Phobic

A test for power cables

Recommended Posts

1 hour ago, Fourlegs said:

That aside, there seems to be a cogent argument for only grounding the shield at the source end and that connecting the shield to ground at both ends might promote extra interference and/or ground loops (it is entirely possible that the ground at each end will be at a different potential). For me I have always (and will continue) to only connect the shield to earth at the mains plug end.

If the shield/screen is connected to earth in the plugs at either end of the cable it is unlikely to produce a ground loop. 

Share this post


Link to post
Share on other sites
1 hour ago, dave said:

I think I am suggesting that it will effectively form part of the transmitting antenna, the transmission being the audio. Well a little bit of it.

And of course everything will be interacting with "RFI" at the same time.

isn't the answer though to just shield the power cable?

stop the pixies getting in or out!

Edited by Phobic

Share this post


Link to post
Share on other sites
33 minutes ago, Phobic said:

isn't the answer though to just shield the power cable?

stop the pixies getting in or out!

My mind was being led more in the direction of balanced, screened speaker cables..........

Edited by dave

Share this post


Link to post
Share on other sites

There was a fair amount of discussion about connecting the earth at one end or both here (click on the arrow at the top right to jump to where this first came up in the thread):

  • Upvote 1

Share this post


Link to post
Share on other sites
Moderator

It's also worth pointing out that we're not talking about the signal ground here, we're talking about the safety earth, which will be connected to the equipment case and which may (or may not) be referenced to the signal ground. For the mains cable then, even if there is a (very, very) small difference in ground potential between the plug and the other end, connecting the screen at both ends should mean there is no difference in potential between the screen and the case earth anyway. And even if there is, what difference will it make? The only point of the screening on a mains cable is to stop EMI/RFI getting in and/or out.

Share this post


Link to post
Share on other sites
3 hours ago, dave said:

  I would like to think that the unbalanced audio signal traveling from the all in one via the speaker cable to the speaker would act like a very inefficient transmitting antenna.

Yes but an extremely inefficient transmitter as the speaker cable is so short relative to the wavelength of audio signal in the cable (20 kHz would have a wavelength of ballpark 12 km).

  • Upvote 1

Share this post


Link to post
Share on other sites
Moderator
7 minutes ago, MartinC said:

Yes but an extremely inefficient transmitter as the speaker cable is so short relative to the wavelength of audio signal in the cable (20 kHz would have a wavelength of ballpark 12 km).

The old radio comms installation at Rugby used to transmit 16KHz signals for submarine communications, using transmitters in the hundreds of kilowatt range. An old colleague of mine worked there for a while - apparently,once you switched on the fluorescent lights in the office it was impossible to switch them off because the phosphor continued to be excited by the 16K signal!

  • Like 3

Share this post


Link to post
Share on other sites
2 minutes ago, Tony_J said:

The old radio comms installation at Rugby used to transmit 16KHz signals for submarine communications, using transmitters in the hundreds of kilowatt range. An old colleague of mine worked there for a while - apparently,once you switched on the fluorescent lights in the office it was impossible to switch them off because the phosphor continued to be excited by the 16K signal!

There was an art installation some years ago near Bath where they "planted" a load of fluorescent tubes in the ground under some electricity pylons / transmission cables, and they were all "magically" illuminated from the current running though the cables passing overhead. Was an interesting piece, science meets art :D

  • Like 1
  • Haha 1
  • Upvote 1

Share this post


Link to post
Share on other sites
Super Wammer
3 minutes ago, Rayymondo said:

There was an art installation some years ago near Bath where they "planted" a load of fluorescent tubes in the ground under some electricity pylons / transmission cables, and they were all "magically" illuminated from the current running though the cables passing overhead. Was an interesting piece, science meets art :D

And I’m pretty sure it wasn’t an apocryphal tale that near Wrotham, home to some of the most powerful radio transmitters, it wasn’t unknown to hear radio programmes ‘playing’ in a vacuum cleaner.  I can only guess that the motor windings were being excited by the radio frequencies. 

  • Haha 4

Share this post


Link to post
Share on other sites
Super Wammer
2 minutes ago, Nopiano said:

And I’m pretty sure it wasn’t an apocryphal tale that near Wrotham, home to some of the most powerful radio transmitters, it wasn’t unknown to hear radio programmes ‘playing’ in a vacuum cleaner.  I can only guess that the motor windings were being excited by the radio frequencies. 

Fabulous!

Share this post


Link to post
Share on other sites

Back in my youth I lived near the Brookman's park transmitter. Using a red phone box the Home Service was always in the background.

  • Like 3

Share this post


Link to post
Share on other sites
5 minutes ago, Nopiano said:

And I’m pretty sure it wasn’t an apocryphal tale that near Wrotham, home to some of the most powerful radio transmitters, it wasn’t unknown to hear radio programmes ‘playing’ in a vacuum cleaner.  I can only guess that the motor windings were being excited by the radio frequencies. 

I used to live within a couple of miles of the Wrotham transmitter. I can’t say that I noticed my vacuum cleaner playing the radio; mind you I wasn’t very closely acquainted with my vacuum cleaner...

  • Haha 3

Share this post


Link to post
Share on other sites
3 minutes ago, Camverton said:

I can’t say that I noticed my vacuum cleaner playing the radio

maybe the consumption of some of the local mushrooms would have helped there...

  • Haha 1

Share this post


Link to post
Share on other sites
Super Wammer
16 minutes ago, Camverton said:

 mind you I wasn’t very closely acquainted with my vacuum cleaner...

My daughters reckon my vacuum cleaner spends it time sobbing in the cupboard through loneliness and neglect. 

  • Haha 2

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.