Jason Hsu wrote:
Yes, this is related to the noise cancelling device described at
http://www.geocities.com/g4lna/noisdes.html
I'm trying to figure out if I can substitute type 61 or type 43
ferrites for the transformers, because I have these ferrite ring cores
but I do not have the iron powder toroids. Also, using type 43
ferrites would allow me to use fewer turns. (That 160m/180m
transformer requires about 50 turns!) From my experience with
high-power RF transformers, I know that iron powder toroids are less
vulnerable to core saturation and excess heating.
The phase shifter and the amplifier in the noise cancelling device do
NOT work with high power levels like a transmitter, tuner, or
SWR/wattmeter would. So if core saturation and excess heating are not
an issue, is there any particular reason I MUST use iron powder
instead of ferrites?
Jason Hsu, AG4DG
The main positive quality of powdered iron cores is their high
saturation flux. The dispersion of iron in a nonconductive matrix
also gives them low eddy current losses. But if you don't need the
saturation flux (which is usually the case for inductors that are not
carrying a large DC current) then you can substitute a ferrite core
with an air gap.
The ferrite core will have some eddy current losses (dependent on the
bulk conductivity) and hysterisis losses (depending on the BH loop
area), but you can keep both of these arbitrarily low by increasing
the air gap and the turns count. Type 61 has a very high bulk
resistivity, but both type 43 and type 61 have pretty big BH loop
areas. Have you got any of those type 43 split cores that are clamped
around wires to suppress EMI? With a small air gap, they make pretty
good RF inductor cores.
--
John Popelish