Re: Audio bandwidth between the product detector and VOL-H

Evan Hand

I am not the expert on the frequency response of the audio sections of the uBITX, however the preamp should be able to handle the higher frequencies.  The issue I am sure that you will have is the transmit side.  The same BFO and product detector are used to create the transmitted signal that then goes through the SSB filter.  You will either have to use the DSP to transform the mic audio to the correct frequency so that the product detector mixer than adds the correct carrier or change the BFO in the Nano program when transmitting.  You could do some audio compression algorithms for that, it will require a second DAC or relays to feed the current mic preamp.

My question back is why not just do the DSP at the current audio frequencies?  There are audio DSP filters that can be bought to lower the bandwidth to a couple of hundred hertz for CW, so it has been done.  There are also add on boards with higher processing capabilities that can be reprogramed to what you might want to do in the DSP.  One that comes to mind is the JackAl board, though this is no longer available from QRPGuys.  There is also the Teensy upgrade to replace the Nano.  This would give you extra program and I/O space if you want to play there.

My thoughts.  WARNING, they could be wrong.

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