g0kao
commented
10 months ago A bit of apologising on my behalf, but I had to find this document (https://www.vu2ese.com/index.php/2022/07/20/the-sbitx-the-sdr-for-the-homebrewer/) via the the forum and only then after raising the audio headset related issues I was pointed to this embedded within a different discussion. I have also just noticed the wiki link from the home page of the forum to point to lots of info, what would be really useful is to have a simple readme on the this gitbhub project home page that points users to the wiki page of the forum https://groups.io/g/BITX20/wiki, that way if users come to the github page they see the link to the documentation that is available in a central location. I still have to determine the rationale to connect the microphone in the way it has so will leave this open until I find the info I am looking for in the documents found . The audio quality in and out of the radio is not good and thats what I want to solve if I can from a more usability perspective.
There may be a valid reason for the way Audio I/O is connected to the WM8731 pins in the SBITX V3, however I can't find a reason why those pins were chosen when I look at the WM8731 Datasheet (http://datasheet.elcodis.com/pdf2/88/68/886817/wm8731.pdf) and a sample implementation diagram (https://download.mikroe.com/documents/add-on-boards/click/audio-codec-proto-board/Audio%20Codec%20Board%20-%20PROTO_v102_Schematic.PDF), compare these to the SBITX v3 production schematic (https://github.com/afarhan/sbitx/blob/main/sbitx_v3_production.pdf) there is a clear difference.
This difference may explain the low mic gain issues in particular that have been reported in the forum.
The data sheet and the example diagram show the microphone circuit connected to pins 17 and 18, used also to provide bias for the microphone The SBITX diagram shows the microphone circuit connection to pins 19 and 20 instead.
I haven't taken the board out to trace it through yet as I wanted to find documentation to help me identify where the audio routes are from a circuit perspective and not a software perspective as the software approach is dependant on the hardware approach to work properly together.
There may be a valid design reason for the approach taken, if that is the case please document it, if not then perhaps you need to document how this should be fixed for all those that have purchased this radio to address this problem because basically the radio is not really consistently usable in its current state for SSB modes of operation as delivered.
There may also be a need to review the physical audio output route too to ensure that is correctly wired as intended for SSB modes of operation. It appears that the digital modes side of the radio works ok, I have had many FT8 contacts though relied on external software to reliably operate on FT8, but that is not good for purchasers who wish to use phone modes of operation as well as digital with this radio.
All this has stemmed from the need to improve usability by providing the capability to use USB or Bluetooth headsets that many have raised.
Paul G0KAO