En EETimes están publicando una serie de interesantes artículos sobre EMC, Compatiblidad Electro Magnética:
http://www.eetimes.com/design/analog-design/4217742/EMC-Basics--8--An-introduction-to-troubleshooting-EMI-problems--con-t-?cid=NL_PowerManagement&Ecosystem=power-management-designComo no sé si todos pueden verlos, ya que me parece que solo se puede acceder si se es usuario registrado, voy a hacer un copy/paste sobre la parte que me ha parecido más relevante y de mayor interés:
[There are two major components to emissions problems: hidden transmitters and hidden antennas. Even though they are not really hidden, most designers don't see them as transmitters and antennas (RF designers being an exception, of course.) But the electrons don't care—if it looks like a transmitter and an antenna, it's time to party.
The primary hidden transmitters in most systems are digital circuits. Highly repetitive signals such as clocks and clock-like signals (busses, repetitive control lines, etc.) generate strong harmonics. But even switching power electronics (power supplies and motor drives) can get into the act. As a helpful hint, we usually assume the first twenty harmonics of any repetitive signal are potential transmitters.
But even lower frequency circuits can be hidden transmitters, thanks to parasitic oscillations. Long a problem with vacuum tubes, we've seen a significant increase these unwanted oscillations in solid state voltage regulators, op amps, and other more. As a helpful hint, these usually occur above 100 MHz.
The hidden antennas are highly dependent on physical dimensions and frequency. The higher the frequency and the longer the antenna, the more the radiation. We usually assume anything over 1/20 wavelength is an efficient antenna. That means six inches at 100 MHz, and about 3/4 inch at 1 GHz.
As such, cables are very likely hidden antennas, followed by traces on circuit boards and even the components themselves in the GHz range. Openings in shielded enclosures can act as "slot antennas", and follow the same guidelines. A two-inch slot at 300 MHz leaks like a sieve.
So how do we troubleshoot these emissions problems? Here are five quick suggestions:
•Turn off clocks or change their frequencies to see if the emissions more or disappear. This can isolate the hidden transmitters.
•Use sniffer probes to identify hidden transmitter circuits. These are small hand held magnetic probes you connect to a spectrum analyzer. Since they are quite localized, you can quickly sniff around a circuit board for hot spots for emissions.
•Remove cables to see if the emissions change. This can isolate the hidden antennas.
•Use current probes on the cables. These are high frequency probes you clamp on a cable and connect to a spectrum analyzer. Currents in excess of a few microamps are suspect.
•Shield the entire enclosure with aluminum foil. This is very useful in identifying any hidden antennas in the mechanical enclosure.]
Como dice el texto: But the electrons don't care. Como lectura complementaria este texto que ya se había puesto en otra ocasión, para quienes todavía no lo hayan leído:
http://www.mediafire.com/file/bfd7qo3xv64goas/Ceros%20Unos%20Datos_Jitter.pdfSaludos, Raúl
