[time-nuts] Fury Realhamradio listing
SAIDJACK at aol.com
SAIDJACK at aol.com
Sun Apr 29 01:05:16 EDT 2007
In a message dated 4/28/2007 19:14:40 Pacific Daylight Time,
tvb at LeapSecond.com writes:
>In reporting 1PPS TI, did you measure what averaging
>time the Z3801A uses? And what averaging time do you
>use in your Z3801A emulation?
What I found in the Z3801 manual was that they use some sort of averaging on
their TI number (see page 3-20 for example). Does anyone know their
algorithm for this? There is no specification or details how their TI value is
calculated. So far no one seems to have inquiried about averaging done by the
Z3801A on the TI output values.
We do not emulate the Z3801A for comparative reasons, we implemented the HP
commands simply to get GPSCon running. Again we are following the 58503A more
closely than the Z3801A and are not trying to replace the Z3801A (That would
mean the user would have to buy a clunky old 48V power supply now, wouldn't
>I ask because the single-shot granularity of the Z3801A
>appears to be around 100 ps, at least the TI value of a
>Z3801A syst:stat is always a multiple of 0.1 ns. For a
>fair comparison, what is equivalent the Fury single-shot
They can get 0.1ns resolution on the printout because of averaging. I don't
know what their native granularity is.
Single shot resolution may not have such a significant impact since the GPS
used in the Z3801A is so much worse than the M12+.
Our resolution is more coarse than 100ps, but our inherent GPS noise is very
significantly lower than the Z3801. Resolution of 100ps with a peak to peak
noise of 100ns or more is not as good as peak to peak noise of 31ns with RMS
noise of <10ns.
So even if they have true 100ps hardware resolution (I somehow doubt it
since an expensive 54132A only has 150ps resolution) then that's more than two
orders of magnitude less than their sawtooth noise - does it really matter at
>Second question, I'm not sure "30 picoseconds" means
>anything. I mean, this is a GPSDO -- and so when you
>talk about its average value compared to UTC it seems
>you're just comparing the Fury with itself, right? What
>am I missing?
Well, this is the number that GPSCon gives. You may need to ask Graham what
the significance of this number is.
GPSCon calculates the average of all samples over the power-on time
intervall. Same way to measure it for the Z3801A and the Fury. Just comparing the
Z3801A plots with the Fury plot.
>From what I see online, the Fury is better for short (55hours+)
measurements, so overall less bias I would think. It's only been running a short time, so
we shall see if it can maintain this small average error long-term.
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