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

paul swed paulswedb at gmail.com
Tue Mar 22 15:19:21 UTC 2011


ooops the chip is a 9833 and does have msb out same package 12 MW.
Thats what I am looking at for the 60 Khz rcvr.
But will use the 5932 because I have them to start with. Will use the 5932
MSB out to directly drive the LO of a tracor 599 rcvr. So much of that rcvr
can be simplified and perhaps improved with todays technology.
Regards

On Tue, Mar 22, 2011 at 9:07 AM, paul swed <paulswedb at gmail.com> wrote:

> It would take little to go to another DDS like the ad 9831 $8 at digikey.
> It does not have the msb though so Bert its back to bypassing the one
> resistor feeding the modulator.
> Changing the program for more bits in the tuning word would be quite easy.
> But the AD5932 is doing a great job so not sure when anything would
> actually change.
> Now if someone was going to build a project or kit that might be a
> different consideration.
> Regards
> Paul
> WB8TSL
>
>
> On Tue, Mar 22, 2011 at 7:48 AM, Bert, VE2ZAZ <ve2zaz at yahoo.ca> wrote:
>
>> Hi Bill,
>>
>> It is a great analysis you did. The truth is I found the AD5932 more or
>> less
>> randomly while searching for DDS chips. I computed the accuracy with a
>> 100KHz
>> MCLK and found that I would get better than 0.001 Hz. I knew that I would
>> never
>> be bang on, so I did not try to pinch more bits. This of course later
>> became 0.3
>> Hz as I increased to a 10MHz MCLK. But the unit was already on the bench,
>> installed on the A22. If I had to do it again, I would consider other DDS
>> chips,
>> as long as the price is similar.
>>
>> In the end, since I know what the offset is, I just take it into account
>> in my
>> frequency calculations. Even with a better DDS, I would have still taken
>> it into
>> account. Spectrum Lab can go quite far in its averaging calculations.
>> Besides,
>> my main objective was to stabilize the HP 3586 more than try to be exactly
>> on
>> frequency. So in that sense, I have met my objectives.
>>
>> I am glad to see that my SLM mod will be used as a starting basis for
>> future
>> improvements!
>>
>> Thanks for your input.
>>
>> Bert, VE2ZAZ
>>
>> ------------------------------
>>
>> Message: 6
>> Date: Mon, 21 Mar 2011 18:32:07 -0700
>> From: WB6BNQ <wb6bnq at cox.net>
>> To: Discussion of precise time and frequency measurement
>>    <time-nuts at febo.com>
>> Subject: Re: [time-nuts] HP 3586A/B/C entirely referenced to 10MHz:
>>    Asolution
>> Message-ID: <4D87FC17.892DE535 at cox.net>
>> Content-Type: text/plain; charset=iso-8859-1
>>
>> 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
>>
>>
>>
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