Re: More RFI filter testing...donuts
This is an excellent technique. I use the exact same blue ferrite toroids.
However, I wind a "bucking" choke. I wind a bifilar coil with each adjacent
pair of wires with opposed currents. I use #12 cu insulated wire for ~
11-12 opposed pair turns (total of 22-24 turns). Smaller guage wire and
more turns could be even more effective. I use one choke on each HV
tranformer secondary lead. I also put a protective SG to ground from each
secondary lead bushing. These SGs very rarely fire.
As a test, discharge a low voltage cap across a small resistor and scope
across the resistor. Next fire the same cap and resistor in series with the
above choke. There is a huge decrease in RFI/EMI and there is cancelation
of inductive kickback due to magnetic flux cancelation of common mode
I haven't tried it, but these chokes could be placed on both sides of the
main gap to try and eliminate the high gap transients.
BTW, what harm do these high transients cause? Could they possibly be
helpful in disruptive TCs?
Bifilar common mode toroidal chokes are commercially available from Johnson
Shop Products for under $2.00 each.
> Original Poster: gweaver <gweaver-at-earthlink-dot-net>
> Try this, they work great for me. Get 2 ferrite donuts, mine have a 1.25"
> diameter hole in the middle and they are 2.75" diameter on the outside, 1"
> thick. I wrap 40 turns of #14 copper insulated house wire on each donut.
> Be sure to use insulated wire. A piece of wire about 10' to 12' long will
> give you 40 turns. I leave about 12" of wire sticking out on each end for
> hook up. I use these on all my coils.
> Gary Weaver