One of the approaches we are considering for OpenBTS is to use a VCTCXO with the control voltage taken from one of the D/A outputs of the FPGA, with LOTS of low-pass filtering, of course.

This would not give a wide range of frequencies, but would allow precise frequency calibration through the existing libusrp APIs.


On Sep 28, 2009, at 9:00 AM, Tim Pearce wrote:

In terms of integrating more tightly with the USRP/GnuRadio

You could (maybe) just use the SPI pins and one of the digital IO lines as the enable (the ATMega8 running as a slave)

That way theres functions to communicate with the chip already built in you just need to define the various commands etc? 

Tim.


David A. Burgess
Kestrel Signal Processing, Inc.