[time-nuts] yet another GPSDO design, or so
ewkehren at aol.com
ewkehren at aol.com
Tue Jun 29 17:57:21 UTC 2010
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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