From: ins_wayne@actew.oz.au
Newsgroups: rec.video
Subject: A: How to make a long S-Video cable
Date: 10 Jan 93 00:06:23 EST
Organization: ACT Electricity & Water

  Well, folks...

  I've built a prototype 20m cable.  It's not pretty, but it works
  fine.  Initial impressions: worthwhile, but only just.  I'll
  have to look at a broadcast test pattern to be sure.  An S-VHS
  recording of a Test Pattern showed little improvement, but S-VHS
  recordings of normal program material is quite a bit sharper. 

  No noticeable degradation in Chroma or Luminance information. 
  Black-level noise is minimal to non-existent.  Cross-talk and
  moire effects are reduced, as expected.  Sharpness is better.

  (My gear seems to work very well on plain old composite; there
  is a noticable improvement, but it's only in the 5-15% range.  My
  projector is now being driven to near limit of its resolution.)

  I started with 20m, as this was the longest I'd ever need; if
  necessary, I was prepared to chop 5-7m off and try again.  It
  wasn't necessary.  There is no perceptible difference between
  the 1.2m cable from VCR to projector and the 20m cable.

  I have overcome the problem of getting two large cables into one
  very small connector.  It's childishly simple!  My solution was
  to strip back the coax and insulate it with heat-shrink tubing.

  If you can find it, get a cable with two 75 Ohm coaxes inside an
  overall shield.  This is what the commercial ones apparently
  use.  It'll make assembly much easier.

  You will need;
      .	2x 4-pin mini-DIN plug (see TV repair shop)
      .	2x Run of RG59U Coax, to desired length (ie, 75 Ohm)
  	   (You need two runs, one for Y, one for C, same length.)
      .    2mm Heat-shrink tubing (in various colours if desired)
      .    Small vice or pliers with elastic band.
      .    Sharp Knife or Coax stripper.
      .	   Low-power Soldering iron & solder
      .    Electrician's tape for insulation & binding.
      .    Steady hands! (Preferably three or more.)
      .    A spare hour or so.

  I'd recommend getting a spare connector, just in case.  They are
  VERY fragile little things.

  If you look into the connector from the PLUG side, with the cable
  running away from you, you will see:


  	    Pin 1    Y     O   O    C   Pin 2

  	  Pin 3	 Ygnd    O       O    Cgnd  Pin 4.

  			    XXX  (key)


  In practice, it doesn't matter about left-right errors, because
  the cable has vertical symmetry.  Just be consistent.  The pins
  are arranged in a rhombus; the closer pins at top are signal, the
  ones further apart, near the key, are the grounds.  The grounds
  are usually connected at the device end, but don't count on it.



  What I did was:

  	Pop open the mini-DIN connectors
  	Strip back about 8cm of coax
  	Twist braid into a multi-strand wire
  	Remove all but 1cm of core insulator
  	Thread heat-shrink tubing onto each "wire" leaving about 2mm
  	Tin the pins (the CABLE side!) and wires 
  	Thread wires through connector shell
  	Solder wires to pins, placing wires on the "outside"
  relative to the other pins, thus minimising the probability of shorts.
  CORE goes to pin 1/2; BRAID goes to 3/4 respectively.

  	Repeat for Chroma, then repeat for other end.

  	Both ends look exactly the same.  Pin 1 is always in the
  same position, etc.

  	With a multimeter or continuity tester, verify
  that there are no shorts.  All pins should ONLY connect to their
  counterparts.  Correct any faults.

  	Shrink the heatshrink tubing over the pin and wire.
  	Reassemble connector housing & reinforce if necessary.

  	Final test for shorts.

  	Switch off equipment  (HIGHLY recommended)
  	Plug in cable
  	(Optional: Pray to favourite deity :-) )
  	Turn on for smoke test; be ready to unplug quickly. :-)
  	Check signal integrity; You should have a clean picture.
  	
  When all tested, you should tape the two coax runs together at
  regular intervals and run the cable in its final location. 
  Protect those ends!

  Conclusion: It's possible.  It works.  It seems worthwhile.
  It's MUCH cheaper than buying a ready-made one, IF you can get one.
  20 metres (about 60ft) seems well within the length limit if you
  use good cable.  Best to make it longer than required, as it's
  rather hard to glue extra bits of cable in. 

  Thanks to all who responded.

  Now for the fun bit!

-- 
Wayne Myles             Email: ins_wayne@actew.oz.au, wsm@ccadfa.cc.adfa.oz.au
System Manager,	        Snail: GPO Box 366, Canberra ACT 2601, Australia.
ACT Electricity & Water	   Ph: +61-6-248-3143 (w)  Fax: +61-6-248-3439
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