[time-nuts] yet another GPSDO design, or so

EWKehren at aol.com EWKehren at aol.com
Tue Jun 29 14:07:17 EDT 2010


Hi again
This seller has 95  AD1861 in stock. Is there a reason why they would  not 
work for all applications. No I do not get a cut. 95 would justify to do a  
new design but I am convinced there will be plenty more.
Bert
 
 
In a message dated 6/29/2010 1:57:54 P.M. Eastern Daylight Time,  
ewkehren at aol.com writes:


Hi  again.
Any one interested should hold off for a day buying. I have  contacted the 
seller asked how many he has and what a quantity price would be.  To much 
interest and the price will go up. I think the market for audio  equipment 
replacement is shrinking and there will be more reasonable offers  out there 
for this device, because repair of the audio equipment is  prohibitive
Bert






-----Original  Message-----
From: EWKehren at aol.com
To: time-nuts at febo.com
Sent: Tue,  Jun 29, 2010 1:45 pm
Subject: Re: [time-nuts] yet another GPSDO design, or  so


Hi
just bought four AD 1861 on ebay with shipping was $11  each. Will see  
hat I get, but they are out there and 18 bit will  cover in my opinion most 
 
pplications
ert


n a message  dated 6/29/2010 12:21:31 P.M. Eastern Daylight Time,  
ists at rtty.us  writes:
Hi
Summing a pair of DAC's and checking them with an ADC  is  one way to get 
the
ob done. It's been used quite a bit. 
16  bit  DAC's are sub $3 items these days with pretty good specs on  the
arts. A  multi channel <1 ppm accurate 24 bit "DC" ADC is a  fairly common
art as  well. Raw parts cost from Digikey for PIC and  the rest of it  
except
eference) likely would be sub $20. If you  have all the parts  already I
uppose it could be free. Even with a $50  charge for a quick turn  PCB
here's not a lot being spent for the ADC  side of things. 
You  can spend a *lot* on a reference. That's going  to be true for any long
erm  stable stand alone EFC drive setup. My  guess is that reference noise  
n
ffordable parts may drive you to  the big R/C's. Putting at least  one
hannel of the ADC after the big  R/C lets you get a handle on  leakage
ssues. 
Bob
-----Original  Message-----
rom:  time-nuts-bounces at febo.com  [mailto:time-nuts-bounces at febo.com] On
ehalf Of  Bruce  Griffiths
ent: Tuesday, June 29, 2010 5:32 AM
o: Discussion of   precise time and frequency measurement
ubject: Re: [time-nuts] yet  another  GPSDO design, or so
Attila Kinali  wrote:
Moin,

On Sat, 26 Jun 2010 21:14:02  EDT
EWKehren at aol.com  wrote:


> What you  want is basically a  Shera Board. That design has been around  
or
> quite some time and  has served me very  well.
>      
Yes. The  Shera Board and similar  designs serve as an example for  me.


> I have  a total of six  running
> including two controlling Rubidium. There  are in my  opinion a couple of
> problems: not every 4066 works on  the design  the 18 bit D/A is very hard
o
> find  and now  expensive and  the single step of the D/A is intended for a
.7
>  E-13   frequency step.
>      
Yes. My goal  is to  update the venerable 4066 with something more
modern and  have  components that are easy to get trough farnell, digikey,
mouser,  and  all the other distributors. Yes, 16bit D/A seems to
be the  maximum  that is currently available. It crossed my mind
to build a  24bit R-2R  D/A using discrete components, but this might
have  actually a worse  performance than a off the shelf 16bit  D/A.
(temperature drifft,  resistor values missmatch, EMI,  etc)


Attila Kinali

ts  possible  to build a 24 bit resolution D/A using a synchronously  
iltered PWM  circuit.
pair of PWM outputs and a few relatively low  precision resistors  and 
apacitors together with a low noise low  drift reference are  required.
he technique takes advantage of the  fact that the required EFC  voltage 
hanges slowly and isnt updated at  a highg rate.
he  synchronous filter technique eliminates the very  long time constant 
C  filters required with an asynchronously  filtered PWM   waveform.
Bruce

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