Yes, you can do that.
In the analog VFO, the voltage on the varicap determines the frequency. So reversing the voltage polarity of the tuning pot will "reverse" the frequency coverage; it will not change the span. You can do it either way with DDS software. In effect you are simulating the analog VFO.
Ordinarily (and in the other 20m BITX) RF = IF + VFO. With an IF of ~12 MHz,the VFO should be ~2 MHz.
Look at your figures. Both 19.998 and 4.998 are VFO frequencies. The IF is 11.998 MHz. Work from there.
john
AD5YE
---In BITX20@..., <chase8043@...> wrote :
John
I had noticed the reverse tuning of the Bitx40, but adjusted the sketch to fix this.
I also made a second sketch to work on 20M, using a 18.998600 MHZ VFO. So 18.998600 - 4.998600 = 14.0. Is this correct? Will I be on the correct sideband?
73 Ken
