On Tuesday, January 18, 2011 09:40:50 pm firstname.lastname@example.org did opine:
Hello Fons ;-)
> On Tue, Jan 18, 2011 at 10:59:59PM +0100, J�rn Nettingsmeier wrote:
Which is several reflections and a lot of vswr in a 75 ohm video circuit.
Why? Unless special ordered, the bnc connector you can by in 20 pound
bags, is a 50 ohm connector, and every one encountered in a 75 ohm video
circuit sticks up like a pocket combs teeth on a TDR.
The down side is that while there are 75 ohm bnc available, there is no
provision to prevent someone from plugged a 50 ohm connector into that 75
ohm socket. The 50 pin is too big for the 75 ohm socket and breaks the
female socket, expanding it so that a proper 75 ohm connector will likely
not even make a connection when its locked on. Here in the states, after
encountering lots of that sort of damaged sockets, I did find a src of 75
ohm bnc's but then had to go round up the right sized numbered drill bit
and a pin vice to spin it with, and drill out the back end of the pin in
order to get my fav 75 ohm video cables center conductor into the pin for
Needless to say that makes for about 4x the time in installing the
My fav cable is Susan Clarks (Clark Wire & Cable) type 7559, its quad
shielded with both a silver plated 90% or so braid over a metalized mylar
wrap on the foam core for s shielding effectiveness of about 110 db, and
with its foam core, its both low loss and very very flexible.
> > question 1: any hopes for reliable hd-sdi?
And as long as its not what we here in the US call a 'Cambridge' connector,
which is a solderless install, you special strip the coax and literally
screw the connector onto the end of the cable. But its a time bomb whose
fuse could be as little as a couple of months long when install on a soft
foam cored cable. The cable cold flows and collapses away from the
connector shell and you have a very poor shield connection and crosstalk
you can see at the other end of the cable when there are 40 such cables
bound in a truck going 10 meters to another rack.
> > question 2: how can it be that a kick-ass company like ghielmetti
As long as the cable lengths were matched, shrug.
> For really critical stuff at 2 GHz and above they would prefer
The secret is achieving a 'gas-tight' crimp. Not having the correct
crimping tool to do that leaves you with a time bomb with a years long
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