RFI give up

I talked in an earlier post about the RFI from the DC motor in the linear actuator that elevates my satellite antennas.

The RFI is most noticeable on SSB on 144MHz. The FT-847 noise blanker does a good job of reducing it. Without the noise blanker, the RFI is S9. With the noise blanker, it drops to S3. So, it is not a major problem, but it was annoying enough to prompt me to try three things to cure it:

• Covering the motor housing of the linear actuator in aluminium foil shielding.
  
• Adding a 470nF capacitor across the DC supply to the motor.
• Putting series inductors in both the positive and negative supply lines as close to the actuator motor as possible.

The photos below show the last of these as I installed it. The first photo shows the inductors, made from 10 turns of enamelled copper wire on small ferrite toroids. The inductors are soldered to the supply wires that previously connected directly to the motor; the motor has been removed from its usual position on the plastic base that the inductors are "hovering" over. After I soldered the wires from the inductors to the motor terminals, the toroids were pushed down out of the way into the oval pockets you can see in the photo.


The remaining photos show the five screws that I had to undo in the first place to remove the assembly that holds the motor, gears and limit switches. You can also see (top left) the capacitor I added across the supply terminals.


And the results of all this work? Absolutely no difference :-) As I said in my last post, the RFI problem is annoying but so far has not caused real operational problems. So I guess I will learn to live with it.