60/120 Hz magnetic fields

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gar

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Ann Arbor, Michigan
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EE
180602-1527 EDT

Do you look for stray 60 Hz originated magnetic fields?

If so, then what initiated your search? What magnitude in mG have you found? What mG level do you consider a problem and why?

Have you looked at waveforms? Is harmonic content a problem in the measurement? Have you looked close to fluorescent or motor or power supply type things that may have an iron core inductor in them?

.
 
Would like to contribute to your topic gar, however about the extent of my testing with magnetic fields and noise is limited to noticing quite a bit of buzz on a toner probe, and dutifully abiding by TDMM specs of keeping communication cables at least a foot away from such sources... I have traced noise on phone lines to cables run right over top of fluorescent fixtures.

Perhaps you might know why twisted-pair cabling does not reject this noise, however shielded, unbalanced cable AKA coax is more or less immune to such interference.
 
I have significant magnetic fields in my home due to a set of medium voltage transmission lines that run up an easement next to my property. I had the utility come out with their gear to analyze it some years ago; they confirmed it, but I don't remember the numbers they told me. It's enough to make the single coil pickups in my Strat howl like banshees when I plug into a high gain audio circuit and to distort the color on the old 32" CRT TV I used to have in my living room.
 
180603-0755 EDT

Russs57:

Coax or Beldfoil (or other equivalent shields) shielded cable will greatly shield the wires internal to the shield from electric fields external to the shield.

Magnetic fields at low frequencies will penetrate non-magnetic shields like copper or aluminum. So for low frequencies conductive shields do not prevent magnetic field induction. Beldfoil and the like is an aluminum foil anodized on one side so that when totally wrapped around the wires being shielded that a shorted turn is not created. Aluminum oxide (anodizing) is a very good insulator.

The intensity of variation of a magnetic field over a spatial area and the spatial distribution of a pair of wires will determine the magnetically induced voltage between the two wires in a wire pair.

I will get back to this later.

.
 
ggunn said:
I have significant magnetic fields in my home due to a set of medium voltage transmission lines that run up an easement next to my property. I had the utility come out with their gear to analyze it some years ago; they confirmed it, but I don't remember the numbers they told me. It's enough to make the single coil pickups in my Strat howl like banshees when I plug into a high gain audio circuit and to distort the color on the old 32" CRT TV I used to have in my living room.
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and you haven't wrapped your home in aluminum foil?


















:D
 
180603-1124 EDT

Besoeker:

But I am interested in seeing whether I can see 50 Hz buried in the mud (in a signal sense) either as a magnetic field, or as a conducted current in the earth.

My attempt would be with a correlation detector and a long integrating time constant. I doubt I will see anything. I expect background noise to be too high.

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gar said:
180603-1124 EDT

Besoeker:

But I am interested in seeing whether I can see 50 Hz buried in the mud (in a signal sense) either as a magnetic field, or as a conducted current in the earth.

My attempt would be with a correlation detector and a long integrating time constant. I doubt I will see anything. I expect background noise to be too high.

.
Click to expand...
My attempt was at levity.............
Forgive me.
 
gar said:
180602-1527 EDT

Do you look for stray 60 Hz originated magnetic fields?

If so, then what initiated your search? What magnitude in mG have you found? What mG level do you consider a problem and why?

Have you looked at waveforms? Is harmonic content a problem in the measurement? Have you looked close to fluorescent or motor or power supply type things that may have an iron core inductor in them?

.
Click to expand...

Calculate the transfer function of the buried cable and calculate both the electric and magnetic field from that. Hyperbolic trig functions. Or measure with Rogoski coils.
Part of job used to be determining pickup of buried cable form NWE EMP fields. Calculated currents in buried cables using burial depth, soil conductivity, shielding, etc.
Took 20 some columns onf excel spreadsheet to do hyperbolic trig on complex functions, probably easier on matlab or similar.
 
mbrooke said:
Forgot about that :slaphead:
Click to expand...

In a related story...

When I was in college the first time back when dinosaurs walked the earth, someone once snapped off my car's radio antenna. My GF and I used to park out by an on campus lake (we called it "watching the submarine races") and listen to the radio. My favorite late night station was KAAY in Little Rock, a clear channel station that I could usually listen to from Baton Rouge where we were, though the reception wasn't great.

Anyway, with that stump of an antenna there was no way I could pick it up, so one drippy night I got a length of wire, stripped both ends, twisted one end around the antenna stump and the other around my tire iron, and drove the tire iron into the wet ground next to my car. KAAY came in so strong it sounded like it was 4, not 400, miles away.

Anyone else remember Clyde Clifford and his Beaker Street radio show on KAAY from the late 60's and early 70's? A lot of the music I still love today I heard there for the first time. All we had locally in those days was Top 40 AM radio. Beatles and Stones, sure. But Led who? Fleetwood what?
 
60/120 Hz magnetic fields

ggunn said:
In a related story...

When I was in college the first time back when dinosaurs walked the earth, someone once snapped off my car's radio antenna. My GF and I used to park out by an on campus lake (we called it "watching the submarine races") and listen to the radio. My favorite late night station was KAAY in Little Rock, a clear channel station that I could usually listen to from Baton Rouge where we were, though the reception wasn't great.

Anyway, with that stump of an antenna there was no way I could pick it up, so one drippy night I got a length of wire, stripped both ends, twisted one end around the antenna stump and the other around my tire iron, and drove the tire iron into the wet ground next to my car. KAAY came in so strong it sounded like it was 4, not 400, miles away.

Anyone else remember Clyde Clifford and his Beaker Street radio show on KAAY from the late 60's and early 70's? A lot of the music I still love today I heard there for the first time. All we had locally in those days was Top 40 AM radio. Beatles and Stones, sure. But Led who? Fleetwood what?
Click to expand...

Same here...only the submarine races were on the Mississippi.

Beaker Street was awesome!

I’m about 350 miles from Little Rock. Couldn’t get KAAY until it got dark - which is the best time time to watch the submarine races anyway.
 
retirede said:
Same here...only the submarine races were on the Mississippi.

Beaker Street was awesome!

I’m about 350 miles from Little Rock. Couldn’t get KAAY until it got dark - which is the best time time to watch the submarine races anyway.
Click to expand...

Remember Jaime Brockett's The Legend of the USS Titanic? Clyde used to play it pretty often.

You gotta let it OUT, Cap'n! :D
 
ggunn said:
Remember Jaime Brockett's The Legend of the USS Titanic? Clyde used to play it pretty often.

You gotta let it OUT, Cap'n! :D
Click to expand...

I don’t remember that one....unfortunately that’s not the only thing I don’t remember. According to what people tell me, I’ve forgotten plenty!
 
kwired said:
and you haven't wrapped your home in aluminum foil?
Click to expand...

CaHv9WH.jpg
 
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