[time-nuts] time-nuts Digest, Vol 64, Issue 14

Mark Amos mark at amos-family.com
Sun Nov 8 17:57:39 UTC 2009


Bill, et al.

It's Sunday in Ohio and, as I ate my toast with the rising sun, humming
along with Sibelius, I did a few more tests using your Z axis suggestion -
Thanks!

I tapped Channel 1 (the Trimble GPSDO) and routed its signal to the Z input.
I made a recording of the pattern (two complete rotations, 720 degrees of
shift.) It is stored here: <http://members.toast.net/mark.amos/Trimble Z
axis.mov> 

I also tried tapping Channel 2 for the Z input (again, recording two
complete rotations:) <http://members.toast.net/mark.amos.LPRO Z axis.mov>
(These are huge files.)

Using dual-trace mode on the scope, the "direction" of the LPRO sinusoid is
clear compared to the stationary Trimble sinusoid (not recorded.)

The when I ran these tests yesterday (measuring 182 seconds for 360 degress)
it was with a homebrew GPSDO.  However, subsequent runs showed poor
irreproducibility of the results indicating that the homebrew unit might not
a very stable source - so I switched to the Trimble for succeeding
measurements, which have been very consistent.  I may not have noticed the
homebrew GPSDO problem if I hadn't compared it to the LPRO in these tests.

Obviously, for most of you, this is pretty basic stuff, but these "visual
aids" are useful for me to get an intuitive feel for the underlying
phenomena.

It will be interesting to watch the changes over time.  

Mark

----------------------------------------------------------------------

Message: 1
Date: Sat, 7 Nov 2009 18:08:59 -0600
From: "Bill Hawkins" <bill at iaxs.net>
Subject: Re: [time-nuts] Calculating frequency differences using
	Lissajoufigures
To: "'Discussion of precise time and frequency measurement'"
	<time-nuts at febo.com>
Message-ID: <0AB667ACA96F44819A8255AF686C3187 at cyrus>
Content-Type: text/plain;	charset="us-ascii"

Well, it's 5 PM in Minneapolis, so I joined my wife on the deck to toast
the vanishing sun. Didn't sing any Jimmy Buffet songs, though.

But, to the matter at hand. If your Lissajous pattern scope has a Z input
for intensity modulation, drive it with one of the 10 MHz sources. The
direction of rotation will be obvious, as the intensified portion chases
its way around the pattern.

Then again, maybe you need to phase shift one of the signals 90 degrees,
apply the straight and shifted versions of the same signal to X and Y so
you get a circle, and then apply the other signal to the Z input. That
would not be a Lissajous figure, though.

You would still need to observe any changes, unless you are certain that
the frequency difference will maintain the same sign. I guess that's what
drives people to buy GPIB interface cards and spend hours making the whole
thing work correctly.

Bill Hawkins




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