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 <[email protected]> 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 <[email protected]> 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 <[email protected]> >> To: Discussion of precise time and frequency measurement >> <[email protected]> >> Subject: Re: [time-nuts] HP 3586A/B/C entirely referenced to 10MHz: >> Asolution >> Message-ID: <[email protected]> >> 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 >> >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
