Re: [Discuss-gnuradio] USRP2 External Clock

[Matt Ettus]

Mamoru Yamamoto wrote:
> Would you please inform us what spec. 10MHz 
> and 1PPS signals are needed?  What waveform 
> are they?  

The Reference input can take a square or sine wave input, it is 
DC-blocked and is terminated in 50 ohms.  The input should be less than 
3V pk-pk.

The PPS input is not DC blocked.  It is AC terminated in 50 ohms, DC 
terminated in 1K.  The digital signal you put in should be between 0 and 
5 V.  It should never go below 0V and never above 6V.

> What phase relation do you expect 
> between 10MHz and 1PPS? 
>   

The PPS signal should be synchronous to the 10 MHz reference.

It doesn't actually have to be a PPS signal, it can be any digital 
signal, but you would need to figure out how to deal with it in the FPGA.

> It is helpful if you could show us examples 
> of the matching GPS clock/receiver models, too.
>   

Nearly any GPS frequency reference should work.  Everything from 
http://jackson-labs.com would suffice.  Tell them I sent you :)

> May I just miss finding the information 
> from the wiki?
>   

I will put it there.


Thanks,
Matt