Topband: Home Depot LED bulb interference.

[Lennart M]

Hi Jim et al,
There is a third way, often overlooked.
The radiated power is rectified - at least to some degree by lousy
connections, i e aluminium fences to Al poles, which then reradiate. Look
for those sources and poor connections as well.
73
By the way, 160 is still open
Len
SM7BIC 

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Från: topband-bounces at contesting.com [mailto:topband-bounces at contesting.com]
För Jim Brown
Skickat: den 27 april 2012 19:35
Till: topband at contesting.com
Ämne: Re: Topband: Home Depot LED bulb interference.

On 4/27/2012 10:10 AM, Wayne Mills wrote:
> I also note that the experiment in the You Tube video is measuring 
> noise on the mains line. What about radiated noise? Since the sample 
> is referenced to ground, it might be representative of any radiation. 
> The noise that I observed was affected by my hand in the vicinity of 
> the lamp, surely radiation. Not good.

Some fundamental RFI concepts.  Nearly all RFI we hear in our receivers is
radiated by something.  It may be radiated by the noisy device, or it may be
radiated by a cable connected to the noisy device.  In the EMC world, noise
radiated by the cable is called conducted noise, because the noise is
conducted out of the device to the cable.  But it's still radiated noise.

Noise can be coupled to cables (like the power line) as a differential mode
voltage (that is, between the conductors) or as a common mode voltage (that
is, on all the conductors in the cable).  A common mode voltage causes the
cable to carry noise current, and any wire carrying RF current will act as a
transmitting antenna.  It is that radiation that we most often hear in our
radios.

Ferrite common mode chokes are an effective way to kill common mode current,
but they must be tuned for the frequency(ies) where the noise is present.  A
capacitor that shorts out the differential voltage can kill that component.

Several mechanisms (beyond the scope of a simple email) convert differential
voltage to common mode current, and common mode current to differential
voltage.  Thus, a serious ferrite common mode choke is always a good thing.

http://audiosystemsgroup.com/RFI-Ham.pdf

LED lights work on low voltage DC, and the trash from products like this is
usually from the switching power supply that converts 120VAC to that low
voltage DC.  We know about switching power supply noise -- it can be quite
frequency-dependent, it is generally drifty, it usually appears as a hump of
noise in a spectrum display, and the relative strength in any frequency
range will depend both on the waveshape of the noise in the device and the
effectiveness of both internal and external wiring as an antenna.

Finally, we as hams must do our part to cause vendors to clean up their RF
noise.  If you buy a product that's noisy, return it as defective and demand
your money back.  Tell them why you're returning it -- that it makes your
radio and TV unusable, and that it violates FCC Rules.

73, Jim K9YC
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