[time-nuts] Lady Heather numbers

Charles P. Steinmetz charles_steinmetz at lavabit.com
Sun Mar 3 00:52:23 EST 2013

Peter wrote:

>The antenna has a pretty clear sky view right now.  I have about 75 
>feet of cable, 25 feet that came attached permanently to the 
>antenna, might be RG-59, and a 50 foot extension which is a new 
>piece of good quality RG-6 CATV cable.
>Perhaps the antenna (came with the tbolt in the ebay deal) is not 
>that good and I should get something better before taking the effort 
>to get it up in its permanent location?

If you are not using a timing-grade antenna, changing it would be a 
good idea -- but be prepared for your c/n numbers not to change 
dramatically.  If you get a new one, make sure it is a 5 V antenna.

You say that the E and S exposures are pretty much clear, but the 
plot shows poor c/n below 30-45 degrees elevation.  You may find that 
your ADEV improves if you change the elevation filter to 30 degrees 
(it is at 10 degrees now), or change the signal strength filter to 
something >= 3.0 AMU (it is at 0.0 now; 3.5-4.0 is often 
recommended).  Either of these would reduce the number of satellites 
used by the Tbolt at any given time, but getting rid of the noisiest 
signals may improve overall performance as long as it does not cause 
the Tbolt to go into holdover for lack of satellites.

One of my Tbolts is in a location surrounded by tall trees and I have 
an indoor backup antenna in case the external antenna fails.  Using 
the backup antenna, its c/n plot looks not too different from 
yours.  After much experimentation, I found that the best performance 
with the backup antenna is achieved with the elevation filter set to 
30 degrees and the signal strength filter set to 3.0 AMU.

Best regards,


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