Re: [Discuss-gnuradio] USRP2 External Clock

[Kyle Pearson]

Thank you. Running at 100MHz is fine for me, I just have a 100MHz
external clock that I would like to use as a reference for the USRP2.
Could you point me in the direction of where that code is in the
firmware? I took a look and I haven't come across it yet.

Also, could you tell me what the pins labeled Test CLK are? Can they
be used to see the clock after locking it to the external reference?

Thanks,
Kyle

On Wed, Oct 22, 2008 at 5:44 PM, Matt Ettus <address@hidden> wrote:
> Kyle Pearson wrote:
>>
>> I'm aware that the internal clock can be locked to an external 10MHz
>> reference. I take it that there is no way to use an external 100MHz
>> clock instead of the internal clock then.
>>
>
> The internal clock (a very clean VCXO) is locked to the external reference.
>  You have a lot of flexibility as to the reference frequency, as I said in
> the previous message, but you cannot pull the VCXO further than a few kHz,
> and you cannot use the reference as the main system clock.  So there is no
> way, for example, to put in a 120 MHz clock and have everything run off of
> that.  You are basically stuck with 100 MHz unless you are willing to
> solder.
>
> If you are willing to do some soldering, there are pin-compatible VCXOs in
> other frequencies which are available.  The part is the CVHD950 from
> Crystek, and you can get them from Mouser.  They come in the following
> frequencies:
>
>   54 MHz
>   74.1758
>   74.25
>   80
>   100
>   120 MHz
>   122.88
>   125
>
> and possibly others.  Note than anything over 100 MHz may make it hard to
> get the FPGA to meet timing requirements.  Also, the ADC is only specified
> to 105 MHz, but there is a pin-compatible version spec'ed to 125 MHz.
>
> Matt
>
>
>> -Kyle
>>
>> On Wed, Oct 22, 2008 at 4:17 PM, Eric Blossom <address@hidden> wrote:
>>
>>>
>>> On Wed, Oct 22, 2008 at 04:12:07PM -0400, Kyle Pearson wrote:
>>>
>>>>
>>>> I'm wondering if it is possible to connect the USRP2 to an external
>>>> 100MHz clock like the USRP was able to be modified so it could connect
>>>> to an external 64MHz clock. I don't see any place to solder on a SMA
>>>> connector but there are a set of pins labeled Test CLK. Could that be
>>>> used for inputting an external clock or is it just for testing the
>>>> clock output?
>>>>
>
>