Compact connector (and cable) for screened 50 ohm diff pair.

[Nial Stewart]

I'm looking for a connector which mounts on a board in a PC104+
stack and am stumped. I need something which meets the following
requirements,

PCB mounted header <13mm high, and associated cable connector.

Terminates screened cable suitable for 50 ohm diff pair.

Reasonably compact, I only have one diff-pair per header.

Reasonably robust, used in an industrial environment, but by professionals.


BTW, it's feeding an ADC which is sampling at 200Msps so I don't
need a bandwidth of GHz.

All the requirements spec states is...
"The ADC differential inputs are connected via 33R series resistors
(at the chip) direct to a miniature shielded input connector"

The other end of the cable doesn't exist yet, my contact mentioned
tri-ax cables but these don't seem to fit in the space I've got.

I suggested something like an HDMI or mini USB connector but
they've come back saying they want a "generic non-specific" connector.


I'm stalled on this so any suggestions are very welcome.



Nial.

 

[Nial Stewart]

In situations like this, my policy is "make it their problem." Tell

them to decide on a connector and cabling system, with all part
numbers and assembly directions. When they don't do that, and are out
of time, you can tell them what to do. I'd suggest something standard
and cheap, USB or SATA maybe, so you can just buy cables.

That's what I thought, but they want non application specific
solution!

I think I might put a bit of effort into talking them round here,
something like this is probably the best solution.

The 33R is a little weird. You'll need to terminate at the actual
cable differential impedance on your end.

There's provision for 50 ohms between the pair at the ADC (not fitted).

I don't know if they want to experiment here, I'm just following the spec.

You could use edge-launch SMBs and two RG174 cables, but a standard
diff cable would be easier.
It's surprising how well "make it their problem" usually works, in all
sorts of situations.

As someone said, things would be great if it wasn't for clients (and
employees).


Thanks for the feedback John, that's another pint I owe you (proper
UK pint, ie 568ml)!


Nial.

 

[Nial Stewart]

If it would be indelicate for you to tell them that they're idiots, I

could do it for you.

He who pays the piper doesn't get called an idiot.


They are worked on slowly so they decide that it's their idea in the first
place.





Nial.

 

[Nemo]

I'm looking for a connector which mounts on a board in a PC104+

stack and am stumped. I need something which meets the following
requirements,

PCB mounted header <13mm high, and associated cable connector.

Terminates screened cable suitable for 50 ohm diff pair.

Reasonably compact, I only have one diff-pair per header.

Reasonably robust, used in an industrial environment, but by professionals.

How about a... stereo audio jack? And for the cable, screened twisted
pair?

(Though I've read in this NG, and other places that twisted pair's
fields extend outside the cable, the implication being you should not
use it near lots of metal objects.)

Such a cheap connector might not meet the following requirement:

BTW, it's feeding an ADC which is sampling at 200Msps so I don't
need a bandwidth of GHz.

But if they are asking for 33 ohm resistors, instead of... what is it...
two 37.5 ohms normally? perhaps they're not too worried about ideal
terminations.

All the requirements spec states is...
"The ADC differential inputs are connected via 33R series resistors
(at the chip) direct to a miniature shielded input connector"

The other end of the cable doesn't exist yet, my contact mentioned
tri-ax cables but these don't seem to fit in the space I've got.

It sounds like they have partial knowledge of the subject, or have not
had time to think through the entire system, and are in a
blame-avoidance culture and want you to tell them what will work.

 

[Nial Stewart]

I'm stalled on this so any suggestions are very welcome.

You might look at a mixed signal D connector - the standard "sub-
minature" D-connector shells accomodate coaxial inserts, very silimar
to SMB connectors. Farnell stock the Harting range

You will have to poke around the web-side to find the dimensioned
drawings of the D-connector shells, but they are there, and it looks
as if they ought to fi tinside the space you've got.

Thanks Bill,

That looks like another possible solution, I'll look into it.


Nial.

 

[Nial Stewart]

Careful: the coax-insert D-subs are very expensive.

The client has said he's past experience with these and doesn't like them,
he thinks they aren't reliable enough.

At 200 MHz, a regular d-sub would work, but you'd probably have to
make your own cables.

USB or SATA are the way to go. Or even shielded CAT5 and RJ45
connectors.

Most RJ45 sockets are tight height wise but I agree with USB / SATA.

I'm working on them.


Nial.