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To Ross et al: From OP: Household Noise Sources ?
In article ,
"Robert11" wrote: Hi, Any idea how quickly in distance these household noise generated fields diminish to values unlikely to be picked up ? Snip This is a complex question. Firstly to consider is that there is two types of noise sources or ways for noise to find its way to your radio: 1. RFI, radio frequency interference, which is radiated noise. Radiated noise can travel long distance and is an example of the signals you want to receive. 2. EMI, electromotive interference, which is conducted noise. As separate local electric and magnetic fields the energy falls off rapidly over distance. A few feet can make a big difference in noise level. If the problem electronic device is radiating the noise (RFI) then how much it bothers your reception will be determined by how much noise it generates and how efficiently it radiates that noise. Generally the dimensions of the device mean that any radiators in the device will be electrically small and the efficiency the device to radiate noise energy will be poor. The result is most of the noise energy will become localized electric and magnetic fields known as inductive fields as opposed to what is know as a far field EM wave. The radiated EM wave has a special relationship between the electric and magnetic component fields that allow the long distance propagation to occur. The localized electric fields tend to spread out more than the magnetic fields in the low dielectric air and the majority of non metallic house building materials slow them down by tending to bend them but don't stop them. The result is that the inside of most homes are much noisier inside then just a few feet outside most structures. So you can draw several conclusions from this such as that the local noise field energy will fall off rapidly over distance from the noise source. This means that you can reduce noise by moving a portable radio or antenna farther away from the source. Antennas that are sensitive to the magnetic component and not the electric component on the EM noise fields will fare better than an antenna that is an electric field type in the area of local noise sources. A common mode electric field antenna will the worst performing antenna around local noise sources. If the main noise generation is EMI meaning that the noise is conducted down the power cord into the AC mains supply then several things can happen: A. If you plug your radio into the AC mains supply then the noise goes up the radios power cord and is conducted into the radio. B. In addition to this direct conduction if you have an external antenna connect by coax cable this noise can be further conducted on the outer shield and then transfer to the antenna as common mode energy. C. Noise that starts out as EMI in the mains AC supply now has found larger radiators, which is the wiring in your house and then can radiate more efficiently becoming RFI. "C" can be an especially insidious problem to solve. Strategy to follow to reduce local noise: 1. Put as much distance as you can between the radio, antenna and the local noise sources. 2. Use an antenna type sensitive to the Magnetic component of a EM wave. 3. Use RF chokes on noise source device power cord and other cables. 4. Turn off and actually disconnect electronic noise sources. 5. Identify troublesome noise sources by unplugging or disconnecting everything in the house and turn them on one at a time after a scan on the radio. 6. Use chokes on the coax to the antenna or choose a lossy RF path for the coax such as putting it in the ground on its way to the antenna from the house. 7. Locate external antennas away from power lines, the house and neighbors homes or other noise sources. -- Telamon Ventura, California |
#2
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To Ross et al: From OP: Household Noise Sources ?
Telamon wrote:
2. EMI, electromotive interference, which is conducted noise. As separate local electric and magnetic fields the energy falls off rapidly over distance. A few feet can make a big difference in noise level. I think we're confusing EMF (Electromotive Force), also known as Voltage with EMI (Electro magnetic interference). Good posting, though... mike |
#3
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To Ross et al: From OP: Household Noise Sources ?
In article _QBAf.97693$AP5.14846@edtnps84, m II wrote:
Telamon wrote: 2. EMI, electromotive interference, which is conducted noise. As separate local electric and magnetic fields the energy falls off rapidly over distance. A few feet can make a big difference in noise level. I think we're confusing EMF (Electromotive Force), also known as Voltage with EMI (Electro magnetic interference). Good posting, though... Yep, sorry about that EMI definition. -- Telamon Ventura, California |
#4
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To Ross et al: From OP: Household Noise Sources ?
Yeah sure,shutting everything off in your house will improve radio
reception.But,I am not going to shut down my house for any radio(s) in this World.Cat Ballou movie (I went and saw that movie here in Jackson when it first came out,I was home on a three day leave from Fort Hood,Texas) is just now starting on Radio tv and I better get me happy arse back over yonder and see if that divorced woman in Petal,Mississipi is drumming me up. cuhulin |
#5
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To Ross et al: From OP: Household Noise Sources ?
Telamon wrote:
m II wrote: Telamon wrote: 2. EMI, electromotive interference, which is conducted noise. As separate local electric and magnetic fields the energy falls off rapidly over distance. A few feet can make a big difference in noise level. I think we're confusing EMF (Electromotive Force), also known as Voltage with EMI (Electro magnetic interference). Yep, sorry about that EMI definition. Electromotive interference is EMI from a locomotive plant in La Grange, IL. -- If John McCain gets the 2008 Republican Presidential nomination, my vote for President will be a write-in for Jiang Zemin. |
#6
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To Ross et al: From OP: Household Noise Sources ?
In article ,
clifto wrote: Telamon wrote: m II wrote: Telamon wrote: 2. EMI, electromotive interference, which is conducted noise. As separate local electric and magnetic fields the energy falls off rapidly over distance. A few feet can make a big difference in noise level. I think we're confusing EMF (Electromotive Force), also known as Voltage with EMI (Electro magnetic interference). Yep, sorry about that EMI definition. Electromotive interference is EMI from a locomotive plant in La Grange, IL. Funny! -- Telamon Ventura, California |
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