[time-nuts] GPSDO Question

[Bruce Griffiths]

GandalfG8 at aol.com wrote:
>
>  
> The Idaho State University version is reported on their web page for  the 
> project as having been checked over a 13 day period, by the Idaho National 
> Laboratories Calibration  Lab, and found to be accurate to 1.2x10^-10.
>  
>  
> regards
>  
> Nigel
> GM8PZR
>   
Nigel

The Idaho state project
http://www.geocities.com/isurflab/Frequency_STD_Project.html

Has the usual hallmarks of inexperience, fine for student educational
purposes but shouldn't be slavishly copied without understanding.
As usual the measurement technique and conditions used for the frequency
comparison are poorly documented.

Using an OPA2705 opamp as a comparator to produce a 5V logic level
output from the GPS receivers PPS pulse is probably an effective way of
adding jitter to this signal.
Even using an RS485 line receiver as used on the original VE2ZAZ
<http://www3.sympatico.ca/b.zauhar/GPS_Std/GPS_Std.htm> board is
probably a better choice despite its built in input attenuator. Even a
saturated switching transistor probably has better performance than the
opamp. Add a simple baker clamp to the transistor and the performance is
probably hard to beat for the outlay. Alternatively a 74HCT14 or 74ACT14
would also work well as a 3V to 5V level translator.

Using a switchmode power supply from a PC isnt exactly conducive to low
noise.

Bruce