RE: Andy's UPS - EM Interference ? Should I move things ?

["Nigel Giddings" <nigel@xxxxxxxxxxxxxx>]

Gareth,



I would be surprised if you are getting interference from the UPS. I see
the Compaq R3000 mentioned in another post, I have two of these rack
mounted and never had an issue, also several other UPS as well, again
they don't seem to be a source of any problem.



If I had to suggest an area that may be the cause I would suggest earth
loops which will give a 50Hz hum on any signal wire affected.



How well have you earthed your racks? Have you run all your earths back
to a central earth point (ie not looped from one piece to another).
Small voltage differences (Potential Differences) can occur on earthing
systems and when you run another cable between those two points you can
end up carrying noisy earths along them.



Not sure what is suffering interference, HDMI over CAT5e? Usually earth
loops can be heard on analogue systems as mains hum low frequency 50Hz.
Using HDMI, a digital system, you won't be able to hear that...



Of course the other issue is inductance; CAT5e should reject that as
long as you have kept all the pairs as pairs. The twisting of the pairs
within the cable help reject (balance out) the interference. If you send
signals using odd wires, not pairs, you lose the effect of the twisted
pairs and can pick up noise. Again it will usually be mains related and
be at 50Hz. This is typically caused by running parallel with mains
cables that carry high current. Having said that I can recreate this
problem on a kitchen lighting circuit carrying only a few 100 watts.



Some food for thought.



Nigel



-----Original Message-----
From: ukha_d@xxxxxxx [mailto:ukha_d@xxxxxxx] On Behalf
Of Gareth Cook
Sent: 18 July 2008 07:28
To: ukha_d@xxxxxxx
Subject: [ukha_d] Andy's UPS - EM Interference ? Should I move things ?



Having some issues with signals, and I'm wondering if the massive UPS
should be avoided - it lives in the bottom of the rack, and then the Sky

box and other gubbins right above it.

Is the UPS a good source of interference for signals ? Like to gather
some
thoughts before spending hours re-jigging anything !

tia

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