Magnetic Loop.
 

Hi i have built a .9 meter m l a with a air spaced cap to tune said 2 turn loop, works well as i can null out most qrm, on tx i can get almost 1 to 1.Tuning is very sharp around 10khz on rx even sharper on tx so i fitted a slow rpm motor so i can tune remotely ok the tuning is ok BUT as soon as i connect the dc supply wire noise goes up even without being connected to a power unit (6v battery) the motor and connections to it are inside the loop, so how to remove the qrm being picked up by the 2 core wire to the motor maybe rf choke and caps like a wave trap idea what do others think. by the way the improvement is like chalk and cheese b4 s9+5 with loop s4 will right up details if any interest Mick

Re: Magnetic Loop.
 

Two possibilities:

Noise from PSU/controller coupling into loop

Wire to motor receiving QRM from the environment and coupling it to the loop.

So you need to kill both common mode and differential mode at the loop end of the motor wires. So ferrite cores, multiple turns, and capacitors.

David

Re: Magnetic Loop.
 

Thanks that is just what is happening, yes its noise from the local switch modes etc just could not think how to get rid thank you Mick

Re: Magnetic Loop.
 

Chokes on each leg of the supply lines, and at either side of the chokes, caps from both sides to common and caps across both sides of supply lines.

Basically a Low Pass Filter to pass DC supply but stop RF.