How to configure AX-RADIO Lab to generate GMSK with short preambles


I am struggling with AX-RADIOLAB with GMSK modulation parameters which I tried to derive it from FSK ones, because the (G)MSK option is absent from the dropdown list in the GUI. I also noticed a magic trick to allow more options in the dropdown list, but only MSK has appeared so far and unfortunately the preamble length is very long and cannot be changed from AFC/Oscillator parameters.

So basically my question is, what is the recommanded approach to get GMSK modulation at 100Kbit/s with 16 bits preambles and 24 bits sync word?

Thank you

Hello, thanks for your post and welcome to the Onsemi Community Forum.

You are right, in order to select MSK modulation in the GUI one needs to first to insert ‘1962’ inside the period text field.

In order to control the shaping you should manually program the FREQSHAPE field of MODCFG register either via the “Edit Register” button or directly in your code. The values are shown in the AX5043 Programming Manual (note that 00 = Unshaped):


Thanks for the confirmation, I was doing exactly what you proposed. So now, I have one remaining question

I need to select between XTAL/OSC for my new design in order to comply with a fixed preamble length of 16 bits. But it seems that the current GUI in MSK mode does not allow that because AFC/oscillator precision cells cannot be modified ?

Also, the associated minimum preamble is constant and set to 266 when using unencoded. :slightly_frowning_face:

Is there a proper way to configure short preambles with GMSK?

Thanks for your help