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Diffstat (limited to 'host')
| -rw-r--r-- | host/docs/res/twinrx_alias.png | bin | 0 -> 53359 bytes | |||
| -rw-r--r-- | host/docs/twinrx.dox | 14 |
2 files changed, 14 insertions, 0 deletions
diff --git a/host/docs/res/twinrx_alias.png b/host/docs/res/twinrx_alias.png Binary files differnew file mode 100644 index 000000000..1be1ca985 --- /dev/null +++ b/host/docs/res/twinrx_alias.png diff --git a/host/docs/twinrx.dox b/host/docs/twinrx.dox index d8dd20f6d..e0d327499 100644 --- a/host/docs/twinrx.dox +++ b/host/docs/twinrx.dox @@ -45,6 +45,20 @@ custom RFNoC FPGA images, but the DDC can be replaced by a custom block as long as it consumes the 400 Msps and produces an aggregate of less than 200 Msps. +Starting with UHD release 4.1, the X310/X300 FPGA images no longer contain a +halfband anti-aliasing filter directly after the ADC when using TwinRX. The +filter was left out because the radio no longer decimates the sampling rate for +TwinRX, instead relying on the DDC RFNoC block to adjust the sampling rate, and +the DSP utilization of the filter was permanent, even when no TwinRX daughtercard +was used. This means the output of the radio block (which produces a 200 Msps +output signal when using TwinRX) contains aliases of the signal. The following +image shows the output of the X310+TwinRX when configuring it to run at 200 Msps. +The center frequency is set to 2.1 GHz, and a signal is applied at approx. 2.13 GHz. + +\image html twinrx_alias.png "TwinRX Signal Aliases" + +Due to aliasing, a mirrored alias signal will also appear at 2.17 GHz. The +statically connected DDC block will remove these aliases. \image html TwinRX_Block_Diagram.png "TwinRX Block Diagram" |
