It has been a while since I updated my blog with progress regarding the development of my Irwell HF transceiver and for those who have been following the project, I realize you may find the lack of updates frustrating and I get it!
Now, while it may appear that I have not been working on the project, I can assure you I have and the next blog post will be coming soon.
In short, I have had a frustrating time with the design of the modulator, which has turned out to be a greater task than I envisaged.
Making the decision to include FM as a mode of operation opened up a rather large a can of worms. The microphone amplifier circuits I featured in my last blog post are fine for SSB and AM modulation but not ideal for FM modulation, as they lack pre-emphasis. Also to avoid over deviating in FM mode some form of clipping/limiting is required, then there is the small matter of how to implement FM modulation at the component level.
In the end I decided to generate the FM modulation using a PLL IC and VCO. This was no easy task, as the PLL chip data sheet was a nightmare to make sense of and I had a huge learning curve writing the software to control the PLL IC, I am not a software engineer and my knowledge in this area is limited to what I have taught myself.
After building various prototype circuits and many hours of work, I feel I have achieved my design goal and I am now in the process of finalizing a suitable PCB for the module. Once I get the PCB's back from fabrication, I will build and test one and if all goes well, I can move onto the final few modules needed to complete the project.
I will go into much greater detail when I update the blog.
For now, best 73 from
Andy (G6LBQ)
