USB should be easy enough. ?
Ashhar has suggested easy hacks to hit other bands, and USB will be necessary for 20m. ?The obvious thing is to move the BFO oscillator to the other side of the crystal filter passband?by adjusting L5, C102, C103. ?The Si5351 has a second unused PLL which could be pressed into service as a BFO oscillator fully under the control of the C program on the Raduino, though performance would likely suffer a bit due to crosstalk between the two Si5351 channels. ?On the plus side, using the Si5351 for the BFO could reduce circuit complexity, perhaps removing Q10 and Q11 entirely. ?(Likewise, the Si5351 allows much of the analog VFO circuitry to be removed.)
Currently, the VFO operates at 5MHz for an operating frequency of 12-5=7MHz. ?If you leave the crystal filter and BFO oscillator where they are and adjust the VFO for 12+5=17MHz,?this should also give USB operation. ?The analog VFO would not be very stable at 17MHz,?but the Si5351 will do fine. ?So switching to USB operation again becomes just a matter of the C program that controls the Si5351.
I'm hoping for something better for CW ops than whistling into the mike. ?The Raduino will likely be used to generate a pure sine wave at 1khz or so, using pulse-width-modulation from one of its counter-timers, and an external RC low pass filter. ?The pwm from the Raduino can change at the start and end of each element for key shaping. ?Some scheme for putting the IRF510 into class C would make CW operation more efficient. ?Adding an XOR gate in there somewhere (at the BFO or VFO?) might make PSK31 transmissions easier to generate from the Raduino. ?A vague possibility we might even decode PSK31 on the Raduino, though a 32 bit processor would be a much better choice. ?(Google "oddwires stm32f". ?Or perhaps a bluetooth module, have an Android smartphone do the decoding?)
Plenty of other ways to generate a CW carrier, though key shaping is not always trivial. ?For example, could use the third output from the Si5351 to drive the final amplifier pretty much directly, shutting down the BFO and VFO Si5351 outputs, keying the dots and dashes by enabling and disabling that third Si5351 output. ?Key shaping might be a matter of messing with the same bias control into the IRF510 that allows us to run in class C mode.
The above is all speculation of course. ?I haven't actually done any of it.
Jerry, KE7ER
---In BITX20@..., <donfrasher@...> wrote :?
? ?1. ? Is this LSB only? ?
? ?2. ? Is the new BITX40 cw capable? ?
?...
? ?6. ? Will this new version be frequency stable enough to use PSK??
