Ion Petroianu, VA3NOI
I sort of fixed the problem.
First I found my offset (-150Hz). That means for a signal of 7.125MHz I had to adjust at 7.12515MHz for zero beat.
Then load the sketch into Arduino IDE and look for the BFO frequency (2 instances) and substract 150 Hz from the value, so my sketch now reads:
#define INIT_BFO_FREQ (1199785L)
unsigned long baseTune = 7100000L;
unsigned long bfo_freq = 11997850L;
Compile and upload and everything works fine, no calibration required.
I have used KA7OEI's sketch to get the extra digit of resolution and avoid the flickering of the last digit.