[time-nuts] questions on uncompensated crystal oscillators

[Magnus Danielson]

From: SAIDJACK at aol.com
Subject: Re: [time-nuts] questions on uncompensated crystal oscillators
Date: Wed, 5 Jul 2006 16:51:43 EDT
Message-ID: <578.15d8a.31dd805f at aol.com>

> Hi Magnus,

Hi Said,

> yup, that +-810Hz is the number I had in mind on the receiver side. The  
> tighter <3ppm numbers you mentioned are for the broadcaster side I  think.

Well, these are the requirements on the transmitted signals, made such that
the receivers will receive the signal properly. In particular is the maximum
drift rate of interest, the colour carrier may drift at maximum 100 mHz per
second. This is to avoid the shift in colour (which is encoded as the phase-
difference between the colour burst and the I/Q-modulated colour signal).

So... in the end, any equipment claiming compatible to PAL & NTSC needs to
comply to this standard. As we both know, real life is different.

> Although it sounds like a huge deviation from what we are  used to discuss 
> here (0.001ppb versus 30ppm) it presents a very challenging  engineering problem 
> since the factories don't want to pay more than about $0.25  for this 27MHz 
> oscillator.

Indeed.

> Most TV's can achieve lock with larger errors (I've seen up  to +-3KHz in 
> some cases) and interestingly enough, the better the TV, the  smalller the 
> lock-range. Sony professional Studio Monitors cut back on the range  to improve 
> picture quality, and won't do much more than the 810Hz...

There is no reason for them to support wider range than that, and if any
equipment doesn't comply, toss it. At least that's the only way we can act in
the professional side of things.

> Don't be demoralized, the fix is easy - feed a good 27MHz into your AV  
> equipment (preferrably from a GPS Disciplined frequency reference. You could use  
> our FireFox synthesizer for example - but that would be total overkill :)

I make sure that at any time I get the chance, I recommend my customers to have
their network clocked to some suitable UTC source. I also recommends that the
TV & radio production be suitably and similarly synchronised.

> Also, to reduce the problem to a skipped-frame/repeated-frame issue you can  
> use non NTSC/PAL baseband standards such as Component-out or HDMI out  etc.

Well, that's not my problem.

Cheers,
Magnus