[time-nuts] Newby with questions

[Bob Camp]

Hi

For a 1 ppm error, there are a lot of ways to get the job done. If you need
to be able to trace that error back to NIST or something like that, be
careful of how you set things up. 

For a "I just need it right" type of thing, either a TBolt or a free running
rubidium will give you what you need. If Lady Heather is showing the TBolt
running right, it's safe to assume it's within 1 ppm. 

To use the TBolt, you do need to be sure it's got good enough sky view to
always be locked. It will go into holdover if it does not have a good view.
>From your description you have a good view and the device is staying locked
to GPS. 

How to do a simple check on the TBolt?

The EFC sensitivity is about 3 Hz / volt. You can use LH to calibrate it to
a fairly good level. Hook a DVM up to the EFC (or watch the plot). If it's
moving less than 1/3 of a volt over a few hours, and it shows locked the
whole time - safe to say you are under 0.1 ppm and your 1.0 ppm cal is ok. A
reasonable TBolt that's powered up continuously should be way below these
levels (like by > 100X). 

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of David VanHorn
Sent: Monday, February 28, 2011 11:38 AM
To: time-nuts at febo.com
Subject: [time-nuts] Newby with questions

I have a thunderbolt up and running since last week Friday.

I'm doing this for a calibration source at work, eventually we will have two
antennas, feedlines, and thunderbolts, so that we can have one fail and keep
operating, but for the moment I just have the one receiver.  Both antennas
are mounted underneath a large skylight, as high as we can get them.  I
realize it's a compromise, but getting signals out to the roof will be a
problem so I'm trying to work it without taking the feedlines through the
roof if possible.

I've done the 48 hour survey, but my signal plot shows a big circular shaped
mouse bite on the north side. I'm showing no signal up through 70 degrees at
north, 30 degrees from NE around to NW.   How badly will this impact me?

Temperature:  My thunderbolt always reports -55C which can't possibly be
right.  :)   Is this some configuration in Lady Heather, or is something
broken?

Otherwise, things are looking pretty good, I'm showing an average error of
about 70ppt.

I'm working my way through learning Lady Heather, there's a lot displayed
there that I'm a bit fuzzy on, but in the end my main concern is that my 10
MHz output is as accurate as possible in the short term.  Our calibration
cycle will take about 4 seconds to run, and I need <=1PPM error on the
calibrated device.



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