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| Re: UK Advertising Standards Agency takes a stand against Power Cables [message #329304 is a reply to message #329298 ] |
Mon, 31 March 2008 06:45   |
 Bruno Putzeys
Messages: 631
Registered: November 2006
Location: Rotselaar (Belgium) |
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I should warn against cross-posting.
That said, jneutron's point is oversimplified. More precisely, he's suggesting that a mismatch between two transmission lines will produce a wideband attenuation. In reality, a mismatch will produce comb-filtering like effects, with some frequencies reinforced and others attenuated. So it is true that changing cables in an EMC test setup will change the result, but there is no way in which one cable will produce a net improvement over another. Also, transmission-line effects like these only play out at wavelengths comparable to or shorter than the length of the cable. Most mains borne RFI is in the <30MHz region (above that the line between conducted and radiated emission quickly blurs, for practical reasons).
We may safely say that this nit-picking is the kind of rearguard battle typical in pseudoscience: trying to discredit criticism without providing something more solid to replace it with. But if nits need picking, the least thing one can do is pick them correctly.
Have more faith, Bambi. The only right way of dealing with headlights is staring them down.
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| Re: UK Advertising Standards Agency takes a stand against Power Cables [message #329913 is a reply to message #329910 ] |
Wed, 02 April 2008 04:54 |
Bruno Putzeys
Messages: 631
Registered: November 2006
Location: Rotselaar (Belgium) |
Gold Member |
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| johnR wrote on Wed, 02 April 2008 11:27 |
Anything that gets through the power supply and intermodulates in an audible way with the audio could be said to matter.
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Quite, so an item (say a cable) that just changes things without actually making an overall improvement cannot be considered a solution.
Have more faith, Bambi. The only right way of dealing with headlights is staring them down.
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| Re: UK Advertising Standards Agency takes a stand against Power Cables [message #330189 is a reply to message #328116 ] |
Thu, 03 April 2008 07:56 |
Jakob2
Messages: 3
Registered: July 2007 |
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@ Bruno_Putzeys,
sorry for the crossposting, i did just think that is was the same topic and therefore another point of view might be of interest.
Taking the related length into account that could be infront of the wall outlet, the mains wire could be treated as tranmission lines and fall into the impedance region jneutron mentioned.
Due to the impedance mismatch between mains and "Kimber" reflection will occur and most likely some reduction of the conducted RFI will happen.
If the net result leads to improvement (means reduction of the RFI conducted) will depend on the source impedance of the mains source point, the length of the "IEC-cord" , dielectric used in the cord.
Due to the braid construction of the "Kimber" the pickup of RFI might be reduced too.
In the end the point of jneutron is just that an expert evaluation should have treated the subject in a more scientific way.
At that point i´d agree, but after reading of the CAP Code i realized that i did misunderstand the situation.
The CAP-Code Rule is:
"Before distributing or submitting a marketing communication for publication, marketers must hold documentary evidence to prove all claims, whether direct or implied, that are capable of objective substantiation.
Relevant evidence should be sent without delay if requested by the ASA or CAP. The adequacy of evidence will be judged on whether it supports both the detailed claims and the overall impression created by the marketing communication. The full name and geographical business address of marketers should be provided without delay if requested by the ASA or CAP."
So, as i hopefully now got it right, the expert should only evaluate if the papers presented by the advertiser are the substantiation required by the CAP-Code or not.
That is of course a totally different message.
So please accept my apologies for the misunderstanding.
Originally writter by johnR
IIRC, test gear for conducted EMI (at least in Europe) assumes a 50 ohm source impedance for mains power to an appliance, not 500 ohms.
That´s true, but is just a standard.
It normal situations the mains does not have a source impedance of 50 ohm and the audio gear connected does not have a load impedance of 50 ohm, so it is quite different in real world applications.
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| Re: UK Advertising Standards Agency takes a stand against Power Cables [message #330512 is a reply to message #330189 ] |
Fri, 04 April 2008 05:25 |
johnR
Messages: 346
Registered: April 2007
Location: Kent, UK |
Active Member |
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| Jakob2 wrote on Thu, 03 April 2008 13:56 |
Originally writter by johnR
IIRC, test gear for conducted EMI (at least in Europe) assumes a 50 ohm source impedance
for mains power to an appliance, not 500 ohms.
That´s true, but is just a standard.
It normal situations the mains does not have a source impedance of 50 ohm and the audio gear connected does not have a load impedance of 50 ohm, so it is quite different in real world applications.
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Yes, but a standard that is based on conditions that are wrong by an order of magnitude isn't much use. I was just questioning the 500 ohm figure. Appliances are connected to mains by a relatively small range of cable types, which I would expect to have characteristic impedances (at RF) falling in a similarly small range. A standard must be based on some typical real world conditions in order to be meaningful. (That doesn't mean they all are, of course).
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| Re: UK Advertising Standards Agency takes a stand against Power Cables [message #337244 is a reply to message #328116 ] |
Mon, 28 April 2008 06:56 |
Rigby
Messages: 30
Registered: May 2004 |
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I could be wrong, but I believe the Advertising Standards Authority's remit is purely a reactive one. In other words, it exists in order to respond to complaints, and is obliged to do so. So it's not really a question of whether they are 'going after' particular advertisers; it depends whether they receive complaints from the public or not. There have been some reasonably high-profile adjudications against people marketing alternative medicines and nutrition supplements too, notably the appalling "Doctor" Gillian McKeith.
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