My first real on the books job was at a medical school. One Monday morning we came in, fired up the equipment, I went to the psych department to prepare for a psych evaluation and the control room asked me "How do color bars look up there?"
"Perfect."
"Um...we have a problem, come down and take a look."
So I did.
NTSC has about a 4.0MHz bandwidth [nothing much above 3.58 but you need some slop not to trash the waveform, oh God how I hated NTSC]
The waveform was odd, really odd, setup wasn't 7.5, color burst wondered around like a drunk.
Being the newest employee, "Terry go trace the coax."
Oh the joy of crawling in places no one had been since they wired the building....
I found about 200 feet of our coax missing and replaced with zip? cord.
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Zip cord has something like 100~130 ohm impedance, depends on the number of strands, insulation plastic,? color, spacing, phase of the moon. 75 ohms to call it 115 ohms might not be horrible for a transmitter with a transmatch, but wow it sure trashed the video.
We never found out who stole our coax and had to replace about 500 feet because you couldn't splice in that narrow a space and the coax had become entangled with the then new phone system wiring.
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One day we were doing a production and suddenly ignition impulse noise appeared in the video monitors.
Being a biker I recognized the pattern as a single cylinder motorcycle so I ran the 400 feet to the exit and sure enough there was some Honda CB200 idling. I suggested he move before the cops busted him because he was in a no parking zone (sidewalk) and campus cops had a real hatred for bikers in general and lived to punish those of us who made mistakes. She left and the EMI was gone.
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My best guess violates the inverse square law. I believe the magnetic pulse, not RF EMI, from the ignition coil radiated a strong enough magnetic pulse to get in our system. Yea I know, the magnetic field would have to have been strong enough to control nuclear fusion. Perhaps the magnetic flux was induced into the?
steel I-beams and traveled that way. Except I never could get the math to work. A physics professor told me I had to be mistaken about the EMI source. Needing a passing grade I let him believe what he wanted.
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I still have trouble believing a motorcycle could produce such powerful EMI. This would have been July 1973, I left in August to start college.
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