Saturday, 31 January 2015

SDR TXRX Block Diagram

As things are slowly getting sorted out, here is the block diagram of the four board SDR TXRX controlled by an Arduino Uno that I have in mind. The boards are useful individually for home constructor projects.

The Universal VFO interfaces with the LCD display and the Rotary Encoder/Button for tuning and band change. It outputs either VFO, VFO and BFO signals for CW transmit or superhet receivers, or /4 frequency I & Q quadrature signals for SDR use. The function depends on the Arduino software program.

The 403020 SDR is a complete SDR receiver with its own input BPF.

The Universal TX is an SDR based wide band transmitter (with around 100mW output). This can be used to generate SSB/AM/CW over a wide range of frequencies. If used stand alone it needs an external LPF.

The 403020 PA includes the LPFs for the three bands 40, 30 & 20m. It also provides the TX/RX switching of the antenna input from the ATU.

Screen Shot 2015 03 22 at 10 05 59

My ideas are coming together, and I must say that they are just ideas today, nothing has yet been made. Other shields considered are a GPS and an Auto ATU. Still its good to go on thinking and studying how to achieve the result. We are considering to make this a club kit project at the Banbury Amateur Radio Society.

By the way, a simple CW TXRX could be made by omitting the Universal TX and driving the PA directly from the Universal VFO. I am including a physical switching link for this on the PA board.


The RF BUS of the system has been increased to 8 pins, giving

- 4 outputs VFO, BFO, I & Q from the Universal VFO

- 2 for RX ground and input

- 2 for TX ground and output

The Arduino UNO connections planned are:

Screen Shot 2015 03 22 at 10 21 55

Where you can see the RFbus signals, and the use of the Ardubi signals D0-D13 and A4, A5 (I2C bus). D2, 4 are used as Interrupt inputs from the tuning rotary encoder, D5 is the band change button, D6, 7 are inputs from a GPS board planned to calibrate the VFO and give timing for WSPR use. D9 is the key or PTT, D10, 11 and for band switching and D12, 13 are for enabling TX or RX.