[QuadList] RCA Color Tape

[Don Norwood]

John:

The first quads (from both Ampex and RCA) had no timebase correction, and relied totally on the stability of the electromechanical components to reproduce the signal with minimal timing errors.  However, this approach does not have the stability required to reproduce the color information without considerable errors which must be corrected by removing the jitter from the chroma signal.  At that time, the heterodyne system was the only known way to accomplish that and it was used until the introduction of Amtec and Colortec allowed for direct recovery of color thru electronic time base correction.

That being said, RCA and Ampex used different methods for the early color playback.  RCA used bandpass filters to separate the luma and chroma from the composite playback signal, then used a heterodyne process to remove the phase errors from the chroma and recombine it with the luma to form the corrected color composite output.  Ampex used a different approach and decoded the composite signal into Y, I & Q, and then re-encoded the signal using station reference 3.58. 

Since in both systems the recording process was direct, a first generation LBC recording can be played back with fully phased color, but a second generation must be played back in the non-phased color mode.  However, I believe the original question may have had more to do with the other parameters of the early RCA system.  This obviously predated the low band color standard, and so different modulation frequencies, emphasis curves, etc. may have been used in the original machines.

Don


  ----- Original Message ----- 
  From: John Walko 
  To: 'Quad List' 
  Sent: Tuesday, November 10, 2009 10:37 AM
  Subject: Re: [QuadList] RCA Color Tape


  Chris:

  Forgive my ignorance, but why was it done this way?  I mean, wouldn't it have made sense to record at full bandwidth and then playback at full bandwidth rather than separating it from base band?

   

  Did this have something to do with bandwidth limitations with NTSC broadcast?

   

  It never fails to amaze me how complex a piece of machinery a Quad videotape machine is.  The guys who designed and built these machines were pretty intelligent.to say the least.

   

  Thanks;

   

  John Walko

  Media Archive Manager

  Scene Savers

  www.scenesavers.com

  800-978-3445

   

  From: quadlist-bounces at quadvideotapegroup.com [mailto:quadlist-bounces at quadvideotapegroup.com] On Behalf Of Chill315 at aol.com
  Sent: Tuesday, November 10, 2009 8:33 AM
  To: quadlist at quadvideotapegroup.com
  Subject: Re: [QuadList] RCA Color Tape

   

  RCA used direct color for the recording.  Nothing was done to the signal.  It was recorded at full bandwidth to the tape.

   

  The playback was where the interesting process took place.  The color was separated from the base band.  Then in a heterodyne process, the color was stabilized back to 3.58.  The jitter was removed and then the two were put back together.  The result was a viewable signal but the color was no longer locked to the video.  Thus it could not be mixed with another signal or much of anything else.  This process worked without the servo being locked to either vertical or horizontal.  That was a unique way to do it.

   

  As a side point, if you ever wondered what the "Non Standard" position on the Colortec was used for, it was used to play back a tape that was copied from a machine that used the RCA method to stabilize the color.

   

  Chris Hill



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