[time-nuts] Accuracy results with Trimble Thunderbolt?

[Frank O'Donnell]

I hope you all don't mind a novice-level question, but I'd be interested 
in any feedback on what I'm seeing with the accuracy of the 10 MHz 
signal out on my Trimble Thunderbolt.

I bought the Thunderbolt last year used on eBay, and it appears to be of 
about 2001 vintage. Most recently it's been running continuously for 
about 2 1/2 months, attached to a roof-mounted Lucent PCTEL 26db twist 
antenna with a clear view of the sky, with the receiver located in a 
room with a relatively stable temperature. Lady Heather and Thunderbolt 
Monitor both appear to report it to be well settled-in. My main use of 
the Thunderbolt is to supply a 10 MHz reference signal to an HP3586B and 
HP3336B for frequency measurement purposes.

At the beginning of this month I remember typically seeing about 20 ppt 
accuracy for the 10 MHz reference as reported in Heather. I then used 
Heather commands to initiate an autoset of oscillator parameters (set 
antenna elevation mask angle to 0 with FE keyboard command and set 
signal level mask to 1 with FL command in order to allow collection of 
signal level data across full sky; clear signal level history with CM 
keyboard command; let run at least 6-12 hours to build up new satellite 
signal level map; issue “&a” autotune command, allow time to complete). 
Now I seem to be seeing about 60 ppt accuracy on average.

For my purposes, these differences are probably academic -- if I'm doing 
my math right, 60 ppt in a 10 MHz signal is 0.0006 Hz, far down in the 
noise of frequency variation due to Doppler etc. Still, I guess I've 
drunk enough of the Koolaid to wonder about the accuracy level and any 
ways to improve it.

So, some questions. Is it possible that the increase in the error seen 
could be due to the oscillator parameter autoset sequence that I ran? If 
so, is there a way to remedy this? What would be typical accuracy for 
the 10 MHz reference on a Thunderbolt? Is there anything else I can do 
with the Thunderbolt itself to increase the accuracy?

If I want to consider an alternative to the Thunderbolt that might offer 
better accuracy, is there a logical next step?

Thanks for any suggestions,

Frank