I tried to input EXT LO signal to fmcomms 3 to test the performance of SDR, such as phase noise. I selected Ext Tx Lo command under clocks in IIO, and I also wrote SPI command:
SPIWrite 005,77 // Both Tx and Rx use LO signals coming from Ext. LO
SPIWrite 051,0F // Enable Tx LOGEN but power down Tx VCO, plus Tx VCO LDO, therefore
external supply is needed for Tx Ext. LO; If using Tx VCO LDO for Tx Ext. LO, set Reg050 = 0Eh)
SPIWrite 057,0x // Enable both Tx and Rx Ext. LO (NOTE preserve D3:D0 if desired)
SPIWrite 2A1,F0 // Power Down Tx LOGEN divider
When I changed the frequency of signal generator, the frequency of TX changed. So it seemed that I did the right thing. But, I just changed the TX Attenuation and tried to connected more data, all the signals disappeared. Even I didn't use external Lo signal and reboot the board, I couldn't get any signal from TX channel.
I was wondering if I need to do some other SPIWrite Command to recover all the settings? Or what kinds of SPI do I need to check to get all my settings back?