Strange Ammeter Readings

[Av8r_Sed]

This could be a good application for a snap-on ferrite bead located on the sense lines near the shunt. They kill RF while letting low frequency signals pass. image.jpg

[jiott]

The PTT leads do not pass anywhere near the shunt. The radio antenna cable also does not pass near the shunt. The items/wiring that are near the shunt are: voltage regulator, transponder and its antenna cable, capacitor.

Where do you get the ferrite beads/what brand are they-looks interesting.

[kitfox2009]

G`morning Paul and others

I have Vixen 912UL. All older round gauges. A210 radio and Terra transponder. Avshop after market Lightspeed headsets.

Occasionally I get feedback when on transmit to the point that radio is unusable. I try an old DC and all`s well. Then go back to my Lightspeed and all`s well. When flying last week with a friend and 5 headsets, kept changing them around and everything was fine. (the Bose won, hands down!!). Anyway just wondering if these "ferrets" would help this situation and if so does anyone have an idea as to what type and where I would place them.

Radios and headsets are a total mystery to me and there appears to be quite a bit of knowledge and experience on this forum.

Right now everything is just fine but you never know "it just might start squealing" again. May not happen til next year.

Thanks
Don

[kitfox2009]

That should "ferrite"

[Av8r_Sed]

Ferrite cores are carried by the major electronics distributors such as Mouser and Digi-Key. You can get split cores that can be snapped around an existing cable / conductor or plain cores where you have to thread the conductor through them. Effectiveness can be increased by making multiple turns of the conductor through the core. You probably want to select one that's effective around common com frequencies like 122.8 MHz. Make sure the hole in the ferrite will accommodate the conductors you want to pass through it. For the ammeter application, you might want to pass both sense leads from the shunt through the ferrite.

You'll have to sort out minimum order and shipping prices.

Here's a link to one datasheet: http://www.mouser.com/ds/2/212/KEM_E...-SR-372794.pdf

Note: I don't have any noise issues on my Model III and haven't used these in aircraft service.

[Kurt.A]

I agree with Paul's advise. Another couple ideas you could try would be to twist the wires together that go to the PTT switch. Twisting together allows cancellation of magnetic flux generated by the collapse of the field. Another idea would be to place a schottky diode across the PTT switch which would allow any field collapse to be dispersed within the wiring.

[jiott]

Kurt, my problem occurs from the time I push the PTT switch until I release it. As long as I hold the switch my ammeter readings go wild. Your suggestion would seem to apply only if the problem occurs momentarily when the PTT switch is pushed or released. Do you agree or still stand by your suggestions?

[efwd]

Nice Phil

[jiott]

I installed two ferrite toroids and it didn't make any difference. I have just been living with it; it hasen't seemed to hurt anything.