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16 channel digital probe for HP54645D MSO?

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carl_lab:
What do you think, do I need the original woven ribbon cable?
What about bandwidth?

Could this cable be a reasonable compromise ($1.85/ft = $6.10/m)?
http://www.surplussales.com/wire-cable/ribbon.html
http://www.surplussales.com/wire-cable/pdf/wrc-468-2829-050.pdf

georgd:

--- Quote from: carl_lab on September 29, 2016, 07:48:17 am ---What do you think, do I need the original woven ribbon cable?

--- End quote ---

Patent paper with best description what is it an why need to use:

https://www.google.ch/patents/US4777326

Quote from the patent:
A type of cabling method used in the prior art required the use of a coaxial cable with a resistive center conductor for each signal to be probed. For example, a logic analyzer having 16 probes would require 16 coaxial cables tied together from the logic analyzer to the system under test. This tended to greatly improve the performance of the probing system, since the shielding was greatly improved, bandwidth was increased, and crosstalk was reduced. However, the result was an extremely bulky, costly, and heavy cable, making it difficult for the user to operate with a typical system under test.

On short distances up to 20 cm and on frequencies below 100 MHz an ordinary flat cable should to work.

Georg
Georg

JFJ:

--- Quote from: carl_lab on September 28, 2016, 07:29:29 am ---I thought the original was a woven/twisted pair type flat cable?

--- End quote ---
The original cable is woven, but its signal and ground conductors are not in twisted pairs. Each signal conductor is separated by two, thinner, ground conductors. This parallel signal/ground conductor arrangement is intended to reduce the capacitive coupling between adjacent channels, to avoid crosstalk. Flat, 80-conductor, Ultra DMA hard drive cables used a similar technique to reduce crosstalk.

A twisted pair cable would be of no benefit, because your scope's digital inputs are single ended (all the signal grounds are common). A differential input would be required to reject the common noise pickup of a twisted pair.


--- Quote from: carl_lab on September 28, 2016, 07:29:29 am ---Pod 1 Data + J Clock,
Pod 2 Data + K Clock,
Pod 3 Data + L Clock,
Pod 4 Data + M Clock,
Pod 5 Data + N Clock or
Pod 6 Data + P Clock Logic Analyzer Probe?

What's the differences?

--- End quote ---
When purchased new, the pod connectors are all the same (unlabeled). A sheet of self adhesive labels is included, so that the user can assign each pod's function.

carl_lab:
Thanks georgd and JFJ.


--- Quote from: JFJ on September 29, 2016, 11:37:01 am ---A twisted pair cable would be of no benefit, because your scope's digital inputs are single ended (all the signal grounds are common). A differential input would be required to reject the common noise pickup of a twisted pair.

--- End quote ---
I think, this is correct, but regardless there are twisted pair P-ATA/UDMA HDD cables:



AFAIK P-ATA/UDMA is single ended, unlike differential SCPI, so why they use twisted pair cable for P-ATA/UDMA then?




timb:

--- Quote from: carl_lab on September 29, 2016, 04:58:24 pm ---Thanks georgd and JFJ.


--- Quote from: JFJ on September 29, 2016, 11:37:01 am ---A twisted pair cable would be of no benefit, because your scope's digital inputs are single ended (all the signal grounds are common). A differential input would be required to reject the common noise pickup of a twisted pair.

--- End quote ---
I think, this is correct, but regardless there are twisted pair P-ATA/UDMA HDD cables:



AFAIK P-ATA/UDMA is single ended, unlike differential SCPI, so why they use twisted pair cable for P-ATA/UDMA then?

--- End quote ---

Because, it's easier to route these cables inside a computer case, makes things look overall neater and helps with cooling. This happened in the late-90's/early-2000's.

Originally, 80 conductor (P)ATA-66 cables were flat, just like their slower 40 conductor ATA-33  counterparts. Case modders would take Exacto knives and cut little slits between every few conductors and then zip tie them together. This led to "round" cables being commercially produced; they're not actually twisted pair in the true sense (though the entire bundle may be twisted together).

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