[time-nuts] HP 3586A/B/C entirely referenced to 10MHz: Asolution

paul swed paulswedb at gmail.com
Tue Mar 22 03:16:07 UTC 2011


Using spectrum lab I can not detect a stability issue but its not really
working at sub hertz resolution and not sure it really can.
There are many DDS chips out there at various price ranges and difficulties.
The AD5329 proves that the HP 3586 can be converted successfully and at sub
$10 cost. Thanks Bert.
Other issues to deal with 48 pin tsop packages etc. I had enough trouble
with 10 pins on the AD5329 so serial interface is desirable.
I am looking at the 9831 for a different use at $8. Must say technology is
great.
Regards
Paul.

On Mon, Mar 21, 2011 at 9:32 PM, WB6BNQ <wb6bnq at cox.net> wrote:

> Bert,
>
> I am curious to know what caused you and Paul to select the AD5932 device ?
>
> Admittedly, I haven't verified the Analog Devices simulator with real
> components,
> but I suspect their simulator is spot on or damn close.  Using the Adsim
> page I
> looked at a few different DDS’s to see what could be done.  With little
> additional
> cost better choices are available allowing better on-frequency accuracy
> relative to
> the offset values of the AD5932.
>
> The problem with AD5932 is the frequency tuning word [FTW] is too small.
>  So,
> clearly, increasing the FTW would give an immediate improvement as to
> accuracy.  A
> simple low pass filter would clean up the spurs as they are all associated
> with the
> clock frequency and well removed from the fundamental signal.  Some DDS
> selections
> included an uncommitted internal comparator stage (notably the 9834 and the
> 9851)
> that would serve well for squaring the signal after filtering.
>
> I ran simulations for two different DDS devices.  I picked ones that
> operated off of
> 5 volts of which there is damn few good ones.  The first one is the AD9834
> with a 28
> bit tuning word with a 10 MHz clock.  Here are the results:
>
> 13775 = 13775.0059366226 Hz = error of +0.0059366226
> 14125 = 14124.9969601631 Hz = error of -0.0030398369
> 14275 = 14275.0144004822 Hz = error of +0.0144004822
> 16425 = 1642500.01311302 Hz = error of -0.0088095665
> 16625 = 1662500.01639128 Hz = error of +0.0020265579
> 16975 = 1697500.01281500 Hz = error of -0.0069499016
> 17125 = 1712500.00596046 Hz = error of +0.0104904175
> 17475 = 1747500.00238419 Hz = error of +0.0015139580
>
> As you can see, with the additional 4 bit tuning word, the error improves
> for all
> except 17125 where it is equal.  The second run was upping the frequency by
> 100
> times to reduce the size of the filter components.  For the AD9834, this
> did not
> turn out well at all.  The wave form had a hard staircase appearance due to
> the low
> clock rate relationship (5:1) to the higher output frequency.  The same
> problem
> exists for the AD9851.  So, I scrapped that whole idea.
>
> The second run was using the AD9851 with a 32 bit tuning word with a 10 MHz
> clock.
> Here are the results:
>
> 13775 = 13774.9989517033 Hz = error of -0.0010482967
> 14125 = 14124.9992884696 Hz = error of -0.0007115304
> 14275 = 14275.0004306436 Hz = error of +0.0004306436
> 16425 = 16425.0005036592 Hz = error of +0.0005036592
> 16625 = 16624.9996982515 Hz = error of -0.0003017485
> 16975 = 16975.0000350177 Hz = error of +0.0000350177
> 17125 = 17124.9988488853 Hz = error of -0.0011511147
> 17475 = 17474.9991856515 Hz = error of -0.0008143485
>
> As you can plainly see, increasing the tuning word by, yet, another 4 bits
> allowed
> for shifting the error further to the right.  Maybe enough to put it beyond
> the
> resolution of the total measurement system and thus, perhaps, removing it
> from the
> systemic error list (i.e., less to worry about in the calculation).
>
> Unfortunately, Analog Devices has stopped producing some of their easier to
> use 48
> bit DDS devices.  The current run of 48 bit DDS’s are way more complicated
> and
> specialized, have issues with the clocking methods (time nut unfriendly),
> besides
> using lower voltages, they are harder for the hobbyist to mount to a board
> and they
> are more expensive.  Truly a sad circumstance for the occasional hobbyist.
>
> Bill....WB6BNQ
>
>
>
>
> "Bert, VE2ZAZ" wrote:
>
> > Hello Everyone,
> >
> > I have spent the last few weeks modifying the HP 3586 Selective Level
> Meter. The
> > intent was to modify the unit and reference the SSB product detector
> stage to
> > the internal reference. This would make the entire SLM locked to the
> 10MHz
> > reference, whether internal or externally fed.
> >
> > I have completed the modification with satisfactory results. I use a
> DDS-Based
> > Function Generator 16-pin IC and a small 8-pin PIC micro.  For more
> detail,
> > visit my website at http://ve2zaz.net/HP3586_AD5962/HP3586_AD5962.htm .
> >
> > This has been a very good exercise from a DDS perspective and I have
> learned a
> > lot on the topic. I would be interested in hearing from those who proceed
> with
> > the mod.
> >
> > Thanks,
> >
> > Bert, VE2ZAZ
> >
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