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:
>>> [...]
>>>
>>>>>>> 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.
>>>>
>>> Some of my stuff must be measured at 1m. At 3m you wouldn't be able to
>>> see much anymore, certainly not on a spectrum analyzer. At 10m there'd
>>> be nothing. But the standard is rather detailed about how the chamber
>>> must look like. For example, numerous antennas, several rotating stirrer
>>> plates, and so on.
>>
>> ?? If I can't see it at 3m or 10m, for that matter, why do I care? ...
>
>
>The RTCA/DO-160 standard does care, and some of the stuff here has to
>comply. Else the FAA will have a bone to pick.
Ok, we're not concerned with the FAA.
>> ... 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.
>>> [...]
>>>
>>>>>>> Goes from close to DC to a little above 3GHz.
>>>>>> What sort?
>>>>>>
>>>>> Mine is the Icom R-1500. Has a mini console for quick checks when I
>>>>> don't want to fire up the PC. If you go PC-only then there's the similar
>>>>> PCR-1500 for about $100 less.
>>>> I'll take a look at it. Thanks.
>>>>
>>> An hour ago it did another fine job. Got three little transmitters here
>>> that are stuck. In order to diagnose this I had to see if the various
>>> data packets were still being transmitted, over all that din these
>>> things created. Fired up the Icom and sure enough, could hear a distinct
>>> faint "brrripp" whenever a packet was sent and the sound of it changed
>>> when I sent different packets. Very deep inside of what sounded like
>>> Niagara Falls from 10ft away. Now try that with an analyzer ...
>>>
>>> [...]
>>>
>>>
>>>>>> If you read the regs, at least for FHSS radiators in the ISM bands, anything
>>>>>> outside the band, and outside one or two do-not-collect-$200 bands, must only
>>>>>> be 20dB down from the in-band radiation. Easy-peasy, when you're radiating a
>>>>>> hundred or two milliwatts.
>>>>>>
>>>>> Huh? So you can be way above class B limits in, say, the aircraft bands?
>>>> "outside one or two do-not-collect-$200 bands"
>>>>
>>> Well, I bet you'd get in trouble no matter what if anything leaked. FM
>>> band, police, air, even TV. And if you step on some Lt.Colonel's radio
>>> link, oh boy ...
>>
>> Why? It's an intentional radiator. It passes that test.
>>
>
>It's not supposed to intentionally radiate at, say, 155MHz because the
>local sheriff will have something against that.
As long as it's 20dB below the fundamental, apparently the local sheriff can
go scratch.
>>>>> Do you have a link there?
>>>> I meant to look it up again today but got busy doing real work. (Some nitwit
>>>> decided to save $20 and leave off the solder mask on a proto board).
>>>>
>>> Oh great! He's earned himself a spot in the hall of blame I suppose :-)
>>>
>> It's worse than that. The board is 2-layer (fortunately rather simple) with
>> ground and Vcc pours top and bottom. It's almost impossible to solder
>> anything without bridging. Getting solder to flow under the LEDs was a RPITA.
>> "He" doesn't much care about blame, though it's not going to happen to me
>> again.
>>
>>>>> If you also know anything like that in the
>>>>> tax code I think lots of people would be all ears :-)
>>>> ;-)
>>>>
>>>>>>>>> If the mfg waffles on the stickers and cert copies, run.
>>>>>>>> That's not my point.
>>>>>>> Ok. Then why not just slap on the sticker, do only the regular EMC and
>>>>>>> be done with it? Of course the EMC lab needs to know about the
>>>>>>> intentional radiator part so they don't flag that.
>>>>>> Because the intentional limits are almost impossible to fail. We pass easily,
>>>>>> now, so there isn't any point in gaming the system, but the rules leave the
>>>>>> door wide open.
>>>>> Sure, when you are a good designer or use pre-cooked modules they are
>>>>> easy. But why spend that extra money to test if it's already done?
>>>> Because it makes passing a piece of cake. Can't fail! It probably wouldn't
>>>> have worked for the product we had real trouble with because we needed CE (and
>>>> all the rest of the alphabet soup, too)
>>>
>>> Well, I know for sure the Europeans won't let you get away with that.
>>> But I can't imagine the FCC would either. Because then just about
>>> everybody could put in intentional radiator in their product whether
>>> it's needed or not, just to dodge the smog check.
>>
>> That's what the regs say. I checked my interpretation with our test lab and
>> it agrees with theirs. ...
>
>
>Got any links there?
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, 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. 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.
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>
>
>> ... 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).
> ... 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.