[RTTY] Multiple cables on 1 core

[Ian White]

Bostjan and I are doing the same thing practically, but we are thinking about it in two entirely different ways... and that difference is important.

I meant exactly what I said! The most important aim is to connect all the chassis and frames TOGETHER so that all the units are at the same RF potential RELATIVE TO EACH OTHER.  Zeroing-out any differences in frame potential between different units is the most effective way to prevent common-mode RF currents on the interconnects. 

"Ground" is not a helpful concept in any discussions about RFI, because it depends on what each individual person imagines "ground" to mean. For example, many people confuse "ground potential" with the potential of the mains safety earth conductor. The difference doesn't matter at 50/60Hz - and safety earth connections are mandatory - but those conductors are too long to be relevant to this discussion about RFI within the shack.

So really my only disagreement with Bostjan is about the use of that "g" word... and [RTTY] is probably the wrong forum to take that further.


73 from Ian GM3SEK

>-----Original Message-----
>From: Bostjan Voncina - S55O [mailto:bostjan.voncina at gmail.com]
>Sent: 30 September 2014 08:23
>To: Ian White
>Subject: Re: [RTTY] Multiple cables on 1 core
>
>Hello!
>
>As Ian Said:
>"The best strategy is first to bond the chassis and frames of all
>equipment together, using the shortest possible length of low-impedance
>conductor (eg a broad strip of copper along the rear of the table-top).
>Do that bonding first, and then see if any ferrites are needed at all,
>and try to identify and treat the individual problem conductors."
>
>
>Ian surely ment to connect all chasis to a single point of good grounding,
>dont make a chain from them (radio to PA then PA to interface...etc) This
>will cause RF problems in itself and also it's problematic from the aspect of
>different electrical potentials of different hardware. And you also make an
>antenna out of it (for RF ).
>
>
>Better use a thick and good grounding (strip...) and connect all groundings
>to that strip. Work best if it's at the same point, but if it's not possible, you
>can use a thick enough grounding system, so the potentials of the different
>gadgets and equipment are the same (vs ground). When you connect all
>grounds, make sure it's a grounding system different as the main (electrical)
>ground of the house. So it would be good to put something in the ground
>and then connect all RF grounds to that.
>
>That's how we eliminated lots of problems @ s51a
>
>
>Best of luck
>
>
>Boštjan S55O
>
>
>
>2014-09-30 9:05 GMT+02:00 Ian White <gm3sek at ifwtech.co.uk>:
>
>
>	>
>	>I'm re-doing some RTTY interfacing here in the shack and just
>wonder -
>	>can you use the same ferrite core for 2 different cables wound
>	>together?  Sure would make for a neater lashup.  Thanks and 73
>	>Tom W7WHY
>
>	The supposed purpose of ferrite cores on interface leads is to
>suppress
>	any stray common-mode RF currents between different parts of the
>system
>	(most often, between the transceiver and the PC). In that case, it's
>	probably OK to use the same core for bundled conductors that are
>going
>	to the same destination.
>
>	But in real life it isn't always so clear-cut. Many people's idea of
>	"using ferrite" is a single pass through one ferrite bead, which
>doesn't
>	make a very effective RF choke... but it does make quite an effective
>RF
>	transformer. If you pass several conductors through the same core,
>the
>	transformer action means that common-mode RF current carried
>on one
>	problem conductor will then be shared onto all the others
>conductors as
>	well... so in some cases sharing a common core can make RFI
>problems
>	worse.
>
>	Because of the risk of sharing common-mode current, it isn't a good
>idea
>	to use a common core for conductors that are going to different
>	destinations.
>
>	The best strategy is first to bond the chassis and frames of all
>	equipment together, using the shortest possible length of low-
>impedance
>	conductor (eg a broad strip of copper along the rear of the table-
>top).
>	Do that bonding first, and then see if any ferrites are needed at all,
>	and try to identify and treat the individual problem conductors.
>
>
>	73 from Ian GM3SEK
>
>
>
>	>-----Original Message-----
>	>From: RTTY [mailto:rtty-bounces at contesting.com] On Behalf Of
>Tom
>	>Osborne
>	>Sent: 29 September 2014 23:55
>	>To: rtty at contesting.com
>	>Subject: [RTTY] Multiple cables on 1 core
>	>
>	>HI all
>	>
>	>I'm re-doing some RTTY interfacing here in the shack and just
>wonder -
>	>can you use the same ferrite core for 2 different cables wound
>	>together?  Sure would make for a neater lashup.  Thanks and 73
>	>Tom W7WHY
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