On 10/17/15 6:17 AM, Alex Pummer wrote:
actually, that is a ketch 22, if the loop bandwidth is to low, you will have low noise , but it may will not lock at all, an other way to try to filter out the noise, also you may make the loop filter digital, but leave the the PLL analog, that could have the possibility to have the advantage to be able to change the loop bandwidth increase for locking, and reduce after the detected locking
changing loop bandwidth between acquisition and tracking, or, similarly, (effective) loop bandwidth that changes with SNR are pretty common strategies.
In the deep space transponder world (where you are acquiring and tracking a very narrow carrier at -155 or -160 dBm against noise of -170dBm/Hz) you also want to know what order filter you should be using in the tracking loop. If there's an expectation that the frequency being tracked is changing (e.g. Doppler), then a low order loop may not be the best choice.
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