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September 23rd 03, 02:24 AM
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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 |
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