Re: [Discuss-gnuradio] Changing external reference frequency with USRP2...

[Matt Ettus]

On 08/16/2010 12:21 AM, Ian Holland wrote:
> Thanks Matt
>
> I tried to change to get the external reference frequency to be 36
> MHz, by setting B to 50 (i.e. 0x32) and R to 36 (i.e. 0x24). To do
> this, I modified lines 43 and 85 respectively to the following:
>
> ad9510_write_reg(0x06, 0x32); ad9510_write_reg(0x0C, 0x24);


If you set R to 36 then your compare frequency is 1 MHz.  A setting of B 
= 50 means you are trying to lock at 50 MHz, which won't work.  The 
crystal is at 100 MHz, so you need to use B=100.

This will cause you to be way off in frequency (maybe 100 to 150 ppm). 
It should still function, however.

> However, when I rebuilt the firmware (txrx.bin) and wrote it to the
> SD card, I was no longer able to see an OFDM signal I had been
> transmitting from another SDR at 2.4 GHz. This occurred both when I
> had configured the receiving SDR to lock onto the 36 MHz reference
> (device->config_mimo(usrp2::MC_WE_LOCK_TO_SMA)) And when I configured
> the receiving SDR to use its internal reference
> (device->config_mimo(usrp2::MC_WE_DONT_LOCK))
>
> Have I done something wrong in my modifications? If so, can you
> please suggest what I am doing wrong? According to the AD9510
> datasheet I believe my changes should have been correct.


If it doesn't work with either setting then it is likely your firmware 
is bad.  Check to make sure you are using a good Microblaze compiler.

Matt