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Hi Ashhar,

After solving some hardware issues on my little WM8731 board I finally made it work, first with the alsa-utils then with sbitx software itself, hence a little "eureka" for this successful proof of concept.?

The WM8731 chip is indeed rather touchy (I had some bad experiences in the past driving it from a STM32 chip) and since its internal registers are write only, there is no way to check their content.? Luckily, the series resistors in the I2S and I2C lines proofed quite helpful.? Further, it took me a while to understand that the Si5351 is controlled by its own soft I2C bus.? Now the vfo and bfo generator module is also functional.? See photo 6177, the toroids (2/1 rf transformers) in the clock lines are an attempt to mach de outputs of the Si5351 to 50Ohm for the mixers.?
Finally, I was able to "repurpose" an home build receiver front end (from a previous project) out of my junk box to complete the sbitx hardware, at least as a receiver.? This module (see photo 6178) contains a 30MHz LPF, a SBL-1 type mixer, a rf amplifier, a 45MHz 4 pole crystal BPF (Golledge 45G15B1), a 2nd rf amplifier and a 2nd SBL-1 type mixer.? The output of the 2nd mixer is provisionally send directly to the line input of the WM8731.? The overall gain of this front end is about 10dB, too little for the work (I will later add some amplification at 24kHz).? Also the 45G15B1 is not ideal for this application (the 15kHz bandwidth is too small and stop bands do not fall fast enough), but it will do for this proof of concept.?
See photo 6176 for a complete view of the set up, not very practical using the RasPi-400 ?.?? See photo 6175, a screenshot with the spectrum and waterfall when injecting a -60dBm RTTY signal at 7053kHz, a really fantastic view !.?
The WM8731 annex Si5351 board is fully powered from the Raspi-400 (5V & 3.3V), the front end is powered separately from a 12V source.? Again it it is just a proof of concept.?

I didn't modify the sbitx software (yet), safe for changing the bfo frequency to 45024000. I intent to further hack the sbitx software step by step wise so that it fits my purpose, i.e. having a headless transceiver. I'll keep you posted.?
Obviously I do not intend to keep the SBL-1 mixers and 45G15B1 filter in a final design, I will rather wait patiently for whatever hardware will be made available.? Though I may decide to design my own hardware version of the sbitx. ??

I attempted to run this setup on a RasPi-Zero, it does not work.? A cw signal comes out like that of a broken school bell, i.e. some 10ms of tone followed by 20ms of silence and so on.? Obviously the RasPi-Zero is not powerful enough to run the full sbitx software, a bit astonishing, the RasPi-zero being reputed for handling 250MFlops.? Possibly it may handle a slimmed down version of the sbitx with e.g. no gui.? The benefit of using the RasPi-zero i.s.o. de RaspPi-4 is its power dissipation, less than 1W versus more than 6W.?

Many thanks again for publishing this brilliant design which enables us to be creative in SDR, at least at the surface of it.

73 Jean / ON4JRT

Op 29/07/2021 om 03:09 schreef Ashhar Farhan:

Congratulations in the hack. I forgot to document the second card. I add a virtual cable to enable wsjtx or fldigi to run on raspberry pi. You will have to execute "sudo modprobe snd-aloop" to set it up.?

I would first try running other sound apps (I just run youtube videos on chromium) to see if the sound is working?correctly.

Finally, I must warn you, the wm8731 i2c is very finnicky. As a result, I moved the Si5351 to use a separate pair of digital lines and I do the i2c protocol by manually turning the bits on and off. You can see this used in i2c_bb.c and si5351v2.c.

It would be lovely to see how the system works as a build outside my own shack.?

I also had to move the si5351 off to the mainboard to cure some spurs, but that is probably my slopping wiring.

How are you powering the boards at 5 volts?

- f

On Thu 29 Jul, 2021, 12:33 AM Peter McCracken, <peter.mccracken@...> wrote:

Hi Ashhar,

Why did you switch from 27Mhz to 40Mhz may I ask ?

Thanks!

Best regards, Peter.