Home-made SDI cables
Lou
I am interested in making my own SDI cables. I have a KDA50 and
an RA80, 72, and 73. All I have are the SDI cables that came on the
RA80.
I checked the prints very carefully at the RA80 end and KDA50
end, and noted that I could plug the SDI cable coming from the back of
the RA80 directly into the KDA50 (after I took the large metal shell
off the connector.) I did this, and it works.
This is a kludge though, and I really want to connect the RA72.
I have no other cables, and don't want to spend big $$$ to get the
proper four-way KDA50 cable from a dealer.
I studied the SDI cable, and did a little research. The cable is
ribbon coax, with four 93 ohm coaxes. At the AMP female plugs on the
end, the center conductors all go to the odd number pins, and the
corresponding shields to the evens. Is there a 93 ohm small coax (like
RG-174, but 93 ohms instead of 50)? I think I could crimp female berg
connector pins to the center and shields and basically make my own
cable. Has anyone done this?
I thought about buying a 25 foot cable off e-bay and cutting it
up for the coax. However, upon close inspection of the cables on my
RA80, the center conductor and shield of the ribbon coax look very
very small, too small to crimp pins on to.
Any advice is appreciated.
Lou
Tim Radde
So the RA80 is working again? Great. I have no suggestions on how to
make these, but if you figure out
how let me know. I could use some more of them.
Tim
Jörg Hoppe
I have exactly the same problem.
I did a lot of soldering and found the cable to very critical.
For instance, I made very short (10 cm) rats-nets adapter to connect the
red SDI cable to my RA81. This worked only if I seperated the 8 wires
physically. If they run in parallel by accident, even on this short
distance, there are transimssion errors.
Tests with a CAT5e ethernet cable failed too.
Good to know what kind of coax is right, thanks to your research.
I found the external SDI cable part number is "BC26V".
ebay.com has several sellers for "DEC BC26V", at low prices ($17-$20).
I surely will buy one or two of those, if I have time for my RA81 again.
regards
Joerg
Lou schrieb:
H Vlems
Instead of RG58 you could try IBM coax that was used IIRC to connect
3270 terminals (not the twinax cable used on AS400's).
That cable, RG60 or RG62 had an impedance of more that 90 ohms. That
might work for you.
Hans
Lou
RG62, although 93 ohms, is a bit large on the OD. I have found an
outfit in California that has miniature 93 ohm coax (TexCal Wire and
Cable). Their smallest is 0.130" OD. The center conductor is pretty
small, 0.011" OD. This seems like a reasonable size to try, about 1/2
the diameter of RG62.
I actually found some very interesting documentation on the SDI cables
for anyone interested. Not extremely helpful though, except to confirm
my suspicions that the original cable and connectors would be hard to
work with unless one had proper tooling.
US patent 4596432 covers the cable assembly. 3775552 is for the cable
and 4040704 is for the connectors. These are all assigned to AMP.
The cable appears to be AMP p/n 226464-4 (for the four coax version.)
The AMP website actually has available for download the specification
drawing, complete with capicitance (14pF/ft), attenuation, crosstalk,
propagation delay (for velocity factor), etc. However, the cable is no
longer made.
The connectors appear to be detailed on AMP instruction sheet IS2577,
also on the AMP website. From there, one can determine the exact part
number of the connectors (the 4 coax plug on the disk drive end is AMP
p/n 226733-1), see the outline drawing, etc. Again sadly, none of this
is still made.
From the assembly instructions, these would not be easy to make up
without proper tooling. Stripping the cable must have been done with a
thermal gang stripper (so as not to damage the #30 center conductor
and shield drain. Then, a really expensive looking bench mounted
crimper crimps the whole affair together.
I may buy a 25' length of the miniature coax and some plain vanilla
AMPMODU housings and contacts. The trick will be crimping contacts
onto the 0.011" center conductor. Fortunately, I do have a nice AMP
crimper for those pins (but never tried anything so small before.)
I'll report back in a few weeks (so long as the coax does not break
the bank.)
Lou
John Wallace
This may be a daft idea, or may be sensible but already considered
quietly and rejected... in which case apologies in advance
If a major issue is the cost per metre of the SDI cable itself, how
difficult would it be to either (1) remove the existing connectors on
drive and controller and creatively use a connector more suited to
cables currently available, or perhaps slightly easier (2) use the
existing connectors but fabricate a short "transition cable" with SDI
connectors one end, a short length of genuine SDI cable, and then a
more contemporary connector which can be used with a more contemporary
(cheaper) cable eg the already-mentioned RG62 to get to the other end
where there would be another "transition connector"? I realise that
every cable discontinuity (such as a connector) reduces signal
quality, but how sensitive to signal quality was/is SDI really?
Again, apologies if this makes no sense.
Lou
Not daft at all. The existing connectors on the drives and drive
controller are simple header connectors with two rows of pins on 0.1"
centers, similar to the Berg connectors we are used to seeing on
everything else from dec. The board mounted connector shrouds are
slightly larger though (than a normal Berg) to accomdate the bigger
cable end connectors. This is why I would like to try to make my own
with the miniature coax and the header connectors that use crimp pins.
So, I would say that the connectors on the drives are already suited
to be used with existing connectors (but just not with connectors we
are used to using with coax, like BNC, TNC, SMA etc.)
As for the SDI cable itself, I think the going prices on ebay are
reasonable. I considered something like your idea 2, buying a length
of cable of ebay to cut up into pieces. However, after reading the AMP
literature, it looks pretty hard to work with. I was thinking of
leaving the existing connector on one end, and reterminating the other
end with the previously mentioned header connector with crimp pins. It
might be even harder to go to a proper coax connector - this stuff is
really small!
Your question about the real sensitivity to signal quality of SDI
is a good one. The connectors used at the ends of the cables have got
to be pretty lossy. From ham radio experience, this does not look like
a low-loss way to terminate coax. This is why I think I have a
fighting chance at making homemade cables (and I only need them a few
feet long).
Lou