[time-nuts] Fury Realhamradio listing

Magnus Danielson cfmd at bredband.net
Sun Apr 29 07:12:03 EDT 2007


From: Dr Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Subject: Re: [time-nuts] Fury Realhamradio listing
Date: Sun, 29 Apr 2007 17:20:03 +1200
Message-ID: <46342B03.4020302 at xtra.co.nz>

> SAIDJACK at aol.com wrote:
> > 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 
> > that point?
> >   
> Said
> 
> Obtaining 100ps resolution, particularly when one is only making 1 
> measurement per second, is relatively easy and inexpensive to do with a 
> few discrete components.

Indeed. Three-four transistors and a handfull of caps and resistors. The
Z3801A uses the 10 MHz clock and thus require a x1000 interpolation, which is
easy enought to acheive. Look at the HP5335A service manual for further
details. What you do is that you stretch the error-pulse (1-2 cycles) by
charging a cap with one current and discharging it with another, the output is
then run into a comparator for the sake of gain. This stretched pulse is then
measured with the coarse clock and voila!

Cheers,
Magnus




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