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Musing in the eye of Hurricane PaulSurround
2017-09-02, 12:43
Post: #11
RE: Musing in the eye of Hurricane Paul
(2017-09-02 11:45)Briain Wrote:  Packet drops would require quite a large signal to be coupled into the cat5, so I doubt that's what's happening. If packet re-sends were to create any audible impact, then the easiest way to test for that would be to heavily load the network segment up with traffic (thus causing a few collisions and re-sends) and see if it changes the sound of the DS streaming. As I say, I doubt that's what's happening and in any case, that would be masked by the DS's data buffer, so by [thought] process of elimination, it leaves only what's sometimes referred to as the 'pin 1 problem' (though in this case, via the Ethernet socket). Google will find many articles on same (including radio ham microphone cables) and when I just tried it, the first link it found was on the Rane site (see here: http://www.rane.com/note165.html) which I haven't read, but a quick scroll down the page indicated it could be quite a good one for describing what's going on. Of course, an Ethernet cable doesn't typically have a screen (which terminates to the board instead of the case) so it's not exactly as described on that page, but it is 4 unscreened pairs extending into the case and terminated on the Ethernet chip (so more like 4 pin one problems Tongue ) and though I assume that Linn (and the Ethernet chip designer) have taken measures to deal with that possibility, I can only assume that once inside, a tiny fraction of it is being perhaps coupled into areas beyond that interface (as unless I'm missing something very esoteric about it all, I really can't think of any other mechanism whereby patch cables - or the screening thereof - could make an audible difference). Of course, I would be happy to be proved wrong, as the answer would be even more fascinating than a variant on the 'pin 1 problem'! Smile

Waving a radio about is quite interesting. The thing I like about the bank of FRIWO units is that they're quiet close up, but once you get a few feet from them, they are pretty much undetectable (I was using a nice old Roberts Radio for the test). Smile

The Sky+ box was a real racket producing horror, but I'm not sure if they're all like that, or whether my one has lost part of its mains filter (that can happen with SMPS units, be they the ones inside products, or of the wall-wart variety). I know that one of my friends has a selection of Sky boxes (he keeps them for helping out when a customer's one fails) so I must borrow one of the same type and see if it's similarly noisy.

It would be handy to identify a tight-braid coax (that you can buy by the metre, on line) as the stuff I used was a bespoke one used for the IF of NEC microwave radio units (similar arrangement to the coaxial link between a sky box and the LNB) and it has twin screens with almost no gaps between the wire strands (though for this sort of stuff, I think almost any grade of screen would more than suffice).

To cover it, I used something like the RS stuff (http://uk.rs-online.com/web/p/cable-sleeves/0408237/) and a short length of clear heat-shrink at each end (to keep it in place and stop it from fraying).

When I looked at the Sky+ box, I discovered that the case is grounded through the HDMI connection to my ADSM, so I terminated the box end of screen with a lug and fitted it under one of the existing screws at the back (so effectively 'extending' the Sky+ box's chassis to also surround its mains cable). Once you remove all the plastic, the Sky+ box is actually quite nicely screened by an internal metal box (only the back of which is left visible).

Bri

PS Poking the short wave radio at the front of the DS display window is rather fun (remember that you have to rotate it as the radio's internal ferrite rod antenna is directional) as you then hear the (actually quite funky) sounds from the digital works within. It's actually quite a musical cacophony, but I guess you would expect nothing less from a KDS! Big Grin

Facinating stuff Briain.

I'll do some more experiments when I get home. Big Grin

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RE: Musing in the eye of Hurricane Paul - Paulssurround - 2017-09-02 12:43

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