The discussion focuses on coupling noise generated by the chattering of relays, specifically addressing electromagnetic interference (EMI) produced during contact opening. It is established that the noise originates from the relay contacts rather than the coil. Participants suggest using short antennas connected to the spark gap to enhance radiation and propose winding wires around the relay casing to couple interference effectively. The breakdown of the gap occurs rapidly, potentially in picoseconds, leading to oscillatory energy across various frequencies.
PREREQUISITESElectrical engineers, hobbyists working with relays, and professionals involved in EMI analysis and RF circuit design will benefit from this discussion.
I believe the radiation occurs because when the contact starts to open, the inductance of the coil creates a forward EMF and this then causes the gap to break down again. This breakdown is very fast, and you may know that one of the early radio experimenters, Bose, obtained results using a spark gap at 40 GHz. So we may assume it breaks down in picoseconds. Any energy that is stored in the capacitance of the wires will then be converted into oscillatory energy at all frequencies at which the wires have a resonance. To obtain "good" radiation, I suggest connecting short antennas to each side of the spark gap, to form a dipole, or opening out the wiring each side of the contact to form a loop. Remember that the pulse in the coil itself will be quite slow.Nikhil N said:
Thanks for the replay. Now what's my doubt is U have suggested to connect small antennas to each of the spark gap, by this u have meant to connect the antennas to the coil ends ? Can I wound the wire to which I have to couple the noise onto the relay casing in order to couple the interference?tech99 said:
The noise comes from the contact, not from the coil.Nikhil N said: