Akula eternal lantern 4

[MarkE]

MarkE


What would you propose to block EMI from 8kW radio transmitter put inside a box ?




I heard Richard Willis has such problems with EMI radiation.

I heard that Richard Willis' dropped phone numbers months ago, and now his web site registry has expired.
The shielding methods that will be most effective depends on whether wires have to come out of the box or not.  If they do, and they are long, then they are likely the biggest source of EMI.

In the case that no wires come out of the box:  An ordinary steel box with EMI gasket material around all seams, where the EMI gasket material makes gas tight contact with the box material (preferably with a tin or other conductive plating) will make the box pretty EMI tight. 

In the case that wires come out of the box, then in addition to the box above, the wires need to pass through a suitable EMI filter that is bonded to the box.  There are many off the shelf filters available.  The filter design depends on:  The voltage and currents that must be supported, the frequency of the current that must be passed, and the amount of noise that is on the lines unfiltered.

[MarkE]

@MarkE,

A transistor radio with a retractable aluminum antenna would be protected while completely isolated from the cage conductor. Extending the radio antenna enough to make contact with the cage conductor would turn the cage into an antenna! Got it?

An antenna works by having energy impinge on it that gets guided to a sensing circuit.  The energy travels along the surface and for MHz and up signals penetrates only a tiny bit into the surface of the metal.  The better the conductor, the less the penetration at any given frequency.  Deeper inside the metal there is virtually no net energy because the impinging field is virtually completely canceled by the image current of the surrounding metal. 

If you have a strong enough signal, the finite resistance and inductance of the metal structure will develop detectable voltage drops.  Those voltage drops conduct current through capacitance to whatever circuit is inside the box.  That capacitance reacts with the inductance of the box and circuit board structures establishing resonances.  EMC engineers push those resonant frequencies up by making multiple connections to the metal structure at spacings that are as small as possible and/or insert energy absorbing materials like carbon loaded foam to damp the resonances.  In extreme situations more than one level of box is used.

[forest]

MarkE


The problem is when device has output wires carrying high frequency currents of many amps.A shield like copper tube around wire ?

[MarkE]

MarkE


The problem is when device has output wires carrying high frequency currents of many amps.A shield like copper tube around wire ?

If the wires are contained end to end in sealed metal enclosures then there will be very little radiation.  If the shielding were superconducting there would be no radiation.  In effect what you have is one big sealed Faraday Cage.  Except for rigid coax, the cable shielding is never perfect, and the bond to the metal enclosure is almost never solid.  That means that an antenna or antennae exist, and then the task is to decouple the internal noise from those antennae.

[synchro1]

@MarkE,

You're a nauseating and obnoxious fraud. Get a life!