Re: USRP2 External Clock


#1

Matt,

Note the “Ref Clock” connector on front panel:
http://gnuradio.org/trac/wiki/USRP2
It takes a 10 MHz reference.

I am very interested in this feature of USRP2.

Would you please inform us what spec. 10MHz
and 1PPS signals are needed? What waveform
are they? What phase relation do you expect
between 10MHz and 1PPS?

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

May I just miss finding the information
from the wiki?

Regards,


Mamoru Y.
Research Institute for Sustainable Humanosphere (RISH)
Kyoto University
removed_email_address@domain.invalid


#2

Mamoru Y. 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 :slight_smile:

May I just miss finding the information
from the wiki?

I will put it there.

Thanks,
Matt