[RFI] led bulb test

[Gary Smith]

Outstanding explanation.

Gary...wa6fgi


On 11/10/2016 8:07 AM, Jim Brown wrote:
> Hi Greg,
>
> Outside of compliance test labs, our concern is NOT to determine 
> compliance with FCC Rules for emissions, which are not necessarily a 
> good indicator of the extent to which a given device will radiate 
> enough noise into our antennas to be problematic. A LISN (Line 
> Impedance Simulation Network) simulates the DIFFERENTIAL loading of 
> the noise source by the power system, but most noise is radiated 
> either by 1) the combination of poor circuit layout and poor 
> shielding, or 2) as a COMMON MODE signal on ALL wiring connected to it 
> (that is, not only the power line).
>
> As a point of clarification, what EMC rules call "common mode" is 
> voltage between neutral and green, while what WE call common mode, 
> because it's what causes radiation, is the sum of all current on the 
> cable in question. In most products, that turns out to be the current 
> on the green wire and on the shields of interconnecting cables. The 
> most common cause of common mode noise current is what audio 
> professionals call "the Pin One Problem," where the cable shield or 
> the AC green wire fail to bond to the shielding enclosure at the point 
> of entry, but instead go THROUGH the shielding enclosure to the 
> circuit board. This puts noise current on the Green Wire, which goes 
> right past a commercial line filter external to the noise source. That 
> filter CAN be effective only if it bonds the Green Wire to the 
> shielding enclosure by a "zero length" lead, ideally mounted to the 
> shielding enclosure.
>
> As I see it, a key benefit of using an SDR in chasing RFI is in 
> identifying the noise -- that is, is it a power system device like an 
> SMPS or variable speed motor controller, the clock for some sort of 
> digital electronics, or impulse noise.  An SDR can also help by 
> letting us monitor more spectrum at once as we switch the potential 
> noise source on and off.
>
> Bottom line -- as hams, we want to know if a given device will bother 
> us, not whether it complies with FCC Rules.
>
> 73, Jim K9YC
>
> On Thu,11/10/2016 5:26 AM, Greg Troxel wrote:
>> Jim Brown <jim at audiosystemsgroup.com> writes:
>>
>>> Thanks for posting this work. Several comments. First, the use of an
>>> SDR to look at spectra of the noise is a really good idea. I'm
>>> currently working on updates to the ARRL Handbook, and this is
>>> something I'm suggesting. The SDRPlay ($130) is a particularly good
>>> choice, because it has a very wide tuning range and can display a
>>> large chunk of spectrum at one time.
>> I have also been trying to make measurements, but so far just looking at
>> a PX3 hooked up to either an attic dipole or a proper outside antenna.
>> Operationally for me, if I can't hear the difference between on/off on
>> any band on either antenna, with a desk lamp in the shack, it's good
>> enough.  But I'm starting to try to do this listening on closed bands;
>> my 80m noise level is vastly lower midday than evening, which I suspect
>> is typical for relatively quiet locations.
>>
>> It seems that for repeatable quantitative measuremnts, one wants a Line
>> Impedance Stabilization Network and a spectrum analyzer, but this is at
>> best $2K.  I have borrowed a LISN (which is large and heavy) and intend
>> to hook it up (with at least a 20 dB pad) to a KX3/PX3.  That's not a
>> proper SA, but should be pretty good within the ham bands.
>>
>> So I wonder if you are able to suggest (for the Handbook) how to
>> approach repeatability without buying or homebrewing a proper LISN.
>> Also, it would be good to discuss rough calibration of things like the
>> SDrplay to get measurements that are plausibly close to using real lab
>> equipment.
>>
>> I say all this realizing that the audience includes people with varying
>> technical backgrounds and budgets.
>>
>> But overall, with some repeatability and rough calibration, it should
>> then be reasonable to build up a web database of results.   It seems
>> like the hard part is the LISN equivalent.  Perhaps that would make a
>> good kit, or perhaps I'm overestimating the parts cost/hassle.
>>
>> 73 de n1dam
>>
>
> _______________________________________________
> RFI mailing list
> RFI at contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi