[Elecraft] Local Noise Problem

[David Cutter]

I'm looking forward to a time when all domestic lighting can be run from a 
12V supply at the main switchboard.  With led lights progressing as they 
are, I can see no reason for continuing to build houses with high voltage ac 
for lighting.  The wiring will be cheaper and safer and hopefully that will 
be a driving force for change.  Indeed a lot of domestic equipment outside 
the kitchen can also be run from 12V (I'm thinking of laptops, lcd tv, 
audio, gaming, side lamps).  If governments can ban incandescent light bulbs 
to save energy, then why not change the building regs to encompass new 
lighting systems when they come into mass use.  One might beget the other.

This will concentrate noise producing power sources and make them easier to 
treat, especially being adjacent the main earth/ground point into the house.

David
G3UNA



> On 4/2/2011 6:21 AM, Jim McCook wrote:
>> There is a very serious problem with the local noise source from low
>> voltage lighting systems.  These are sold as pendants, single lights, or
>> multiple lights on a support, such as a bar.  The retailer supplies them
>> with a choice of two types of transformers, either a regular magnetic
>> type (non interfering), or an "electronic" supply, which is a very noisy
>> switching supply.  The latter is most popular because it's small enough
>> to be contained within the smallest fixture.
>
> SNIP
>
>>   This is a
>> noise source that could seriously affect our hobby when new construction
>> begins en masse again.
>>
>
> Absolutely on target, Jim. I inherited a half dozen of these little
> monsters in the home I bought in California five years ago. There are
> two major components of the probem -- first, that these types of devices
> are exempt from Part 15, thanks to ARRL being asleep at the switch when
> the exemption was made (perhaps so focused on BPL that they saw nothing
> else), and to lobbying effort for "small government" that has
> essentially gutted the FCC.  Second, a real 12V transformer big enough
> to handle the load of these lights is at least 2-4X larger than the the
> limited space available in the electrical back-box for the fixture. So
> from a practical point of view, these switching power supplies are the
> only option. Those sold by the electrical supply houses here in Santa
> Cruz county, CA, are unbranded and carry no FCC labels.
>
> One piece of good news -- most, if not all, of the noise is radiated as
> a common mode signal on the AC power wiring, so  a good AC line filter
> can make a big dent in the RFI.  I was able to fit a filter in the
> backbox with one of these power supplies. It's also possible to suppress
> the noise with a multi-turn toroid choke plus a line-voltage rated
> capacitor across the line. There are two pieces on my website about this
> -- one on RFI and Ham radio, and the other specificcally about these
> filters -- how to use them and where to buy them.
>
> http://audiosystemsgroup.com/publish.htm
>
> 73, Jim Brown K9YC
>
>