I am with the AD9361 as part of a Benetel TDD RF card
The Benetel card is connected to a BSC9131 dsp core
I am trying to activate the loopback mode
The loopback mode is described in the register map. They have the following table:
In the table they describe 7 observation points.
My understanding of this table is that the loopback is closed at different points. For example the second observation point in the table 'TX HB2 Output Data (15 Bits)', means that the output of the HB2 filter is connected to the RX HB2 input. The 'TX HB3/Int3 Output Data (12 Bits)' is connected to RX HB3 input, and so on
Additionally I understand that the RX observation points (RX ADC, RX quad cal etc.) are for a different kind of loopback - received samples are re-transmitted by the AD9361
I have a couple of issues with the loopback
1. no matter what observation point I select I always get the exact same output.
2. What is the meaning of the bits in the observation points? I guess it is the number of bits in the looped back samples, but as I said, I see no difference in the results
3. where are the Tx quad cal is located in the transmission chain? is it right before the dac? it is not depicted in any diagram that I have ever seen. to my understanding the DC cal just adds DC to the transmitted samples while the amplitude and phase cal outputs just multiply the samples by some complex number or by some matrix