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
-----Ursprungligt meddelande----- Från: [email protected] [mailto:[email protected]] För Jim Brown Skickat: den 27 april 2012 19:35 Till: [email protected] 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 _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
