[GPS_Standard] Measuring Frequency difference (was: Ovenaire OSC 49-61C)

[Bert, VE2ZAZ]

Hi all,

To measure the frequency difference between my GPS standard and a known good
reference, I zero-beat the 2 signals by summing them through a resistive
splitter and I send the sum into a 10MHz radio receiver. I simply measure
the s-meter periodically using a digital voltmeter hooked up via GPIB and
controlled by Labview. I measure the time between 2 signal nulls and derive
the frequency offset. If anyone who does Labview is interested in my .vi,
let me know and I will send it through email.

Cheers,

Bert, VE2ZAZ

----- Original Message -----
From: "Geoff Blake" <geoff at palaemon.demon.co.uk>
To: "Zack Widup" <w9sz at prairienet.org>
Cc: <gps_standard at mailman.qth.net>
Sent: Monday, January 28, 2008 6:25 AM
Subject: Re: [GPS_Standard] Ovenaire OSC 49-61C


On Sun, 27 Jan 2008, Zack Widup wrote:

> On Sun, 27 Jan 2008, Geoff Blake wrote:
>
> > OK, so I had to go into work....
> >
> [snip]
> >
> > Does anybody have a link to a simple design that I can lash up to
> > simply compare phase between two 10MHz oscillators?
> >
> > 73
> >
> >
>
> I just hook them to the H and V inputs on a scope and look at the
> Lissajous figure. Extremely accurate.

Hi Zack, list,

Yes, the Lissajous figure is an easy way to do it, but when you
are comparing parts in 10^10 at 10MHz, you are looking at a
1000sec. cycle time or longer - boring!

The Rohde & Schwarz XSRM frequency standard incorporates a XSRM-Z3
phase comparitor which may be used to compare an unknown
"standard" with the XSRM itself. This produces a phase difference
output calibrated in nSec which may be fed to some form of
recording device.

Simplistically it is just a R/S flipflop set by the leading edge
of one sine wave and reset by the leading edge of the second sine
wave. The width of the Q output and via a LPF the mean voltage of
that output indicate the phase difference. To make one would not
be an insurmountable design task - even for me, but why should I
re-invent the wheel?

Any ideas folk?


73 de Geoff
--
    Geoff Blake G8GNZ      located  near  Chelmsford,  Essex,  U.K.
    Please reply to:      geoff(at)palaemon(dot)demon(dot)co(dot)uk
    Using Linux on  Intel & Linux  or NetBSD on Sun Sparc platforms

    Please  avoid  sending  me  Word  or  PowerPoint  attachments.
    See    <http://www.gnu.org/philosophy/no-word-attachments.html>
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