For me at least, this is more conceptual, but I am interested in understanding more after reading about the issues? with the uBitx power amp driver and predriver problems.? What are the best practices for designing this portion of a transmitter when it is to cover such a wide range of frequencies?? I imagine it also applies to a monoband radio.
This is what comes to mind based on my limited knowlege and what I've gathered from reading stuff here.
1)Keep amplifier intos and outofs away from each other.
2)Keep amplier gain stages reasonable.? Add more stages instead of upping gain.
3)Pick the right device for the desired frequencies.? Obviously 2n3904's don't work for this application.? Does picking a part with an fT about 40 times the highest desired frequency a safe bet?? Can you pick an fT that is too high (like a npn transistor with and fT of 10 gHz for a 3-30mHz radio)?? I ask this last bit after looking through the digikey transistor offerings...
I suppose any device needs to be tested and tweaked for its application.
4)Keep rf wires/traces away from each other and from the dc path.??
Makes me wonder how the ft817 does hf, vhf and uhf...? I suppose it could be a good exercise to look at how others have done it successfully, like elekraft with the k2.? It will be interesting to see how the QSX does it.
Would making a transceiver optimized for one band and then making transverters for the other bands avoid some of these problems?? I'm thinking of what is outlined in the From Crystal Sets to Sideband book.
-Jeff
AG7NW
