Pertec Interface Cable Length

Grant Taylor cctalk at
Fri Aug 9 23:47:14 CDT 2019

On 8/9/19 10:05 PM, Douglas Taylor via cctech wrote:
> I have a question about cable length - any electrical engineers in the 
> house?

I'm not one.

> 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've heard tell that flat ribbon cables that long don't work for much at 
any speed worth while.

I've also heard tell that you can twist the cable and likely help it to 
the point that it might work.  I'd try for a twist every 1–2 feed.  I'd 
also likely try twisting the cables in the opposite direction.

This opinion comes with a 100% money back guarantee.  100% is opinion, 

It's free to try, and it might work.  So maybe give it a try.

Here's hoping someone else with more information will respond too.

Grant. . . .
unix || die

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