Combatting electromagnetic interference

[choochoo_baloo]

I'm in the midst of laying all the wiring (both power and data) from my garden pier to the house. As per the title, I've been pondering how to feasibly, without being too over-the-top, combat electromagnetic interference (EMI). I know some will say all of this 'worry' is unnecessary, but having spent this much money and effort doing everything else properly, I believe it would be silly to neglect this potential small 'issue'.

These are my thoughts:

• use a lead acid 12V leisure battery as opposed to a *switched* (a linear is beyond my budget!) power supply. This removes any possible electromagnetic radiation from the oscillating (due to the way switching supplies work) voltage along the power cable(s).
• add ferrite chokes to each power AND data cable. I understand that EMI needs to be combated on both the transmitter (power cables) and the receivers (data cables)?

Assuming the above 2 points to be correct, I'd like to ask for guidance on how to select the correct (clip around type) ferrite chokes - how to know the correct resistance rating etc. Also does each cable need a pair - one at each end? I ask because I fear that asking the chap(s) at Maplin may result in waffle/no idea! 

If there is anything I've missed, please let me know! Thanks in advance for any help.

[Dr_Ju_ju]

Before offering any suggestions, what are you thinking that will induce stray signals into what, over what distance ?

Power, including switched mode, may have some residual artefacts, low frequency in the case of linear, or higher frequency for switch-mode. These can usually be significantly reduced by appropriate filtering. Combinations of the above will also reduce any induced interference.

As for data signals, if these are to be mainly USB, then as long as you are using quality cabling, which doesn't attenuate the signals, then there should be no problems, as the signal processors at either end of the link will take of it.

To get cleaner power and signals from my garden pier, I ran mains (armoured cable) to the pier, along with 2 armoured CAT 6 Ethernet cables. I then have a small PC built into a box that does all the movement and camera control. All control is done using remote desktop, and I can get pictures either directly over the second network lead or from the PC for later processing indoors.

But I don't have a separate power supply at the pier, I just use the PC supply (what would normally drive disks) and just power the cameras\mount off this. I've put a scope on the power line to see how 'dirty' they are, and all lines have <1 mV of unwanted signal, and all the gear is happy ...

[kalasinman]

Having an engineer in the family, I understand wanting to do it right. I've dealt with some of these issues in ham radio, and for the trouble of engineering another solution, I'd be inclined to put a battery in . Other thing, the noise produced is a function of the quality of design and duty cycle of the switching PS. My home built VOT speakers ( bi-amped) use switching PS.  My system distortion is under .02 %THD and are speakers are very very quiet.

[choochoo_baloo]

Thanks both for the useful information.

[choochoo_baloo]

Before offering any suggestions, what are you thinking that will induce stray signals into what, over what distance ?

The cabling has a 16m run from pier to study/house.

As for data signals, if these are to be mainly USB, then as long as you are using quality cabling, which doesn't attenuate the signals, then there should be no problems, as the signal processors at either end of the link will take of it.

I was expecting that this would be important, I'll now forgot any ideas of budget USB 2.0 extensions!

Could you recommend a quality brand please - I'm happy to spend the money to get quality data cabling.

Having an engineer in the family, I understand wanting to do it right. I've dealt with some of these issues in ham radio, and for the trouble of engineering another solution, I'd be inclined to put a battery in . Other thing, the noise produced is a function of the quality of design and duty cycle of the switching PS. My home built VOT speakers ( bi-amped) use switching PS.  My system distortion is under .02 %THD and are speakers are very very quiet.

Sorry just to make sure, from your radio experience (with it's loathing of EMI!), you'd say that a leisure battery would be preferable to a decent quality mains switched power supply? 

[kalasinman]

Sorry just to make sure, from your radio experience (with it's loathing of EMI!), you'd say that a leisure battery would be preferable to a decent quality mains switched power supply? 

Clearly the battery is 100% certain. In practice, it may be the difference between having an elephant step on your foot or a rhino

[Dr_Ju_ju]

Sorry ChooChoo, but at 16 meters that is far too long for USB to reliably work, even with the best cables.  You're into using powered USB repeaters, which I have found to be rather hit & miss.

it may be better to run a Cat5e network cable (armoured & screened e.g. http://www.ebay.co.uk/itm/331166578836?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT )   & then use a USB\Network hub e.g. http://www.maplin.co.uk/p/gigabit-network-server-4-port-usb-20-hub-n01jz

The down side to this, is that you would need to crimp your own connectors onto the cable, which you may be uncomfortable with