[QuadList] Patch cables/bays (Was ...some useful info from BAVC...)

[Ted Langdell]

Hi, Ed,

Glad you found the links useful.

On Jul 12, 2009, at 10:25 PM, COURYHOUSE at aol.com wrote:

> Seeing one photograph of  racks reminds me...  I have the rack part  
> of the video patch bay but do not have any cables to plug in!  It  
> would be nice to set everything up this way...  does anyone have any  
> extras?


You may be easily able to tell what you have by looking at the side of  
the jacks and then Google the part numbers.  Do that first before  
jamming a patch cord in one.  The wrong size will either not fit or  
cause damage.

This ADC document http://www.adc.com/us/en/Library/Literature/106085AE.pdf
explains the differences and the damage that can be caused to an RCA  
style jack if you try using a WECO (Western Electric) style patch cord.

So, you need to know whether your panel has:

WECO or RCA
75 ohm or 50 ohm (You need 75 for video)
Terminating or non-terminating
Normaled or single jack "straight-through"

It might have a mix of patch styles.  Look closely for part numbers,  
and if necessary carefully remove the jacks from the panel to  
investigate.

Aside from the physical differences, the ADC doc. outlines some  
problems using standard WECO jacks and patch cords with Serial Digital  
signals.

ADC has a special patch cable that allows use of existing WECO jacks  
with SDI signals without  an impedance problem leading to excessive  
bit error rates.

Like water flowing downhill, patch bays are usually set up so that if  
you have—say— the output of a VTR intended to go to a switcher input,  
the source output goes to the top jack and the destination input is  
fed from the lower jack, right underneath.

This allows the use of "patch plugs" to direct the signal if "Straight  
Through" jacks are used in the jack field.

A straight-through jack requires a patch cable to work. It may be  
terminating (adds a 75 ohm resistor across the circuit when there is  
no patch cord inserted) or non-terminating, which requires a  
termination at the patch bay if the circuit is active.

A "Normaled" jack allows video from the rear upper jack connection to  
flow through to the rear lower jack connection without a patch cable  
in place.  Most patch bays I've run into are "normaled."

It makes life a lot easier and requires the use of a patch only if  
there's something un-usual going on.  Say, patching around a bad  
device, or sending a source to a destination that's not available  
without the patch.

Hope this is helpful.

Ted


Ted Langdell
Secretary
Skype: 	TedLangdell
e-mail:	ted at quadvideotapegroup.com

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