HDMI test fixture for TMDS to single-ended SMA for RF testing.
This board is designed to test RF input and output using TMDS signals from the Pynq-Z2 board's HDMI port. It capacitively couples the clock signal for use as an NCO (this is used in a single-ended output/input mode). And it provides two identical differentially-coupled signals for either RF input or RF output.
The RF signals are filtered by a 4th order Chebyshev bandpass filter. The RF is coupled to the TMDS pair via a center-tapped 1:1 RF transformer. The center tap is connected to ground via a 50 Ohm resistor.
The filter is designed for the 2m amateur radio band, but can easily be adapted to other bands of interest. It is important to have at a minimum a low-pass filter with the 2λ at down least -40dB to prevent aliasing.
