[time-nuts] TICC / TimeLab fun

[Bob kb8tq]

Hi

You have three inputs to the TICC:

1) The “frequency standard” input that delivers 10 MHz to the device.

2) The (likely pps) to channel A

3) the (likely also pps) to channel B

The device runs a continuous time count based on the frequency standard input. 
Each edge it sees on channel A gets a time stamp indicating when that positive edge
happened. It will keep on counting time for quite a while ( = I forget how long  :) ). Yes, 
this *assumes* you have the TICC set to time tag. If it is set to something else, you will get
whatever you asked for. 

If all you have is a pair of standards, put one into the 10 MHz and the other into channel A
or channel B. That gives you the whole picture of what’s happening with the two standards.
You have two devices and thus only one difference. It will show you that difference. 

Unless you have a third accurate standard, that’s as far as you can go. TimeLab needs to understand
what it is being fed. If it does, you will get a plot of some sort. It may be the noise floor of the
TICC.

With a third standard, it depends a bit on just *where* you decide to feed it in. Does it go into
the reference input at 10 MHz? Is it one of the “likely a pps” signals? In most (but not all) cases
it does go into the 10 MHz input. 

First step in doing three is to do a noise floor check. Grab a piece of coax to offset the pps to 
channel A vs channel B. With a single source feeding both inputs (and the device set up properly)
the data output (chan A vs chan B)  will be the noise floor of the TICC. If it’s not, either the TICC
has a setup gotcha or TimeLab does not understand what it needs to do.  To keep everything happy
coax in the range of 20 or 30 feet should work fine. 

The same process (sort of) could be done with a device that delivers both a pps and 10 MHz. You
could feed it into the TICC the same way as a two standard test. The result would be the noise floor
of the TICC plus the noise  in the 1 pps divider chain. Is the divider in this or that device more or less
noisy than the TICC? Who knows …...

Bob

> On Apr 29, 2020, at 1:12 PM, Chris Burford <cburford1 at austin.rr.com> wrote:
> 
> I'm trying to characterize a pair of GPSDO units using the TICC / TimeLab.
> The issue I'm having is when both GPSDO units are wired simultaneously to
> the TICC the resulting ADEV plot looks a little strange, beginning at
> 3.74E-1. Both GPSDO units are referenced against my PRS-10 Rb for the clock
> source.
> 
> If the GPSDO units are wired individually to chA then all seems fine and the
> plot begins with a more anticipated value of about 1.4E-8. I'm at a loss as
> to where to proceed from here to get both units characterized
> simultaneously.
> 
> Thanks for the assistance.
> 
> Chris
> 
> 
> <TICC Both Channels.png><TICC Single Channel.png>_______________________________________________
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