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Residential RFI Antenna All Around You

residential rfi antenna

Household wiring is a near perfect residential RFI antenna. It combines conducted and radiated paths to drown out your shortwave receiver. 

Recently, I wrote about the importance of filtering RFI before it gets conducted by your household wiring. My reason for saying this is important and a bit depressing.

Your house is one big residential RFI antenna. Same for your neighbor’s house. In fact, your whole neighborhood is essentially one gigantic residential RFI antenna. By historical accident, except for some safety grounding, household wiring contains no EMI mitigation and actually spreads it around like wildfire.

Electromagnetic radiation is created by electrons accelerating or decelerating in a conductor. This rate of change is driven by several things. First, sine wave signals accelerate or decelerate currents all by themselves. Second, if a conductor is curved, bent, broken, terminated or looped, these typologies change impedance which also effects electron flow.

Your house contains maybe 500 meters of household wiring running through walls and ceilings. Typically, these conductors are in 10 to 30 meter lengths. Any wire will start to radiate when its length exceeds 10-15% of a wavelength. So the shorter10 meter wires start to radiate above 3 MHz. The longer runs start to radiate RF at 1 MHz.

Near-field coupling of RFI takes place near the wires due to reactive coupling (capacitive or inductive.) At greater distances, typically 5 to 50 meters from the wiring, radiation is the dominant path as the EM wave enters the far field. You will find this to be true across MF and HF bands.

Residential RFI Antenna – More Details

So, even within your house, far-field radiation starts. Even if you have an antenna on top of a 50 foot tower, it will receive radiated RFI from your house. Same with all your neighbors, whose homes are residential RFI antennas sending signals to your antenna.

In the far field, radiated EMI waves become planar. With greater distance, they become more like point sources. This is why noise cancellers like my ANC-4 are so effective at reducing RFI from outside my house. You can do spatial filtering with two antennas and phase-cancel the noise.

But inside your house, or even between your house and nearby antenna the interfering signal is too diffuse for spatial filtering. Similarly, rotating your antenna may not make a difference. Using indoor antennas, or dipoles strung along eaves-troughs just make RFI reception worse.

So, you should use filters to prevent EMI from getting conducted along household wiring in the first place. This is probably the most important prevention measure. Here is a video demonstration of mains filtering to reduce residential RFI antenna effects.

Typical RFI conducted voltages on your power lines in the house are 1 to 10 millivolts. Sounds small, but these signals are strong enough to create S9 radiated emissions at 10 meters distance.

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