Re: [LAD] [OT] 3ghz coax and soldering...

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

> * source
> * 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
> 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
> 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
> (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
> 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.
_______________________________________________
Linux-audio-dev mailing list
Linux-audio-dev@email-addr-hidden
http://lists.linuxaudio.org/listinfo/linux-audio-dev