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

EWKehren at aol.com EWKehren at aol.com
Tue Jun 29 18:07:17 UTC 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.
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

-----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

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 

n a message  dated 6/29/2010 12:21:31 P.M. Eastern Daylight Time,  
ists at rtty.us  writes:
Summing a pair of DAC's and checking them with an ADC  is  one way to get 
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  
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  
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
-----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:

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  
> 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
> find  and now  expensive and  the single step of the D/A is intended for a
>  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.

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