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Author Topic: Air cleaner birdies -- ferrites on AC feed?  (Read 647 times)
VA7CPC
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Posts: 2357




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« on: October 25, 2003, 01:51:05 PM »

I've just tracked down the source of birdies every 20 KHz through 80/40/20 meters.  

It is an electrostatic precipitator (fancy air cleaner, by Lennox) attached to the furnace. It uses high DC voltage, and gets it from a 20 kHz p/s.   It was making all the house wiring "live" -- a portable SW radio picked up the birdies from every wall switch.

I'd like to choke the birdies, by winding the 117v AC feed wires around 3 ferrite toroids, inside the junction box that powers the unit.

a)  Is this safe?

b)  Will it be effective?

Thanks.
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KA5S
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Posts: 229




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« Reply #1 on: October 26, 2003, 01:04:19 PM »

As long as you do not damage any insulation, it should be safe. I won't say it will be effective.  The "usual" ferrite EMI beads have a permeability of about 100 or so and an impedance around 80-120 ohms at 100 MHz. Impedance (and EMI attenuation) is MUCH lower at 80 - 10 meters. Winding extra turns does increase the impedance, of course.

See if you can find higher permeability ferrites made for supressing the HF spectrum.  As one example, a Steward type 35 material bead 35A2024-0A has a single pass impedance of 93 ohms at 4 MHz.

This is unfortunately not a CHEAP ferrite, as it requires special attention to make. It also bears mentioning that different ferrites have different mechanical properties. Treat them all as fragile objects (which thay are; they ARE ceramic). Some are more fragile than others. And not all ferrites are insulators.

Disclaimer: I have no interest in Stewart Corporation; I mention their product here simply because it is one for which I have data.

Cortland
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N8IWK
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Posts: 80




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« Reply #2 on: November 05, 2003, 01:55:47 PM »

I use ferrits for rabbit hunting, and I must agree they will gnaw their way through just about anything, including the insulation on electrical wiring.

I also hunting birdies on occasion, but that's before rabbit season opens.

Smiley  73's
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K1CJS
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Posts: 5884




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« Reply #3 on: March 16, 2004, 11:59:58 AM »

There's always one or two in every crowd.  BTW, don't you know that ferrits love birdies?  That's why ya gotta keep 'em separated!!  ;-))
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