Fiber terminations -- UPC vs APC

Mon Nov 19 22:30:41 UTC 2012

On Nov 19, 2012, at 4:37 PM, Jeff Kell wrote:

> Looking for some guidance/references on the use of UPC versus APC  
> terminations on fiber
> cabling.  Traditionally we have done all of our fiber plant  
> targeting data usage with
> UPC connectors.  We are also looking at proposals for fiber  
> distribution plant for
> video, and the possibility of using some of the existing fiber plant  
> for that purpose;
> as well as any new fiber plant that gets installed for video  
> potentially as data.
>
> The video folks are set, determined, and insistent that they need  
> APC terminations.

APC is pretty much the standard for high-power video distribution, and  
for very good reasons.  The return loss is much better for APC than  
for UPC, for instance, and that can be very significant depending upon  
the equipment being used to drive.  Much video distribution gear,  
including passive splitters and EDFA's, are only available with APC  
connectors.

Mating an APC to a UPC will result in an 'air-gap attenuator' being  
created, and that may be a problem.  A significant problem for some  
gear, in fact.

Really high-power long-haul gear may need APC as well, even for  
networking stuff.

Your choice boils down to parallel plants or only APC with UPC jumpers  
for non-APC equipment.  You really really don't want to have any UPC  
connectors in a really high-power path that needs APC all the way; I  
have actually seen some warranty statements, for some older equipment,  
primarily EDFA modules, that indicate that the warranty would be  
voided if any non-APC connectors were in the path anywhere.  The  
reflections from a UPC end can detune some of these lasers, and can,  
in theory at least, cause permanent transmitter damage that won't be  
under warranty.

You could, though, provision half APC and half UPC, since the color  
coding is pretty clear.  You can even use, say, all LC on your UPC  
patches and all SC on you APC patches or similar, and get both with  
little danger of intermating.  I think I'd personally rather just  
provision all APC in the backbone fiber runs and install APC to UPC  
distribution runs to your network gear.

But you'll have to train people to always plug green connectors into  
green connectors, and blue into blue, and never should green and blue  
mix.