[QuadList] Fwd: FM standards in 525 and 625

[David Dean]

Hi All

 

I attach the relevant detail from the AVR2 theory of operation,.which nearly
agrees with you. Hope it helps.

 

Kind Regards 

 

David Dean

Westpoint Television

Now with Snell Shakeout

0208 742 3400

 

  _____  

From: QuadList [mailto:quadlist-bounces at quadvideotapegroup.com] On Behalf Of
chill315 at aol.com
Sent: 22 November 2013 17:13
To: Quad List; ted at flashscan8.us
Subject: [QuadList] Fwd: FM standards in 525 and 625

 



Chris Hill


Begin forwarded message:

From: Chill315 at aol.com
Date: November 21, 2013 at 9:36:32 PM EST
To: quadlist at quadvideotapegroup.com
Subject: FM standards in 525 and 625

I just hung up the phone with Ted Langfell, our illustrious secretary.  We
are having a discussion about the standards used for recording signals on a
quad.  This came about because a manual for an AVR-1 had a frequency for
blanking different than a VR-1200 manual.  He believes it was 5.3 vs 5.6
MHz.  He is driving so can not check the email.  

 

So here is the research that I did while on the phone.  I continued after we
hung up.  Both RCA and Ampex tell us that they conform to the SMPTE and EBU
standards. The referenced standards are SMPTE RP-6 for Modulation Levels.
The RP-10 standard describes the Signal Specifications.  The 625 system
conforms to CCIR Document DOC. X/27E-3 as set forth from the EBU.

 

525 Low band mono is from 4.28 for sync tip,  5.0 for Blanking, and 6.8 for
peak white.  Pre / post emphasis is 4 db at 4 MHz.

 

525 Low Band Color is from 5.5 for Sync, 5.79 for Blanking, and 6.5 for peak
white.  Pre / post emphasis is 9.54 db at 4 MHz.

 

625 low band is sync tip at 5.0, 5.54 for blanking, and peak white at 6.8
MHz.  Unknown emphasis curve.  

 

I did a math solution and came up with 5.54 MHz for the blanking.  This was
based upon a linear relationship based upon the .7 to .3 ratio of video and
sync as published by Ampex.  This is the specification that is in question.


 

But the top frequency is for PEAK WHITE.  does that mean over 100 units of
video?  If not, how much?  If 120 video plus sync, then blanking is lower in
frequency.  An interesting math problem.  And a good discussion.  Also the
modulators clamp at Blanking so in reality the deviation is kind of
controlled by the video level alone.

 

525 High band is 7.06 for sync. 7.9 for blanking, and 10.0 for peak white.

 

625 High Band is 7.16 for sync. 7.8 for blanking, and 9.3 for peak white.

 

Super High Band is 9.2 for sync and 12.2 for peak white.

 

All information is from VR-1200 and TR-4 manuals.  I also referred to
Ennes's book on VTR theory.

 

So what is the reason for the discrepancy?  A misprint?  The sales
literature does not list the frequencies.  Or was there a change by the EBU
or SMPTE in the standard after the design of the AVR-1?

 

As a side note, we know that there were different standards when both AMPEX
and RCA first introduced the machines.  That is why there was a special
setting on the TRT series demod's that allowed you to screwdriver adjust the
curve to get proper playback.  This also appears on the TR-22 and other low
band quads from RCA.  The standards were settled early on by the SMPTE as
the governing body.  Both RCA and AMPEX licensed each other so that the
machines would be compatible.  So if one developed a new standard, the other
had to adopt it for conformity.  We did not need the Beta vs VHS was in
broadcasting quads.

 

Chris Hill

 

 

 

 

 

 

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