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Thread: DIY SDI Cables

  1. #1
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    Default DIY SDI Cables

    Folks,

    Ok, now with some excellent SDI drives and a working KDA50, we need some SDI cables. I usually make all my own cables, but SDI cables are going to be tricky.

    The only ones I have for reference are the pigtails that come out of the back of the RA80. After some reasearch and study they are an arrangement of four 93 ohm coaxes side-by-side as a ribbon. The cable ends are 8 pin female berg-like connectors. Four pins are the center conductors and the other four are the corresponding shields. I'm thinking if I could find tiny 93 ohm coax (like RG-174, but 93 ohm, not 50) I could make my own. No such luck finding tiny 93 ohm stuff though.

    Any thoughts?

    Lou

  2. #2
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    Default

    Interesting findings so far:

    The US patent for the SDI cable assembly is number 4596432. The connectors are 4040704 and the ribbon coax cable is 3775552, as referenced in the cable assembly patent. All assigned to AMP.

    The crimp tool for the conectors is described on AMP instruction sheet IS9071. The sheet for the connectors was IS2577. The 8 pin connector was AMP part no. 226733-1. The 32 pin for the KDA/UDA50 would be 1-226733-4 (actually this connector accomodates 14-17 coaxes and has 34 pins, it looks like there is no connector for 16 coaxes). The 4-coax cable itself was part number 226464-4, the 16 was 1-226464-6. I was able to download the IS sheets and the cable spec drawing from the AMP website. Unfortunately, all pieces/cables are obselete.

    We're still looking for some miniature 93 ohm coax. Cutting up existing SDI cables might be tough. The AMP spec says it has #30 center conductors and #30 drains. These are only 0.010" diameter and would be very fragile.

    Lou
    Last edited by Lou - N2MIY; November 10th, 2009 at 08:43 PM.

  3. #3

    Default Coax - think the impedance is critical?

    Lou,

    Have you tried wire-wrap

    I wonder if the impedance is really that critical. I got some 75 ohm super-thin coax at the aforementioned Skycraft parts. There are also impedance matching tricks from the Ham Radio bag-of-tricks as you well know.

    I'm all for doing it right, and may be speaking out of turn, but do you think you could get it connected first then worry about exact specifications later?

    -Crawford

  4. #4
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    Crawford,

    Actually, I found some miniature 93 ohm coax online (http://www.texcal.us/coaxial-cable/93ohm1.html), but didn't ask for a quote yet. It looks like the minimum order quantity is 25', which seems reasonable. The smallest stuff is 0.130" OD, with a 0.011" dia. center conductor. Of course, the ribbon coax was on 0.100" centers. The 0.130" stuff is at least a lot more manageable than RG62, which is closer to 1/4" OD.

    So, since it won't be hard to get the cable impedance right, we will try that.

    You know though, I'd bet that the impedance is not that important. I say this because the cable is terminated in such a barbaric way for coax (going to a berg connector). Who knows what the impedance of that connector is. The result must be lossy and cause reflections.

    Lou

  5. #5
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    Default Home Made SDI cable is working!

    Folks,

    It looks like I have successfully made my own SDI cable to go from the KDA50 boardset to an SDI disk drive.

    Total material cost was under $3 USD for a four foot cable. For the connectors on the ends, I used Jameco 157462 housings (and the corresponding female crimp pins). This housing is actually a 40 pin housing (but they are cheap, so I cut them down to the number of pins needed with a single edge razor blade.)

    The mini coax was 75 ohm scavenged from broken VGA monitor cables. I was going to buy proper 93 ohm mini coax, but the cheap ham in me wanted to try the cables from the trash first. For some reason I have been cutting the cords off of broken VGA monitors and saving them over the past few years. I'm glad I did.

    I discussed the impedance mismatch with my father, and he thought that the data rate was sufficiently slow that I shouldn't worry, and given the fact that proper cables used to be >50 feet long and that mine was only four, I should give it a try.

    So, I have a KDA50 in my 11/73, connected to an RA72 drive. It's sitting next to me, and has been running the ZUDJ** diagnostic for the last 45 minutes. No errors yet!!

    The four coaxes must be kept elecrically isolated. I crimped pins to the center conductors and to the shields (followed up with a little solder. This would not normally be required with these crimp pins, but in this case, the center conductor is very small and was not fully crimped tightly.) I had to insulate each of the stripped back shields with shrink wrap. By the time I was finishing the cable, I was getting pretty good. The whole job took about an hour and a half. Tools required were single edge razor blade, good wire cutters / strippers, soldering iron, shrink tubing, and lastly a good pin crimper (I have an AMP).

    Pictures here:

    http://www.vintage-computer.com/vcfo...php?albumid=53

    Lou
    Last edited by Lou - N2MIY; December 13th, 2009 at 08:56 AM. Reason: typo

  6. #6

    Default

    Cool!

    That is a neat setup

    Would you say that your RA-disk make a lot of noise? I would describe mine as making a whiny noise, do you recognise that?
    Looking for: anything from SGI or DEC/digital
    Pictures of my collection: www.pdp8.se

  7. #7
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    Pontus,

    The RA72 does seem a bit noisier than say, the RD31s that I am used to. It seems that the sound of the head moving when seeking is the most notable. Of course, the drive is sitting out in the open on the table at the moment.

    I will say this though - it is FAST!!! I'm running RT-11 and it's must faster from the RA72 than the RD31 or 32. I wonder what would be faster SCSI (can't affort it) or SDI (have it)?

    My dilemma now is with having two MSCP disk controllers in the same machine. Perhaps I should start a new thread on that and how to deal with HUGE disks under RT-11. All I have is RT11 V5.3, which supports 8 partitons per handler, with 32MB per partiton. So one handler will allow access to 256MB or one-fourth of my huge 1GB RA72. Yeah, this needs a new thread...

    Lou

  8. #8

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    Quote Originally Posted by Lou - N2MIY
    I will say this though - it is FAST!!! I'm running RT-11 and it's must faster from the RA72 than the RD31 or 32. I wonder what would be faster SCSI (can't affort it) or SDI (have it)?

    My dilemma now is with having two MSCP disk controllers in the same machine. Perhaps I should start a new thread on that and how to deal with HUGE disks under RT-11. All I have is RT11 V5.3, which supports 8 partitons per handler, with 32MB per partiton. So one handler will allow access to 256MB or one-fourth of my huge 1GB RA72. Yeah, this needs a new thread...
    I ran RT-11 for awhile on my old 11/34 more as just a test. I no longer have the RL02 pack as I gave it to someone. Why two MSCP controllers? I have a SCSI card but do not have
    a matching 11/23 to do a comparison test. HUGE disks under RT-11? Isn't that an Oxymoron?

  9. #9
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    Tim,

    The two MSCP controllers in the system are the RQDX3 (for floppy support, and I have two MFM drives connected) and the KDA50. I figure I at least need floppy support for moving files.

    I currently have the RQDX3 at the normal CSR/Vector for MSCP controllers 172150/154. I put the KDA50 at the usual secondary controller address (160334 and arbitrartily chose open vector 140).

    I sysgened RT-11 V5.3 XM for two MSCP controller support. So DU0: through DU3: are the floppy and MFM drives, and DU4: through DU7: are the first four partitons on the RA72.

    I had success under the FB monitor copying and renaming the DU handler, then doing SET DA CSR=..... So, under FB, I have DU0: - DU4: the floppies and MFM drives, then DA0A7: and DB0B7: etc. for all the partitions on the RA72. It's pretty crazy, the 1 GB RA72 is thirty-two RT-11 partitons. I would agree -HUGE disks on RT-11 is an oxymoron.

    This did not work under the XM monitor though. I couldn't get copies of the DUX handler to work the same way as DU.SYS did under FB. More troubleshooting required there.

    Under the XM monitor though, the RA72 is bootable. As I wrote before RT-11 is fast on an 11/73 when run from a fast disk.

    I'm not quite sure what to do with all this space yet.

    Lou

  10. #10
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    Default New Approach to Home Made SDI Cables

    I'm not sure why I didn't try this earlier!!!! Since the mini coax in real dec SDI cables is 93 ohms impedance AND it actually appears to be used in a balanced circuit, I decided to try CAT5 UTP ethernet cable, where each pair has an impedance of about 100 ohms.

    Guess what, it works fine and is a lot easier to work with then the tiny coax!!!!

    I made a 35 foot long cable and put crimp pin type header connectors on both ends. Exactly the same connectors I used with the coax-based cable. I left the cable as a coiled mess mingled amongst various power cables behind my 19" racks. The controller end was in the UDA50 that I have just added to the 11/04, and the other was in an RA72 drive. No errors - it works fine!!

    My next experiment will be to add interposing RJ45 faceplate sockets and another length of consumer CAT5 ethernet cable with RJ45 plugs. If this works, no more long SDI cables - I will make a breakout cable for the controllers from the 32 pin plug to four RJ45 female faceplate sockets. Then for the drives, a similar faceplate with two sockets (since the drives are dual ported.) Then consumer CAT5 cables in between.

    Lou

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