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Re: [Discuss-gnuradio] USRP1 DBSRX 10MHz reference clock
From: |
Eric Blossom |
Subject: |
Re: [Discuss-gnuradio] USRP1 DBSRX 10MHz reference clock |
Date: |
Tue, 16 Jun 2009 11:41:52 -0700 |
User-agent: |
Mutt/1.5.18 (2008-05-17) |
On Tue, Jun 16, 2009 at 11:24:31AM -0700, Kutik wrote:
>
> Eric Blossom wrote:
> >
> > On Tue, Jun 16, 2009 at 08:23:37AM -0700, Kutik wrote:
> >>
> >> I would like to change the USRP master clock to 10MHz.
> >>
> >> I call urx->set_fpga_master_clock_freq(10e6) prior to
> >> usrp_standard_rx::make.
> >>
> >> I wonder how to set the REFCLK_DIVISOR in db_dbs_rx::_refclk_divisor().
> >>
> >> From all examples I have seen the (master_clock/REFCLK_DIVISOR) is 4MHz.
> >> This would mean REFCLK_DIVISOR must be 2.5, but on the other hand it must
> >> be
> >> an integer..
> >>
> >> Can I set the REFCLK_DIVISOR to 3 (resulting in Max2118 clock 3.33MHz)?
> >> Or
> >> would you recommend something else?
> >
> > Can you tell us what you are really trying to do? Why do you want to
> > change the master clock to 10MHz? The USRP won't function with that
> > slow of a clock. It won't be able to talk over the GPIF port to the
> > FX2 USB controller.
> >
> > Eric
> >
>
>
> Thanks for the answer,
>
> I would like to acquire narrowband data (200 kHz). In this range I'll
> receive multiple CW signals. The maximal frequency inaccuracy is 2kHz.
> Therefore USRP1 has to be disciplined by precise reference clock.
>
> I have 10MHz reference signal available, and hoped there will be no need to
> buy 64MHz oscillator (disciplined by 10MHz).
>
> I've read (usrp_basic.h) the master clock range is 10-64MHz, thus I wanted
> to give it a try.
OK, thanks.
After some off-list discussion, I think you should be able to make
this work. I expect that Johnathan or Matt will chime in with some
additional information. (The GPIF bus uses a clock from the FX2, so I
was mistaken about that being a problem.)
Eric