Concentric Nulling

[Wiltran]

When you add or subtract turns on bucking coil to nullify RX coil, it changes the TX freq. Does anyone know of a good procedure to keep TX freq. at say, 6.7 khz while at the same time properly nulling the RX coil?

[WM6]

When you add or subtract turns on bucking coil to nullify RX coil, it changes the TX freq. Does anyone know of a good procedure to keep TX freq. at say, 6.7 khz while at the same time properly nulling the RX coil?

If TX alone oscillate stable at chosen frequency, you do not need further procedure to keep it at exact frequency during coil nulling. Small changes in nulling are nothing critical. But in need you allways can do some back-changes in TX frequency with condensator in tank circuit.

[Tepco]

When you add or subtract turns on bucking coil to nullify RX coil, it changes the TX freq. Does anyone know of a good procedure to keep TX freq. at say, 6.7 khz while at the same time properly nulling the RX coil?

Probably the best way is to first disconnect C from RX coil, keeping it non-resonant, and achieve coarse null. Only then add C and fine tune for best null. This will prevent interaction of two mutually coupled (if not nulled) LC circuits, affecting TX freq. to some degree, depending on TX oscillator design.

[Wiltran]

Probably the best way is to first disconnect C from RX coil, keeping it non-resonant, and achieve coarse null. Only then add C and fine tune for best null. This will prevent interaction of two mutually coupled (if not nulled) LC circuits, affecting TX freq. to some degree, depending on TX oscillator design.

Thanks Tepco, I will give it a try!