[time-nuts] LTE-Lite module

Charles Steinmetz csteinmetz at yandex.com
Sun Oct 19 07:48:43 EDT 2014


Bill wrote:

>How tough would it be to mate the 10Mhz version up to a really good 10811?
>*   *   *   I was thinking of throwing the LTE-Lite and the 10811 in a box.

Unfortunately, to get the best out of the local oscillator, the 
control PLL must be carefully adjusted so that the oscillator itself 
controls the stability at averaging times (tau) where it is better 
than the GPS (generally, up to tau of several hundred to maybe 
several thousand seconds), and the GPS controls the stability at 
longer tau.  The LTE-Lite has fixed (non-adjustable) loop parameters 
that cross over to the GPS at much lower tau than is appropriate for 
a good OCXO (but well suited to the installed TXCO).

The other day Said (I think) mentioned some hacks that may sort-of 
improve the ability of an LTE-Lite to discipline an OCXO, but that's 
all they are -- very approximate hacks.  There is really no way to 
properly mate an OCXO to the LTE-Lite control loop, which would 
require adjusting the PLL loop gain and the location of the loop's 
poles and zeroes (and possibly even adding new poles and 
zeroes).  That would need to be done by changing the PLL parameters 
internal to the LTE-Lite, which are inaccessible.  Without such 
reprogramming, the LTE-Light can never get the best out of an OCXO.

Best regards,

Charles





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