[time-nuts] FE-5680A Mechanical Question

shalimr9 at gmail.com shalimr9 at gmail.com
Sat Jan 14 14:13:52 EST 2012


Here is a common misconception. Most consumer grade "24bit" sound cards only have 16 bit ADCs but 24 bit equivalent DACs (most of them are actually 1bit DAC with oversampling.)

You have to spend a pretty penny to get a 24 bit ADC running at multiples of 44ks/s.

Further, the very poor DC performance of the typically sound card 16 bit ADC is hidden by the analog and digital filtering of the card and the driver.

If anyone has an inexpensive (<$100) sound card with true 24 bit ADC (if they are capable of DC, so much the better), please let me know because I have been looking for one.

Didier KO4BB

PS: to remain on topic, I agree with the principle of using a PC to breadboard something, as long as the hardware interface remains simpler than a cheap microcontroller, bit it is easy to get carried away and build PC-based hardware for the purpose of running a test, and having to redo all from scratch to convert it to a uC solution for the final application.


Sent from my BlackBerry Wireless thingy while I do other things...

-----Original Message-----
From: Chris Albertson <albertson.chris at gmail.com>
Sender: time-nuts-bounces at febo.com
Date: Fri, 13 Jan 2012 08:15:42 
To: Discussion of precise time and frequency measurement<time-nuts at febo.com>
Reply-To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: Re: [time-nuts] FE-5680A Mechanical Question

On Fri, Jan 13, 2012 at 3:19 AM,  <EWKehren at aol.com> wrote:
> What we know is that you can set the Rb in 7 E-13. Dithering would allow
> even closer setting, the question is what rate will the Rb accept with out
> loosing lock or deterioration of the performance. Some one should explore
> that.  I am still waiting to se some aging. Taking the 10 MHz output and than
> use an  analog loop and something like a Morion OCXO and you have the best of
> all.
> Digitally controlling the Rb will cut the cost of the control loop in half.
>  For $10 in parts and a PC board for less than $10 using Shera like
> controller  can be realized. What is needed is some one able to do the PIC.
> If some one is interested and able, please contact me off list. A low cost
> GPS or a 1 pps output of a Tbolt be perfect source.
> Bert Kehren

Don't use a PIC for the prototype.  A desktop PC could work as well
and everyone here already has one.   Connect the FE5680 to the PC's
serial port and send commands to adjust it.  The PC also needs to be
able to read a voltage.   Many already have audio input with 24-bit
ADC chips.

Later you can move the C code from the PC pretty much directly to an
AVR.  PICs typically use assembly language, that is harder and limits
the number of people who can contribute changes to the code.  But you
can start with a PC, maybe running Linux or BSD.
Chris Albertson
Redondo Beach, California

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