[time-nuts] FE-.5680A trimming resolution (& TBolt)

WarrenS warrensjmail-one at yahoo.com
Mon Jan 30 16:14:10 EST 2012


Chris asked:
>LH reports the signal at 40dB, +-2dB.  Is that good enough?

Good enough for what? The TBolt can be setup to work with that, but it could 
certainly be much better.
With a good Tbolt antenna setup you should see about 50 db for overhead 
birds and in the high 40's for the lower ones.
With an indoor puck antenna I see mostly in the low 40's, and it still works 
OK, IF the Tbolt is set up for the lower signal level.
More important is the Antenna signal strength variations plotted over the 
whole sky which LH can do.
Look for low signal areas due to obstructions in the "SAS" plot and small 
delta "signal strength blips" in the "SAD" plot due to multipath 
cancellations.

ws

*************

----- Original Message ----- 
From: "Chris Albertson" <albertson.chris at gmail.com>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Monday, January 30, 2012 11:52 AM
Subject: Re: [time-nuts] FE-.5680A trimming resolution


On Mon, Jan 30, 2012 at 10:43 AM, Mark Sims <holrum at hotmail.com> wrote:
>
> These are 4-BYTE single precision floating point numbers, not 4 bit 
> integers. They are the values plotted in the Lady Heather PPS and OSC 
> graphs....

Sorry I type faster than I think.  You are right they can't be four bits.
I work in rocket telemetry,  you'd think I'd get this straight. I
write software to unpack this kind of stuff.


>  A much better approach is to minimize the system errors with a GOOD 
> antenna, accurate position survey, proper oscillator control parameters, 
> and temperature stabilization (of both the receiver and power supply)... 
> Lady Heather is willing to oblige on the last points. A good Tbolt 
> implementation can get the PPS plot to under a few nanoseconds of error.

I've done this.  I see values in the single digit nanoseconds.  I have
a timing antana on a mast on the roof.  Perhaps I could get a better
timing antenna and low loss coax lead.  LH reports the signal at 40dB,
+-2dB.  Is that good enough?

I've seen adev plots from an Oncore MT12
(www.leapsecond.com/pages/m12-adev/)  where these error estimates are
added in or not and they get maybe 20%  better with the corrects
applied.    the MT12 produces error estimates about that same size as
a T-bolt.

The data looks noisy on LH's graph because of the scale of the graph.
Compared to the 1PPS it is a smooth function.

Chris Albertson
Redondo Beach, California







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