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發表於 2015-4-15 00:15:08
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dCS reply:
GPS receivers and atomic clocks usually have an AC-coupled 10MHz output, with perhaps 1V rms amplitude. This means that the output signal will swing between about -1.4V and +1.4V each cycle, but this will vary between receivers and will be influenced by cable reflections. The ideal setting for the Coupling menu page when presented with this sort of signal is definitely AC, as the Reference Input stage will detect the change as the signal crosses zero volts. The Paganini Clock manual states that you should use the AC setting when using this type of source.
When set to TTL, the Reference Input is biased to detect signals as they cross the +1.3V level – this is intended for use with a Word Clock signal, which typically swings between +0.2V and +3V. This would probably not be detected at all on the AC setting.
If the output level of your GPS receiver is perhaps 0.9V rms, it will not quite reach the +1.3V switching point and will not be detected by the Clock’s input stage. This would explain why your Paganini Clock does not detect the signal on the TTL setting.
If your friend has exactly the same model of GPS receiver but it has a slightly higher AC coupled output level, it will be detected on either setting. However, using the TTL setting with an AC coupled signal is not the correct way to use the Clock and will result in increased jitter.
So, please set your Paganini Clock to the AC setting and advise your friend to do the same. |
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發表於 2015-4-14 21:44:13
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