The ThinkRF RTSA's Direct Digitization (DD) mode supports 50MHz IBW of the baseband from the external RF IN. Its center frequency is at DC (or 0 Hz). Thus, in this mode, one cannot do frequency tuning; however, the embedded DSP's frequency shift feature could be used to move this center frequency when needed.
For DD mode, use the following commands:
- :INPUT:MODE DD
- Optionally, :FREQ:SHIFT to move the center frequency (see the product's Programmer's Guide for the usage details). Note that this feature will result in the I-only DD data output to become {I,Q} output. Decimation would, then, be needed with this usage to narrow the BW of interest & avoid IQ artifacts introduced by the frequency shifting. See Table 2 of the Programmer's Guide to understand what I/Q data format is provided for each RFE mode and when any DSP is applied, including the handling of the IBW.
Do not use :FREQ:CENTER when already set the DD mode, this will cause a SCPI error. Otherwise, all other commands applied to other RFE modes could be used for DD as well.
Note also, when *RST is used with DD, it takes about 2 seconds for DD data to settle. Hence, avoid reset in this mode if possible.