, rain, inversion
layers, interference, corrosion, moisture, bird shit, coax adapters,
and rotten coax will all reduce the range.

There are plenty of path and link calculators online. See the FAQ at:
http://wireless.wikia.com/wiki/Wi-Fi#Link_Calculations
for how to do a simple link calculation. You might also be interested
in the theoretical maximum speeds at:
http://wireless.wikia.com/wiki/Wi-Fi...ance_and_Speed

So, what problem are you trying to solve?

--
Jeff Liebermann (E-Mail Removed)
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:
> JayJay <(E-Mail Removed)> hath wroth:
>
> >From a reliable source I am told that the various companies specs on the
> >power or range of various radios cannot be trusted.
>
> That's correct. Everybody lies, but that's ok because nobody listens.
>
> >Trouble is in weeks of searching various wifi questions I have found no
> >objective tests of various client mode radios.
>
> I presume you've found some subjective tests. Any particular
> measurements you're trying to determine?
>
> >Anyone know of any published tests where the vendor is not doing the
> >testing?
>
> Yes. The problem is that I signed an NDA that limits what I can
> disclose.
>
> >Or even a company that publishes tests on it's products? I know
> >of one vendor that does, however he does not include most of the
> >products he sells and the tests are pretty vague.
>
> If you go through the FCC type certification test reports, you'll see
> page and after page of xmit power tests and measurement methods. Start
> at:
> http://www.fcc.gov/oet/fccid/
> and search for whatever product you find interesting. The test report
> is quite detailed. If you need test limits and general proceedures,
> there's quite a bit in FCC Part 15 rules-n-regs.
>
> Incidentally, many people measure xmit power with a spectrum analyzer
> and wonder why they're yielding far too low in power output. The
> problem is that the spectrum analyzer shows the direct sequence spread
> spectrum signal splattered over a 22MHz bandwidth. In order for the
> spectrum analyzer to measure the de-spread xmit power, you need to add
> a correction for the spreading. For example, if the main lobe is
> 10Mhz wide, and the IF bandwidth of the SA is 1 MHz wide, you add:
> 10 log (10 / 1) = 10 log 10 = 10dB
> So if the spectrum analyzer reads 5dBm xmit power, then the real CW
> power is 10 + 5 = 15dBm.

Some gear has a button to compute the power in a band as all the
information is present in the analyser. In fact, this feature is
present in some audio gear as well since telecom works in power rather
than peak to peak voltage.
>
> Receiver sensitivity is a different mess. The problem is that there's
> no FCC specification so EVERYONE lies (and I do mean everyone). Some
> vendors use the chipset vendors sensitivity specs. Others
> conveniently forget to include the coax cable pigtail loss, the
> diversity switch loss, the matching network loss, the long trace
> across the circuit board loss, etc. In almost all routers I've played
> with, the sensitivity on each of the diversity antenna ports are
> different.
>
> Measuring receiver sensitivity is actually fairly easy if you happen
> to have a BER (bit error rate) tester, a large bank accounty, and all
> day to run the test. You setup the generator (about $18,000 hardware
> plus $3,000 in software), connect to the access point ($50), and
> connect a 100mbit/sec BER to the ethernet port ($8,000). Set the
> access point to a fixed wireless speed. Increase the signal level
> until the BER = 10E-5 (one error in every 100,000 bits). That's the
> sensitivity. You can also measure PER (packet error rate) which is
> quite a bit easier on the test equipment budget. Repeat the test for
> each of the dozen speeds and modulation modes. Figure on about 15
> minutes per speed to get a stable value.
>
> Range is yet another mess. The problem is that speed, range, and
> reliability are all interchangeable. I can go as far as you want, but
> the link is not going to be very fast or very reliable. There are
> estimators available that do a credible job of predicting the range
> given the antennas, coax loses, path loss, Fresnel zone attentuation,
> and of course equipment used. That's the ideal and everything else
> reduces the range from the ideal. For example, rain, inversion
> layers, interference, corrosion, moisture, bird shit, coax adapters,
> and rotten coax will all reduce the range.
>
> There are plenty of path and link calculators online. See the FAQ at:
> http://wireless.wikia.com/wiki/Wi-Fi#Link_Calculations
> for how to do a simple link calculation. You might also be interested
> in the theoretical maximum speeds at:
> http://wireless.wikia.com/wiki/Wi-Fi...ance_and_Speed
>
> So, what problem are you trying to solve?
>
> --
> Jeff Liebermann (E-Mail Removed)
> 150 Felker St #D http://www.LearnByDestroying.com
> Santa Cruz CA 95060 http://802.11junk.com
> Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann <(E-Mail Removed)> wrote in
news(E-Mail Removed):

> JayJay <(E-Mail Removed)> hath wroth:
>
>>From a reliable source I am told that the various companies specs on
the
>>power or range of various radios cannot be trusted.
>
> That's correct. Everybody lies, but that's ok because nobody listens.

Be nice to know what a product is capable of BEFORE you buy it.

>
>>Trouble is in weeks of searching various wifi questions I have found
no
>>objective tests of various client mode radios.
>
> I presume you've found some subjective tests. Any particular
> measurements you're trying to determine?

Already said: transmit power and receive sensitivity

>
>>Anyone know of any published tests where the vendor is not doing the
>>testing?
>
> Yes. The problem is that I signed an NDA that limits what I can
> disclose.
>
>>Or even a company that publishes tests on it's products? I know
>>of one vendor that does, however he does not include most of the
>>products he sells and the tests are pretty vague.
>
> If you go through the FCC type certification test reports, you'll see
> page and after page of xmit power tests and measurement methods. Start
> at:
> http://www.fcc.gov/oet/fccid/
> and search for whatever product you find interesting. The test report
> is quite detailed. If you need test limits and general proceedures,
> there's quite a bit in FCC Part 15 rules-n-regs.

Are you referring to:
https://gullfoss2.fcc.gov/prod/oet/c...ericSearch.cfm ?
If so, then you have to get alot of other info to fill in all the blanks
first.

> There are plenty of path and link calculators online. See the FAQ at:
> http://wireless.wikia.com/wiki/Wi-Fi#Link_Calculations
> for how to do a simple link calculation. You might also be interested
> in the theoretical maximum speeds at:
> http://wireless.wikia.com/wiki/Wi-Fi...ance_and_Speed

To use these reliably you still need ACCURATE power and receive figures,
or else garbage in garbage out.

>
> So, what problem are you trying to solve?

To know what a product is capable of BEFORE buying. Example there are at
least 3 "high power" pcmcia cards out there with similar claims in their
data sheets. Which is telling the truth and how to compare? Ditto,
outdoor units.

JayJay <(E-Mail Removed)> hath wroth:

>> http://www.fcc.gov/oet/fccid/

>Are you referring to:
>https://gullfoss2.fcc.gov/prod/oet/c...ericSearch.cfm ?
>If so, then you have to get alot of other info to fill in all the blanks
>first.

All you need is the FCC ID number on the serial number sticker.
You can also use the vendor search to get the 3 letter FCC ID prefixes
used by the vendor, and then just browse through their list of
hardware. The FCC ID search does sorta work, but not consistently or
reliably. Pick a maker and model number and I'll demonstrate how it
works.

>> There are plenty of path and link calculators online. See the FAQ at:
>> http://wireless.wikia.com/wiki/Wi-Fi#Link_Calculations
>> for how to do a simple link calculation. You might also be interested
>> in the theoretical maximum speeds at:
>> http://wireless.wikia.com/wiki/Wi-Fi...ance_and_Speed

>To use these reliably you still need ACCURATE power and receive figures,
>or else garbage in garbage out.

True. It really depends on what level of accuracy you're trying to
achieve. 1dB is about 9% accuracy. Since the range calculations are
based on a rather wide fade margin of 20dB, the results are at best a
ballpark guess. That's the nature of the beast for range calculations
as there is no abrupt transition between good/bad for range. There
are also a mess of minor variables that will add additional errors. It
makes no sense to nail the power and sensitivity to within perhaps 1dB
and then use these to guess the range with perhaps a 10dB variation in
fade margin plus another 10dB in minor path impediments.

Incidentally, when I was measuring receiver sensitivity on the bench
with big bux test equipment, I would frequently get 3dB variations in
results just before lunch and after lunch. Some of these variations
were obvious, but most of them were untraceable. In other words,
accurate numbers are difficult to get.

Also, one fun exercise was to have everyone in the lab read the
indicated power of a spread spectrum signal on a spectrum analyzer.
Without touching anything, 5 different people gave 5 different results
varying over about a 3dB range.

>> So, what problem are you trying to solve?
>
>To know what a product is capable of BEFORE buying. Example there are at
>least 3 "high power" pcmcia cards out there with similar claims in their
>data sheets. Which is telling the truth and how to compare? Ditto,
>outdoor units.

I'm with you there. The recent trend in data sheet product is to
supply the absolute minimum amount of information possible. The
reason is that users tend to sue if they don't get the advertised
features or preformance. I too would like to see detailed
specifications, especially receiver dynamic range, but that's not what
sells commodity hardware. You'll get that on high end radios (Proxim,
Alvarion, and Aironet/Cisco, but not on cheap junk.

If I could give you accurate numbers that I personally tested, how
could you be sure I'm trustworthy? Would you settle for a range of
numbers? If so, I'll give you 3 sigma variations, which accounts for
98% of the units shipped, but is such a wide range that the numbers
would be useless.

--
Jeff Liebermann (E-Mail Removed)
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:
> JayJay <(E-Mail Removed)> hath wroth:
>
> >> http://www.fcc.gov/oet/fccid/
>
> >Are you referring to:
> >https://gullfoss2.fcc.gov/prod/oet/c...ericSearch.cfm ?
> >If so, then you have to get alot of other info to fill in all the blanks
> >first.
>
> All you need is the FCC ID number on the serial number sticker.
> You can also use the vendor search to get the 3 letter FCC ID prefixes
> used by the vendor, and then just browse through their list of
> hardware. The FCC ID search does sorta work, but not consistently or
> reliably. Pick a maker and model number and I'll demonstrate how it
> works.
>
> >> There are plenty of path and link calculators online. See the FAQ at:
> >> http://wireless.wikia.com/wiki/Wi-Fi#Link_Calculations
> >> for how to do a simple link calculation. You might also be interested
> >> in the theoretical maximum speeds at:
> >> http://wireless.wikia.com/wiki/Wi-Fi...ance_and_Speed
>
> >To use these reliably you still need ACCURATE power and receive figures,
> >or else garbage in garbage out.
>
> True. It really depends on what level of accuracy you're trying to
> achieve. 1dB is about 9% accuracy. Since the range calculations are
> based on a rather wide fade margin of 20dB, the results are at best a
> ballpark guess. That's the nature of the beast for range calculations
> as there is no abrupt transition between good/bad for range. There
> are also a mess of minor variables that will add additional errors. It
> makes no sense to nail the power and sensitivity to within perhaps 1dB
> and then use these to guess the range with perhaps a 10dB variation in
> fade margin plus another 10dB in minor path impediments.
>
> Incidentally, when I was measuring receiver sensitivity on the bench
> with big bux test equipment, I would frequently get 3dB variations in
> results just before lunch and after lunch. Some of these variations
> were obvious, but most of them were untraceable. In other words,
> accurate numbers are difficult to get.

Does the test equipment have a "referece" transmitter, or do you test
two wifi boxes as WAP and client, checking BERT vs signal level. If it
is the later, then there is the situation where you are doing BERT with
your box talking to your box, then your box talking to another box,
etc.

>
> Also, one fun exercise was to have everyone in the lab read the
> indicated power of a spread spectrum signal on a spectrum analyzer.
> Without touching anything, 5 different people gave 5 different results
> varying over about a 3dB range.

Why not use a power meter?
>
> >> So, what problem are you trying to solve?
> >
> >To know what a product is capable of BEFORE buying. Example there are at
> >least 3 "high power" pcmcia cards out there with similar claims in their
> >data sheets. Which is telling the truth and how to compare? Ditto,
> >outdoor units.
>
> I'm with you there. The recent trend in data sheet product is to
> supply the absolute minimum amount of information possible. The
> reason is that users tend to sue if they don't get the advertised
> features or preformance. I too would like to see detailed
> specifications, especially receiver dynamic range, but that's not what
> sells commodity hardware. You'll get that on high end radios (Proxim,
> Alvarion, and Aironet/Cisco, but not on cheap junk.

Technically, what a chip manufacturer insures with a datasheet is that
if you find the part does not meet the specifications, they will refund
your purchase or give you a new chip. Now the parts are factory tested,
but the consumer grade chips may only get one test (probably hot). The
manufacturer tries to infer from one test that the part will work over
temperature and power supply range.

By test, I mean a suite of tests on ATE Most manufacturers will list
their test flow in the catalog/website. The flow could be 100% hot and
QA cold (test a small subset), or GBD (Guaranteed By Design) for
temperature. Having designed chips for GDB, I personally don't have a
lot of faith in it. However, market forces lead to such testing in
consumer products. Generally there is a footnote and some verbage like
"Guaranteed by design. Not subject to production testing", "Guaranteed
by design, characterization or correlation to other tested
parameters.", etc.

>
> If I could give you accurate numbers that I personally tested, how
> could you be sure I'm trustworthy? Would you settle for a range of
> numbers? If so, I'll give you 3 sigma variations, which accounts for
> 98% of the units shipped, but is such a wide range that the numbers
> would be useless.
>
> --
> Jeff Liebermann (E-Mail Removed)
> 150 Felker St #D http://www.LearnByDestroying.com
> Santa Cruz CA 95060 http://802.11junk.com
> Skype: JeffLiebermann AE6KS 831-336-2558

(E-Mail Removed) hath wroth:

>Does the test equipment have a "referece" transmitter, or do you test
>two wifi boxes as WAP and client, checking BERT vs signal level.

The signal generator section has an 802.11b "transmitter". Actually,
it's a fairly generic QAM modulator, with overpriced software 802.11
emulation.

>If it
>is the later, then there is the situation where you are doing BERT with
>your box talking to your box, then your box talking to another box,
>etc.

The BER does talk to itself. However, there's no loop as the pseudo
random data generator is independent of the data receiver. It has to
be in the same box because there's no other way to detect any errors
without known what was sent.

The output of the BER random data generator goes to a different piece
of equipment that acts as a BER tester. The BER sends data to the
signal generator. The modulator does the QAM thing. The RF
oscillator acts as a transmitter. The access point receives the RF
through a coax cable. The output is ethernet, which goes to an
ethernet to serial converter, and then to the BER tester. The tester
compares the sent data, with the received data, and counts the number
of discrepancies (errors).

>> Also, one fun exercise was to have everyone in the lab read the
>> indicated power of a spread spectrum signal on a spectrum analyzer.
>> Without touching anything, 5 different people gave 5 different results
>> varying over about a 3dB range.
>
>Why not use a power meter?

Because I blew up the thermistor head for the HP 435A power meter. We
were trying to figure out if the spectrum analyzer was accurate enough
to substitute until the head came back from repair and calibration.

>Technically, what a chip manufacturer insures with a datasheet is that
>if you find the part does not meet the specifications, they will refund
>your purchase or give you a new chip.

It's difficult to separate failure to meet component specifications on
a production board. The RF chipset may be just fine, but digital
noise on the board could ruin the sensitivity. One reason that many
manufacturers use the chipset reference design and layout is so that
they can point the finger at the vendor if something doesn't work.

--
Jeff Liebermann (E-Mail Removed)
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:
> (E-Mail Removed) hath wroth:
>
> >Does the test equipment have a "referece" transmitter, or do you test
> >two wifi boxes as WAP and client, checking BERT vs signal level.
>
> The signal generator section has an 802.11b "transmitter". Actually,
> it's a fairly generic QAM modulator, with overpriced software 802.11
> emulation.
>
> >If it
> >is the later, then there is the situation where you are doing BERT with
> >your box talking to your box, then your box talking to another box,
> >etc.
>
> The BER does talk to itself. However, there's no loop as the pseudo
> random data generator is independent of the data receiver. It has to
> be in the same box because there's no other way to detect any errors
> without known what was sent.
>
> The output of the BER random data generator goes to a different piece
> of equipment that acts as a BER tester. The BER sends data to the
> signal generator. The modulator does the QAM thing. The RF
> oscillator acts as a transmitter. The access point receives the RF
> through a coax cable. The output is ethernet, which goes to an
> ethernet to serial converter, and then to the BER tester. The tester
> compares the sent data, with the received data, and counts the number
> of discrepancies (errors).
>
> >> Also, one fun exercise was to have everyone in the lab read the
> >> indicated power of a spread spectrum signal on a spectrum analyzer.
> >> Without touching anything, 5 different people gave 5 different results
> >> varying over about a 3dB range.
> >
> >Why not use a power meter?
>
> Because I blew up the thermistor head for the HP 435A power meter. We
> were trying to figure out if the spectrum analyzer was accurate enough
> to substitute until the head came back from repair and calibration.

Yeah, blowing up the sensor is a real life hazard. Any funny thing is,
nobody knows how it happened. I like, er, just went to use the power
meter and it didn't work. [The Tek current probe failure is another lab
mystery. Well, not really a mystery as if you drop it, it stops
working. Just noboy remembers dropping it.]

Technically, the HP meter is a bolometer. I'll admit I never saw the
word until I was reading the manual on a radio I acquired, which had a
spot to connect the bolometer.


>
> >Technically, what a chip manufacturer insures with a datasheet is that
> >if you find the part does not meet the specifications, they will refund
> >your purchase or give you a new chip.
>
> It's difficult to separate failure to meet component specifications on
> a production board. The RF chipset may be just fine, but digital
> noise on the board could ruin the sensitivity. One reason that many
> manufacturers use the chipset reference design and layout is so that
> they can point the finger at the vendor if something doesn't work.
>
> --
> Jeff Liebermann (E-Mail Removed)
> 150 Felker St #D http://www.LearnByDestroying.com
> Santa Cruz CA 95060 http://802.11junk.com
> Skype: JeffLiebermann AE6KS 831-336-2558

(E-Mail Removed) hath wroth:

>Yeah, blowing up the sensor is a real life hazard. Any funny thing is,
>nobody knows how it happened. I like, er, just went to use the power
>meter and it didn't work.

Nope. I know exactly who blew it up and how. It was me screwing
around with some ham radio equipment. For a 25 watt xmitter, I
usually use a -30dB 100watt load/attenuator between the xmitter and
the power meter. That will deliver +14dBm to the HP435A which is well
within its operating range. Unfortunately, the lab had a spare "dead"
attenuator that should have been either fixed or tossed long ago.
Although labeled -30dB, it's really more like -10dB. That will
deliver +34dBm (3 watts) to the thermistor, which will kill it. Since
the good attenuator was being used, I grabbed the wrong attenuator.
Don't ask what this cost me.

>[The Tek current probe failure is another lab
>mystery. Well, not really a mystery as if you drop it, it stops
>working. Just noboy remembers dropping it.]

Fingerprint the probe. If you're clever, you can tell the age of the
fingerprint and who handled it last.

Remember: Blame must be assigned before any problem can be solved.

>Technically, the HP meter is a bolometer. I'll admit I never saw the
>word until I was reading the manual on a radio I acquired, which had a
>spot to connect the bolometer.

Strictly speaking, a thermistor is a type of bolometer, which is the
general term for an EM energy sensor. For the HP meter head, either
is correct.

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