Pertec Interface Cable Length

Dave Wade dave.g4ugm at
Sat Aug 10 03:57:18 CDT 2019

> -----Original Message-----
> From: cctech <cctech-bounces at> On Behalf Of Douglas Taylor
> via cctech
> Sent: 10 August 2019 05:06
> To: General Discussion: On-Topic Posts <cctech at>
> Subject: Pertec Interface Cable Length
> I have a question about cable length - any electrical engineers in the house?

Its electronics, rather than electrical engineering. Electrical Engineering is power distribution.

> 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.

So the hardware is good.

> 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 can't see 5 foot being too long for data from a tape, the data rates aren't huge. At most you have added 10ns to the delay times.
On the other hand I have been wrong in the past and could be wrong again..

I assume you have checked the cables. Ribbon cables are prone to come loose from the IDC pins if it’s a IDC connector, and if soldered can break.... 

> Doug


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