Tom, these people may well be audiophiles, however their paper is
entitled "Suppression of powerline noise, with isolation transformers"
was presented by B.C.Gabrielson & M.J. Reimold at EMC Expo 87, May 19-
21, San Diego....and available on the internet....John G3JVC.
On Sat Jul 1 14:02 , 'Tom W8JI' <w8ji@w8ji.com> sent:
>> the secondary. This beast is heavy, and you need a fork
>> lift to move it. The reason I specified two electrostatic
>> screens is that in an American paper I read, on the
>> internet, on feeding AC supplies to EMC/Faraday screened
>> rooms, one or two isolation transformers were recommended,
>> with two electrostatic screens per transformer, the
>> reasoning being complex, so I just accepted it.....
>
>The Internet is like Alice's resturant. We can find almost
>anything we want on the Internet. A portion of it will be
>accurate, much will not. Especially when it is something
>designed to sell a certain product, or a clan or clique
>thing like AudioPhool technical papers.
>
>..I also had a proper ground system laid, by a firm of
>lightning
>> protection specialists...certified ground resistance now
>> just 2.1ohms...the
>
>What does that have to do with RF noise, which is what we
>hear on receivers?
>
>> incoming public supply is taken to the primary winding of
>> the isolation transformer, the output, via a screened
>> lead, to the shack. Both electrostatic sceens are taken
>> back to the newly installed ground system, and there are
>> now no connections between the public supply and my
>> shack....the result, all the electrical noise has now
>> gone, and apart from the radiated occasional radiated
>> emissions, my radio background noise has dropped back to
>> that of 40 years ago...
>
>You might have revisited the shack equipment, antennas, and
>connections before going through all those expensive
>solutions.
>
>The only noise that can "get into" our receivers is RF
>noise. The only way in should be through the antenna
>connections. Any other path should easily be down 100dB or
>more.
>
>I'd have looked at then installation of my feedlines and
>their interface to antennas first.
>
>>.In text books of that time, the electrostatic screen was
>>described as a method of preventing the feed back of
>>interference into the public supply, by the consumer,
>>however, it was explained to me, by my local transformer
>>manufacturer, that it was only looked upon as a safety
>>measure, by the transformer manufacturers,
>
>The manufacturers are correct. It primarily is a safety
>device. So is bonding transformer laminations at ONE common
>point and grounding them there, with all other areas of the
>lamainations insulated.
>
>>with the improved high termperature varnishes for the wires
>>used in winding, they could save a small amount of money,
>>by not including the copper electrostatic screens....which
>>may be, why our received noise levels have been climbing in
>>the past decades
>
>Lack of shields in transformers has not increased noise. The
>noise increase is because of the increase in mains voltages,
>and because switching supplies and similar RF producing
>devices have increased.
>
>A primary shield is actually very little assurance noise
>doesn't get through a system. It's a cheap additional
>band-aid when initially winding a transformer, but the
>problem is a lack of suitable line bypass capacitors and
>small series chokes.
>
>Anything you did with that big heavy expensive transformer
>at radio frequencies, I can do better with something I can
>hold in one hand....and at 10% of the cost.
>
>You really ought to learn why your radio system is partially
>using the power mains as an antenna. That's the real
>question.
>
>When radios were built on an unshielded wooden chassis, when
>bypass caps were expensive and erratic radio frequency
>impedances, before we had ferrites and other modern
>components, and before good components at radio frequencies
>were obtainable, things were done differently. Solutions
>necessary back then are very often totally meaningless
>today. The key is always understanding how things actually
>work, and not relying on accidents to patch problems.
>
>73 Tom
>
>
>--
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