TRX-DUO based transceiver — pt.1 TRX-DUO board

Transceiver is pretty simple — it’s based on prebuilt modules from «60dbm» and trx-duo board from aliexpress with minor changes.

This post is about trx-duo board itself.

Stock TRX-DUO board:

I modified it with replacing stock clock generator (125MHz) with Crystek CVHD-950 (122.88Mhz) (It also requires to recompile binary for FPGA — redpitaya 122.88 binaries are for Xilinx 7020 chip, but TRX-DUO uses 7010.

As «extclk» is just a caption without any connections the only way to use different generator is just to replace stock clock with the new one:

All in place:

As it’s Red Pitaya clone — i’m using Pavel’s Demin project called «Red Pitaya Notes».

Also RX1 ADC died after few weeks of using — it looks like one input just shorted to the Vcm inside the chip.

I was able to fix it partially. It works with transformer central point on the ground instead of Vcm, with bias above 0volt and with lower sense.

And i just replaced stock LPF filter on RX1 with 7 order chebyshev LPF on the piece of textolite with 0805 smd components. Because it’s pretty complicated for me to work with small stock smd components:

Now RX1 is usable.

I have replacement for ADC, but not sure that i want to put it there. Will see…

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