RF impedance and resonance.

Posted by Al Sekela (A) on May 3, 2007 at 11:22:30

In Reply to: Can someone explain.... posted by lipmanl on May 2, 2007 at 14:03:43:

Power cords have to be flexible and resist abrasion. These requirements affect their base-band (power and audio frequency) performance. Their geometries also influence base-band noise rejection. RF resonance control is a third aspect of power cord performance. It is not widely understood, but can make the difference between acceptable and unacceptable audio performance.

The AC outlet and plug present impedance changes to RF noise relative to the house wire and power cord impedances. RF energy is reflected by impedance changes ("mismatches").

This makes the power cord, the house wire cable from the outlet to the breaker panel, and even the feed from the utility transformer secondary to the breaker panel, act as separate RF resonators.

Resonance in low-loss objects can take modest inputs and create strong outputs. Consider organ pipes as a familiar example.

Power cords and house wire cable segments are low-loss objects, unless you obtain versions that have RF loss mechanisms built in. Oyaide makes a carbon fiber-jacketed house wire cable that will suppress RF resonances, but it is very expensive. Some after-market power cords are designed to suppress RF resonances, or manage to do so as a consequence of some other design choice. The carbon fiber outlet plates made by Furutech and Oyaide, and the carbon fiber plug bodies on some Oyaide models, also help reduce the RF resonances. Some folks use ferrite beads or clamps, but I find the audio performance of the ferrites to be unacceptable.

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Follow Ups Full Thread

Topic - How about hardwiring Romex from the panel directly to a multiple-outlet box/conditioner? - clarkjohnsen 11:07:24 05/02/07 (20)

Re: How about hardwiring Romex from the panel directly to a multiple-outlet box/conditioner? - MylesJ 17:02:13 05/02/07 (1)

And there we have it! Thanks. nt - clarkjohnsen 07:41:26 05/03/07 (0)

Can someone explain.... - lipmanl 14:03:43 05/02/07 (7)

Radiating high frequency noise - John Swenson 12:29:44 05/03/07 (1)

Thanks! - Al Sekela 11:47:15 05/04/07 (0)

RF impedance and resonance. - Al Sekela 11:22:30 05/03/07 (0)

Re: Can someone explain.... - andy_c 15:00:13 05/02/07 (0)

Re: Can someone explain.... - Stephæn 14:51:08 05/02/07 (2)

Or why does water not come out of the hydrant the same as... - Steve Parry 15:06:19 05/02/07 (0)

Re: Can someone explain.... - lipmanl 14:53:43 05/02/07 (0)

Use good stuff - WinthorpeIII 13:34:08 05/02/07 (1)

I spoke "Romex" generically; the JPS is what's envisioned. nt - clarkjohnsen 07:38:36 05/03/07 (0)

If you're ever in your local Lowe's... - andy_c 12:15:37 05/02/07 (5)

Re: If you're ever in your local Lowe's... - Pooge 14:36:45 05/02/07 (1)

Re: If you're ever in your local Lowe's... - andy_c 14:51:36 05/02/07 (0)

That's because it IS a legal document..... - Bob Rex 13:44:06 05/02/07 (2)

Indeed, the NEC is nothing more than a blueprint recommendation... - AAG 05:38:51 05/03/07 (1)

Re: Indeed, the NEC is nothing more than a blueprint recommendation... - jea48 06:20:58 05/03/07 (0)

Re: How about hardwiring Romex from the panel directly to a multiple-outlet box/conditioner? - maabx 11:56:17 05/02/07 (1)

Neat solution! nt - clarkjohnsen 11:59:50 05/02/07 (0)

Follow Ups

RF impedance and resonance. - Al Sekela 11:22:30 05/03/07 (0)

RF impedance and resonance.

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