Hi Colin and the group. You mentioned: <The ferrites will greatly minimize this induced current and so practically eliminate this effect.>
I find ferrite sleeves, snap-on and otherwise, incredibly useful for reduction of emissins from cables, but for HF feeder and antenna drive purposes I find them a bit iof a nuisance. I haven't studied these especially, apart from the manufacturers data etc., but I find these ferrites to be very lossy. This 'lossiness' is invaluable for providing an HF dumpng ground for any loose HF resonant energy, or HF ringing energy on high speed digital lines for instance. If you drive coax lines with high speed data, all those 0/1 transitions are very fast, and quite capable of kicking the coax screens into a resonant condition sufficient to provide a very significant peak somewhere, particularly noticeable on video outputs from PC's etc. Especially bad if cables are incorrectly terminated of course. These ferrites provide some impedance to act as a low pass filter, and also provide enough losses for the ferrite to absorb that blocked energy. If there was no losses I reckon the resonance would simply move somewhere else in the spectrum. I suppose that if there was sufficient HF activity in these cables with ferrites fitted, one could expect the ferrites to get hot! I haven't noticed this particular phenomenon yet.... Has anyone tried the trick of running a 3mm copper wire through the Ferrite with the suspect cable, and soldering it into a 'shorted turn' configuration. Got some interesting results, not spectacular, just interesting Just a twopence worth for the opinion bucket. Chris Dupres Surrey, UK. --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
