Grounding cable shields

[Matt Syson]

One problem with the whole subject is that so many aspects depend on multiple factors often relating to the one specific situation (location). Whether it is in a building which has bad physical power wiring (physical loops between live and return currents, equipment (dimmers etc) mobile radio or phones etc.
Speaking of radio I think some would refer to 30KHz as being near the bottom of the radio frequency bands. My clock (in France) receives 60KHz from Rugby in England and as it is a clock made for the UK is every accurately incorrect (being an hour slow) since the time signal is referenced (NPL reference) to UK time. So, back to balanced audio links once you have at least half decent twisted pair wire the ability to reject unwanted interference of any sort boils down to the characteristics of the 'send' and 'receive' circuits which again can be influenced by the enclosure and connectors. I would guess that an XLR type connector will manage to retain good 'balance' over a wideband, certainly compared to a TRS jack plug. Whether this proves to be the 'archillies heel' on a piece of gear is for others to say.

 

[Bo Deadly]

Speaking of radio I think some would refer to 30KHz as being near the bottom of the radio frequency bands. My clock (in France) receives 60KHz from Rugby in England and as it is a clock made for the UK is every accurately incorrect (being an hour slow) since the time signal is referenced (NPL reference) to UK time.

Interesting. I wonder what the antenna for that would have to be.

 

[ruffrecords]

Interesting. I wonder what the antenna for that would have to be.

Well UK Radio 2 long wave (AM) is on 1500m which is 100KHz, so 60KHz will have a wavelength of 2.5 kilometres. So a half wave dipole would be 1.25km long or, if you could build it, a quarter wave vertical whip would be 625m tall. There are plenty of tricks you can use to reduce the physical sizes (base loading for instance) but prior to 2007 if you drove past Rugby on the motorway you can see the antennae covering vast acreages.


If you are interested, wikiP has a good article: Rugby Radio Station - Wikipedia
Cheers

Ian

 

[ccaudle]

I wonder what the antenna for that would have to be.

The transmit antennas are huge. The receiving antenna would typically be a coil design so that not much space is required.

 

[ccaudle]

guess that an XLR type connector will manage to retain good 'balance' over a wideband

I think the biggest problem with XLR is that the standard calls for shield connected to pin 1, rather than a coaxial shield-to-shell connection, which causes an increased inductance compared to coaxial termination, and a capacitance imbalance since pin 1 is closer to one of the signal pins than the other.
The Neutrik "EMC" line of cable connectors addresses that with a coaxial connection to the shield which is capacitively coupled to the shell. They are noticeably more expensive than the traditional connectors because of the extra parts involved.