From: [EMAIL PROTECTED] Subject: Re: [time-nuts] questions on uncompensated crystal oscillators Date: Wed, 5 Jul 2006 16:51:43 EDT Message-ID: <[EMAIL PROTECTED]>
> 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 _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
