[time-nuts] Fury Realhamradio listing

[Randy Warner]

TVB et al,

>From my experience with the M12+ and M12M, most of the diurnal shift is due
to shortcomings in the atmospheric models. If you plot the 1PPS on two
receivers sitting side by side you will see a definite shift over about an
hour or two during the time when the sun sets and rises.

When I was at Synergy we were trying to qualify a SigNav timing receiver
when it looked like the M12 series was going to disappear forever (even if
it stayed around SiRF had no interest in adding raw measurement messages).
The diurnal 1PPS shift was amazingly bad. Turned out the math in their code
was wrong. Once they corrected their code the SigNav's diurnal drift was
almost identical to the M12 series.

Secondary reason - As TVB said, temp can be an issue because the M12/M12+
receivers have crystal oscillators where the M12M has a TCXO. Naturally if
the temp in your lab goes up during the day and down at night you will see
some movement.  

For some REAL excitement, try blowing air over the crystal on the M12/M12+.
You can kill the receiver for quite a long time until the M12 re-sync's. The
M12M display a little of this behavior, but it naturally is quite a bit
better because of the TCXO.

Because of this, we always added a little piece of foam (weatherstripping
works great) over the crystal on the equipment we built for sale. It really
saves a lot of head-scratching when the receiver is mounted out in the open
(or worse, in front of a thermostatically controlled fan!)


Randy Warner
Senior Applications Engineer
Geodetics, Inc.

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Tom Van Baak
Sent: Monday, August 20, 2007 12:43 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Fury Realhamradio listing

); SAEximRunCond expanded to false
Errors-To: time-nuts-bounces+randy=geodetics.com at febo.com RETRY

> We do see differences in our Fury GPSDO when it is running using an  M12+ 
> versus an M12M (all else being the same), the M12M receivers seem to have

> significantly less diurnal pertrubations than the M12+ (well, we are
talking  

Said,

I could be wrong, but diurnal perturbations sound like antenna,
location, or placement more than receiver. 12h or 24h period?

When you get to this level, the details about antenna model
and antenna placement start to make a difference. I wonder,
for example, if the M12M has more inherent noise immunity,
which for your location, makes it look better than an M12+.
Or if there are tempco issues.

Hard to say. Anyone else done a raw comparison between
those two receivers? Or do they vary slightly, unit to unit,
more than they vary model to model?

/tvb


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