Pertec Interface Cable Length

[Jon Elson]

On 08/09/2019 11:05 PM, Douglas Taylor via cctech wrote:
> I have a question about cable length - any electrical 
> engineers in the house?
>
> Connected a Qualstar 1260 tape drive to an Emulex TC02 
> qbus tape controller in a pdp-11/53.  The interface is 
> pertec with 2 50 pin cables.
>
> When I use a pair of short flat ribbon cables, 18 and 30 
> inches each, it works.  Under RT11 I can INIT, Copy, DUMP, 
> do a Directory.
>
> It doesn't work when I use a pair of 5 foot long flat 
> ribbon cables.  Are they too long?  Do I need twisted pair 
> type of cable?  Is it possibly a termination problem?
>
I have used cables about 20 feet long without trouble.  The 
2 50-pin cables is the Pertec formatted interface, which is 
really forgiving.  Does you drive have terminators in both 
ends of the cable (both at the TC02 end and the drive end)?
Now, I will mention that I have ONLY used twisted-pair 
ribbon cables with both flavors of interface, never straight 
ribbon cable.

Jon