krw@att.bizzzzzzzzzzzz wrote:> On Wed, 20 Oct 2010 09:57:14 +0200, Stef > <stef33d@yahooI-N-V-A-L-I-D.com.invalid> wrote: > >> In comp.arch.embedded, >> krw@att.bizzzzzzzzzzzz <krw@att.bizzzzzzzzzzzz> wrote: >>> On Tue, 19 Oct 2010 17:42:24 -0700, Joerg <invalid@invalid.invalid> wrote: >>> >>>> krw@att.bizzzzzzzzzzzz wrote: >>>>> On Tue, 19 Oct 2010 09:13:10 -0700, Joerg <invalid@invalid.invalid> wrote: >>>>> >>>>>> krw@att.bizzzzzzzzzzzz wrote: >>>>>>> On Mon, 18 Oct 2010 18:53:20 -0700, Joerg <invalid@invalid.invalid> wrote: >>>>>>> >>>>>>>> krw@att.bizzzzzzzzzzzz wrote: >>>>>>>>> On Mon, 18 Oct 2010 11:24:11 -0700, Joerg <invalid@invalid.invalid> wrote: >>>>>>>>> >>>>>>>>>> krw@att.bizzzzzzzzzzzz wrote: >>>>>>>>>>> On Sun, 17 Oct 2010 17:14:42 -0700, Joerg <invalid@invalid.invalid> wrote: >>>>>>>>>>> >>>>>>>>>>>> krw@att.bizzzzzzzzzzzz wrote: >>>> [...] >>>> >>>>>>>> This is because chamber measurements are not very precise. >>>>>>> Hmm. The chamber is the gold standard. A 3M isn't worth much, but we've had >>>>>>> no trouble with the 10M. The rotary table and all that jazz is in there. >>>>>>> >>>>>> That would be up to the EMC lab I guess. If they sign on the dotted line >>>>>> without open range measurements, well, dicey. The labs I went to never >>>>>> did that unless all the nasties were way under the limits. >>>>> They've never even suggested open range measurements. The company with the 3m >>>>> chamber couldn't get the same numbers twice, though. >> The company that does most of our testing does initial testing in the chamber >> and if everything is 10dB under the limits, they will pass the product. If >> there are higher peaks, but still under the limit, they will re-measure those >> at the OATS (Open Area Test Site). > > The two companies we've used rely on their chambers exclusively. Note that > one of them I don't trust - can't get the same answer twice. The other > calibrates all their chambers across the company periodically (better than > monthly). Neither has ever suggested OATS, even when we were on the cusp.Even when on the cusp? Yikes! That's playing with fire. [...] -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Wireless that's "Fall off a log" easy?
Started by ●October 11, 2010
Reply by ●October 20, 20102010-10-20
Reply by ●October 22, 20102010-10-22
On Wed, 20 Oct 2010 17:32:16 -0700, Joerg <invalid@invalid.invalid> wrote:>krw@att.bizzzzzzzzzzzz wrote: >> On Wed, 20 Oct 2010 11:32:00 -0700, Joerg <invalid@invalid.invalid> wrote: >> >>> krw@att.bizzzzzzzzzzzz wrote: >>>> On Tue, 19 Oct 2010 17:42:24 -0700, Joerg <invalid@invalid.invalid> wrote: >>>> >>>>> krw@att.bizzzzzzzzzzzz wrote: >>>>>> On Tue, 19 Oct 2010 09:13:10 -0700, Joerg <invalid@invalid.invalid> wrote: >>>>>> >>>>>>> krw@att.bizzzzzzzzzzzz wrote: >>>>>>>> On Mon, 18 Oct 2010 18:53:20 -0700, Joerg <invalid@invalid.invalid> wrote: >>>>>>>> >>>>>>>>> krw@att.bizzzzzzzzzzzz wrote: >>>>>>>>>> On Mon, 18 Oct 2010 11:24:11 -0700, Joerg <invalid@invalid.invalid> wrote: >>>>>>>>>> >>>>>>>>>>> krw@att.bizzzzzzzzzzzz wrote: >>>>>>>>>>>> On Sun, 17 Oct 2010 17:14:42 -0700, Joerg <invalid@invalid.invalid> wrote: >>>>>>>>>>>> >>>>>>>>>>>>> krw@att.bizzzzzzzzzzzz wrote: >>>>> [...] >>>>> >>>> ... I let the >>>> compliance lab worry about their chamber. That's what they get paid the big >>>> bux for. >>>> >>> Yup. And there one has to do everything to minimize those bux. Like not >>> doing de-facto pre-compliance runs there, which surprisingly many >>> companies end up doing. >> >> Turns out that our "pre-compliance" runs were worthless. The results couldn't >> be duplicated. >> > >Strange. They should have shown you the heavy hitters. Mine worked, >every single time.??? They did. Every time we went to scan the box the "heavy hitters" were different. The couldn't repeat the tests within 6dB, when their claimed margin of error was less than 3dB (2.2, IIRC). <snip>>> I had a little time today (emphasis on "little"): >> >> "15.215 Additional provisions to the general radiated >> emission limitations. >> >> (c) Intentional radiators operating under the alternative provisions >> to the general emission limits, as contained in ��15.217 through 15.257 >> and in Subpart E of this part, must be designed to ensure that the >> 20 dB bandwidth of the emission, ... > > >That's indeed remarkable. Seems you can let 20mW spill over past 902MHz >or 928MHz. But, reading on ... > >> ... or whatever bandwidth may otherwise >> be specified in the specific rule section under which the equipment >> operates, is contained within the frequency band designated in the >> rule section under which the equipment is operated. The requirement >> to contain the designated bandwidth of the emission within the specified >> frequency band includes the effects from frequency sweeping, frequency >> hopping and other modulation techniques that may be employed as well >> as the frequency stability of the transmitter over expected variations >> in temperature and supply voltage. If a frequency stability is not >> specified in the regulations, it is recommended that the fundamental >> emission be kept within at least the central 80% of the permitted band >> in order to minimize the possibility of out-of-band operation." >> >> Both test labs (the module manufacturer likes one, we prefer the other) >> interpret this the same way; that the intentional radiator has to be 20dB down >> outside its band. >> >> Now, this (prior) paragraph contradicts this... >> >> "(b) In most cases, unwanted emissions outside of the frequency bands >> shown in these alternative provisions must be attenuated to the >> emission limits shown in �15.209. ... > > >Aha! That means no free lunch after all.But how does this reconcile with the 20dB bandwidth, above? It's from the same paragraph. Transmitter can be 20dB down outside its band but still has to meet 11.209? Makes no sense.>> ... In no case shall the level of the >> unwanted emissions from an intentional radiator operating under these >> additional provisions exceed the field strength of the fundamental >> emission. >> >> ..except for the "most cases". The interpretation from both labs is that (c) >> overrules (b). Harmonics from the hopping are certainly above 12.209. >> > >It doesn't matter what the lab interprets. If the sheriff has this >brought to court and you lose, a major recall may follow because the >judge said so. Possibly wiping out the EMC lab and shaking up the place >where you work.I doubt the EMC lab is going down. It's a major corporation.>> Our box, without the radiator passes 12.209 (below for information) but the >> radio does not, outside its band. The radio has a separate cert. <scratches >> head> >> > >If the radio doesn't pass I'd be rather concerned.It doesn't. Interestingly, the 2.4G model does (but the harmonics are significant). I questioned it, but no one likes the bearer of bad news.>>>> ... The problem is that it takes a few more hours to >>>> guarantee that it meets the "no go zone" edges. ... >>> >>> Now wait, are you now saying there are areas where it must meet class B? >>> If so, that's what I was saying all along. >> >> In the restricted zones, yes. Outside of those zones it apparently does *NOT* >> have to meet class A/B. They looked at the spectrum and saw one place where >> we were close. They made sure that pup was outside the (frequency) window and >> all was goodness. It *was* over the Class-A line but would have passed (and >> actually did when the module had its cert done). >> > >Hopefully they are right ...Right about the interpretation? I'm not convinced either.>>> ... I stumbled onto this because >>>> the radio module does *not* meet the unintentional limits by itself. I turned >>>> it off and our box passes with 12dB to spare. If they can radiate like >>>> radium, why can't we? ;-) Seems all it takes is a redefinition of what the >>>> "intentional radiator" is. >>>> >>> Ok, intentional in the allowed band. I can't imagine they allow >>> excessive radiation _outside_ the permitted band. That would swing the >>> doors wide open to abuse. >> >> No, out-of-band must be 20dB below the in-band. ...didn't make any sense to >> me, either. > > >Way I read the law above it ain't so. Not across the whole frequency range.At what frequency then? The rule makes no sense.
Reply by ●October 22, 20102010-10-22
krw@att.bizzzzzzzzzzzz wrote:> On Wed, 20 Oct 2010 17:32:16 -0700, Joerg <invalid@invalid.invalid> wrote: > >> krw@att.bizzzzzzzzzzzz wrote: >>> On Wed, 20 Oct 2010 11:32:00 -0700, Joerg <invalid@invalid.invalid> wrote: >>> >>>> krw@att.bizzzzzzzzzzzz wrote:[...]>>>>> ... I let the >>>>> compliance lab worry about their chamber. That's what they get paid the big >>>>> bux for. >>>>> >>>> Yup. And there one has to do everything to minimize those bux. Like not >>>> doing de-facto pre-compliance runs there, which surprisingly many >>>> companies end up doing. >>> Turns out that our "pre-compliance" runs were worthless. The results couldn't >>> be duplicated. >>> >> Strange. They should have shown you the heavy hitters. Mine worked, >> every single time. > > ??? They did. Every time we went to scan the box the "heavy hitters" were > different. The couldn't repeat the tests within 6dB, when their claimed > margin of error was less than 3dB (2.2, IIRC). >At very high frequencies that could be almost normal. All it takes is a couple screws not being jammed in as they were last time. Other than that, old rule: Photograph the setup from multiple angles with a wooden yard stick on the table. Believe it or not, almost nobody does. Then, next times set it up _exactly_ as in that photo. Do not let wires droop over the saw horse any differently.> <snip> > >>> I had a little time today (emphasis on "little"): >>> >>> "15.215 Additional provisions to the general radiated >>> emission limitations. >>> >>> (c) Intentional radiators operating under the alternative provisions >>> to the general emission limits, as contained in ��15.217 through 15.257 >>> and in Subpart E of this part, must be designed to ensure that the >>> 20 dB bandwidth of the emission, ... >> >> That's indeed remarkable. Seems you can let 20mW spill over past 902MHz >> or 928MHz. But, reading on ... >> >>> ... or whatever bandwidth may otherwise >>> be specified in the specific rule section under which the equipment >>> operates, is contained within the frequency band designated in the >>> rule section under which the equipment is operated. The requirement >>> to contain the designated bandwidth of the emission within the specified >>> frequency band includes the effects from frequency sweeping, frequency >>> hopping and other modulation techniques that may be employed as well >>> as the frequency stability of the transmitter over expected variations >>> in temperature and supply voltage. If a frequency stability is not >>> specified in the regulations, it is recommended that the fundamental >>> emission be kept within at least the central 80% of the permitted band >>> in order to minimize the possibility of out-of-band operation." >>> >>> Both test labs (the module manufacturer likes one, we prefer the other) >>> interpret this the same way; that the intentional radiator has to be 20dB down >>> outside its band. >>> >>> Now, this (prior) paragraph contradicts this... >>> >>> "(b) In most cases, unwanted emissions outside of the frequency bands >>> shown in these alternative provisions must be attenuated to the >>> emission limits shown in �15.209. ... >> >> Aha! That means no free lunch after all. > > But how does this reconcile with the 20dB bandwidth, above? It's from the > same paragraph. Transmitter can be 20dB down outside its band but still has > to meet 11.209? Makes no sense. >That's one reason why I wouldn't gamble on it. Lots of rules don't make sense. But if anyone feels trampled upon such as the sheriff, he who has more muscle or deeper pockets wins. Taxpayer pockets are often deepest because it costs "nothing" :-(>>> ... In no case shall the level of the >>> unwanted emissions from an intentional radiator operating under these >>> additional provisions exceed the field strength of the fundamental >>> emission. >>> >>> ..except for the "most cases". The interpretation from both labs is that (c) >>> overrules (b). Harmonics from the hopping are certainly above 12.209. >>> >> It doesn't matter what the lab interprets. If the sheriff has this >> brought to court and you lose, a major recall may follow because the >> judge said so. Possibly wiping out the EMC lab and shaking up the place >> where you work. > > I doubt the EMC lab is going down. It's a major corporation. >Then they hopefully have good liability insurance, just in case. And your company might be more protected as long as this large EMC company blessed the gear.>>> Our box, without the radiator passes 12.209 (below for information) but the >>> radio does not, outside its band. The radio has a separate cert. <scratches >>> head> >>> >> If the radio doesn't pass I'd be rather concerned. > > It doesn't. Interestingly, the 2.4G model does (but the harmonics are > significant). I questioned it, but no one likes the bearer of bad news. >Ok, that's up to corporate mgmt I guess. In medical we take such things seriously because the next bearer of bad news might be cruising into the parking lot in a car with government plates. No joke, that happened to a large ultrasound company. I bet some bigshots stood there with egg in the face.>>>>> ... The problem is that it takes a few more hours to >>>>> guarantee that it meets the "no go zone" edges. ... >>>> Now wait, are you now saying there are areas where it must meet class B? >>>> If so, that's what I was saying all along. >>> In the restricted zones, yes. Outside of those zones it apparently does *NOT* >>> have to meet class A/B. They looked at the spectrum and saw one place where >>> we were close. They made sure that pup was outside the (frequency) window and >>> all was goodness. It *was* over the Class-A line but would have passed (and >>> actually did when the module had its cert done). >>> >> Hopefully they are right ... > > Right about the interpretation? I'm not convinced either. > >>>> ... I stumbled onto this because >>>>> the radio module does *not* meet the unintentional limits by itself. I turned >>>>> it off and our box passes with 12dB to spare. If they can radiate like >>>>> radium, why can't we? ;-) Seems all it takes is a redefinition of what the >>>>> "intentional radiator" is. >>>>> >>>> Ok, intentional in the allowed band. I can't imagine they allow >>>> excessive radiation _outside_ the permitted band. That would swing the >>>> doors wide open to abuse. >>> No, out-of-band must be 20dB below the in-band. ...didn't make any sense to >>> me, either. >> >> Way I read the law above it ain't so. Not across the whole frequency range. > > At what frequency then? The rule makes no sense.That's what I don't understand either. There may possibly be buffers between your band and any important stuff. But sometimes not. For example, there is no buffer between the DECT and the cell band. Your DECT spills over and the lawyers of some telco giant might be all over you. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Reply by ●October 22, 20102010-10-22
On Fri, 22 Oct 2010 17:05:39 -0700, Joerg <invalid@invalid.invalid> wrote:>krw@att.bizzzzzzzzzzzz wrote: >> On Wed, 20 Oct 2010 17:32:16 -0700, Joerg <invalid@invalid.invalid> wrote: >> >>> krw@att.bizzzzzzzzzzzz wrote: >>>> On Wed, 20 Oct 2010 11:32:00 -0700, Joerg <invalid@invalid.invalid> wrote: >>>> >>>>> krw@att.bizzzzzzzzzzzz wrote: > >[...] > >>>>>> ... I let the >>>>>> compliance lab worry about their chamber. That's what they get paid the big >>>>>> bux for. >>>>>> >>>>> Yup. And there one has to do everything to minimize those bux. Like not >>>>> doing de-facto pre-compliance runs there, which surprisingly many >>>>> companies end up doing. >>>> Turns out that our "pre-compliance" runs were worthless. The results couldn't >>>> be duplicated. >>>> >>> Strange. They should have shown you the heavy hitters. Mine worked, >>> every single time. >> >> ??? They did. Every time we went to scan the box the "heavy hitters" were >> different. The couldn't repeat the tests within 6dB, when their claimed >> margin of error was less than 3dB (2.2, IIRC). >> > >At very high frequencies that could be almost normal. All it takes is a >couple screws not being jammed in as they were last time. Other than >that, old rule: Photograph the setup from multiple angles with a wooden >yard stick on the table. Believe it or not, almost nobody does. Then, >next times set it up _exactly_ as in that photo. Do not let wires droop >over the saw horse any differently.30MHz and 230MHz are not amazingly high frequencies when the DSP is running at 100MHz.>> <snip> >> >>>> I had a little time today (emphasis on "little"): >>>> >>>> "15.215 Additional provisions to the general radiated >>>> emission limitations. >>>> >>>> (c) Intentional radiators operating under the alternative provisions >>>> to the general emission limits, as contained in ��15.217 through 15.257 >>>> and in Subpart E of this part, must be designed to ensure that the >>>> 20 dB bandwidth of the emission, ... >>> >>> That's indeed remarkable. Seems you can let 20mW spill over past 902MHz >>> or 928MHz. But, reading on ... >>> >>>> ... or whatever bandwidth may otherwise >>>> be specified in the specific rule section under which the equipment >>>> operates, is contained within the frequency band designated in the >>>> rule section under which the equipment is operated. The requirement >>>> to contain the designated bandwidth of the emission within the specified >>>> frequency band includes the effects from frequency sweeping, frequency >>>> hopping and other modulation techniques that may be employed as well >>>> as the frequency stability of the transmitter over expected variations >>>> in temperature and supply voltage. If a frequency stability is not >>>> specified in the regulations, it is recommended that the fundamental >>>> emission be kept within at least the central 80% of the permitted band >>>> in order to minimize the possibility of out-of-band operation." >>>> >>>> Both test labs (the module manufacturer likes one, we prefer the other) >>>> interpret this the same way; that the intentional radiator has to be 20dB down >>>> outside its band. >>>> >>>> Now, this (prior) paragraph contradicts this... >>>> >>>> "(b) In most cases, unwanted emissions outside of the frequency bands >>>> shown in these alternative provisions must be attenuated to the >>>> emission limits shown in �15.209. ... >>> >>> Aha! That means no free lunch after all. >> >> But how does this reconcile with the 20dB bandwidth, above? It's from the >> same paragraph. Transmitter can be 20dB down outside its band but still has >> to meet 11.209? Makes no sense. >> > >That's one reason why I wouldn't gamble on it. Lots of rules don't make >sense. But if anyone feels trampled upon such as the sheriff, he who has >more muscle or deeper pockets wins. Taxpayer pockets are often deepest >because it costs "nothing" :-(Point.>>>> ... In no case shall the level of the >>>> unwanted emissions from an intentional radiator operating under these >>>> additional provisions exceed the field strength of the fundamental >>>> emission. >>>> >>>> ..except for the "most cases". The interpretation from both labs is that (c) >>>> overrules (b). Harmonics from the hopping are certainly above 12.209. >>>> >>> It doesn't matter what the lab interprets. If the sheriff has this >>> brought to court and you lose, a major recall may follow because the >>> judge said so. Possibly wiping out the EMC lab and shaking up the place >>> where you work. >> >> I doubt the EMC lab is going down. It's a major corporation. >> > >Then they hopefully have good liability insurance, just in case. And >your company might be more protected as long as this large EMC company >blessed the gear.They did. Big international company.>>>> Our box, without the radiator passes 12.209 (below for information) but the >>>> radio does not, outside its band. The radio has a separate cert. <scratches >>>> head> >>>> >>> If the radio doesn't pass I'd be rather concerned. >> >> It doesn't. Interestingly, the 2.4G model does (but the harmonics are >> significant). I questioned it, but no one likes the bearer of bad news. >> > >Ok, that's up to corporate mgmt I guess. In medical we take such things >seriously because the next bearer of bad news might be cruising into the >parking lot in a car with government plates. No joke, that happened to a >large ultrasound company. I bet some bigshots stood there with egg in >the face.I'm sure it wasn't egg. ;-)>>>>>> ... The problem is that it takes a few more hours to >>>>>> guarantee that it meets the "no go zone" edges. ... >>>>> Now wait, are you now saying there are areas where it must meet class B? >>>>> If so, that's what I was saying all along. >>>> In the restricted zones, yes. Outside of those zones it apparently does *NOT* >>>> have to meet class A/B. They looked at the spectrum and saw one place where >>>> we were close. They made sure that pup was outside the (frequency) window and >>>> all was goodness. It *was* over the Class-A line but would have passed (and >>>> actually did when the module had its cert done). >>>> >>> Hopefully they are right ... >> >> Right about the interpretation? I'm not convinced either. >> >>>>> ... I stumbled onto this because >>>>>> the radio module does *not* meet the unintentional limits by itself. I turned >>>>>> it off and our box passes with 12dB to spare. If they can radiate like >>>>>> radium, why can't we? ;-) Seems all it takes is a redefinition of what the >>>>>> "intentional radiator" is. >>>>>> >>>>> Ok, intentional in the allowed band. I can't imagine they allow >>>>> excessive radiation _outside_ the permitted band. That would swing the >>>>> doors wide open to abuse. >>>> No, out-of-band must be 20dB below the in-band. ...didn't make any sense to >>>> me, either. >>> >>> Way I read the law above it ain't so. Not across the whole frequency range. >> >> At what frequency then? The rule makes no sense. > > >That's what I don't understand either. There may possibly be buffers >between your band and any important stuff. But sometimes not. For >example, there is no buffer between the DECT and the cell band. Your >DECT spills over and the lawyers of some telco giant might be all over you.Not according to the regs, there isn't. The process used by both cert labs is to measure the heavy hitters (above the class A/B lines) and make sure none of them are in the forbidden zones. It's a little tougher than the normal unintended radiator test because there are more edges to be concerned with.
