linuxaudio.org

On Tue, Jan 18, 2011 at 10:59:59PM +0100, Jörn Nettingsmeier wrote:
> * source

quoted text
> * 5m or so of suitable cable

> * bnc wall socket

> * 20m installation cable (-63dB/100m @ 3ghz)

> * a ghielmetti patchbay (which includes two canare contacts to the

> patch cord and two bnc on the rear, unfortunately)

> * another 20m installation cable

> * bnc wall socket

> * another 5m cable

> * sink

>

> question 1: any hopes for reliable hd-sdi?

Can't really answer this. But BNC seems to be the standard

connector for this, so it's probably OK.
> question 2: how can it be that a kick-ass company like ghielmetti

quoted text
> does not offer video patchbays that allow direct connection of coax

> installation cables, but require rear bnc connections instead?

This is probably just a question of being practical. Wiring up

a patch bay to things outside the rack (or the equipment it is

part of) without connectors leaves you with something that is more

or less cast in stone. It can also be quite difficult to install.

I recently wired up a 96 point audio patchbay without rear

connectors (i.e. soldered), with almost all of the connections

going outside. Luckily these cables had the other end free and

didn't go into some wall. But I'll avoid to do that again...

I doing another one these days (the Sala dei Concerti - you know

the system needs some rewiring :-) but this time the patchbay has

rear connectors - it would be near impossible get it wired up

otherwise.
> question 2b: is there an alternative for direct rear coax

quoted text
> connection, thereby cutting out two potentially disruptive contact

> surfaces?

Haven't seen it. When I was working at Alcatel, all HF racks we

constructed had back panels with double through-panel BNCs for

external connections. No external cable would ever be attached

directly to any of the equipment inside the rack. And more often

than not, the same through-panel BNCs were used on the actual

equipment boxes themselves, with an internal BNC-SMA cable to

connect to the PCBs. So any signal going in or out would pass

via at least 4 BNCs, and 4 again if routed to another rack.

I often worried about this (since we mostly did equipment doing

very precise phase measurements etc.), but the HF 'old hands'

told me each time that I shouldn't.
For really critical stuff at 2 GHz and above they would prefer

SMA, and if things were really extreme the coax cables would

be replaced by rigid tubes, welded to the SMA connectors using

special HF induction welding equipment. SMA handles much higher

frequencies than BNC, but I don't think it matters for SDI.
> question 3: i'm thinking of getting neutrik isolated bnc connectors

quoted text
> (the d-type ones that are semi-recessed and thus well protected from

> clumsy passers-by). but their soldering lugs break the coaxial

> structure - cause for concern?

That could well be cause for concern. Is there really any advantage

to recessed BNCs ? The connector itself is usually solid enough,

and once a cable is attached to it the Neutriks are as vulnerable

as any other.
> question 4: do i really want to solder hf stuff (even though the

quoted text
> voltages are not too high), or will it unsolder itself eventually?

> any recommendations as to procedures and tin?

Unsolder itself ?

Most BNCs today are crimped rather than soldered. If done using

the correct tools and procedure this should actually be better.
Ciao,
--

FA
There are three of them, and Alleline.
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