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From: | Matt Ettus |
Subject: | Re: [Discuss-gnuradio] USRP2 External Clock |
Date: | Wed, 22 Oct 2008 14:44:14 -0700 |
User-agent: | Thunderbird 2.0.0.16 (X11/20080723) |
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 125and 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?
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