A few thousand amps D.C. in conductors about 4 metres apart can do wonderful things to nearby CRT television monitors and pickup tubes. The return conductors rails should not be in multiple contact with earth, but faults can occur and remain unnoticed until someone complains that they are getting several volts difference along an 'earthed' wire (or the foundations of a steel-framed building have just been eaten through).
That was more likely to be signalling currents than power.
I presume you are working with RF. Is there an RF equivalent of dBu, based on voltage without reference to impedance?
I can never keep my dBm... etc straight, so my son wrote this utility for me....
Just put a "CE" sticker on it and be done with it. ;-)
I have a pair of 12/14 AWG strippers that cut the outer as well as inner insulation (one pass for each). Basically, it just nicks the outer insulation, all the way around. Then you just pull the end and the outer insulation just slides off on the paper (sometimes the paper is left but usually not). They're great for electrical work (I'm just doing my basement now - 50-60 duplex outlets and a couple of dozen light fixtures).
Try them on some without the paper, and see how they work. :(
I've never seen Romex without the paper; either paper.
I have. It was old and had no brand name, only AWG markings. I've see pieces of AWG 14, 12 & 10. The jacket was bad on all of it. I ripped it all out & ran conduit, then pulled new wire in places I wanted outlets. All the outlets along the fences were removed with the old fence, and not replaced when the new fences were erected.
On a sunny day (Wed, 30 Jan 2013 22:09:45 +0000) it happened snipped-for-privacy@poppyrecords.invalid.invalid (Adrian Tuddenham) wrote in :
Yes, was wondering why 400 Hz, but was annoying in the audio.
So you get forward in furlongs / fortnight?
I'm also old enough, but not from the Isles of Fog, so the frequency is kHz (not KHz).
Ah yes, I remember them from my teenage. Have you heard any news of how Methuselah has progressed since he was at school with me? :-)
Wasn't he four years younger than you? :)
Not as far as I know.
dBmV (ref 1 millivolt) are occasionally used, as are dBKTB.
50 ohm signal sources of whatever frequency are usually calibrated terminated, whether or not they offer voltage, dBm, or both. Some ancient signal generators were calibrated "EMF into 50 (sometimes 75) ohms", which was downright confusing.A useful thing to remember is that thermal noise power in a 1Hz bandwidth, at 290K, is -174dBm, irrespective of impedance.
As I understand it, the London subway system uses two live rails, one positive, one negative, asymmetrically centered to ground. Something to do with electrolytic effects in buried metalwork.
I thought that one of the conductor rails was grounded at the sub-station but not at any other point along its length. That prevented any return currents from flowing through the earth.
Tramways are more difficult to deal with because their return conductors are the running rails and are buried in the street. Recent solutions have included polyurethane-insulated rails and earthng mats a short distance below the surface to drain away the current to a separate conductor sytem. Older systems used a negative booster, controlled by the traction current, to feed an equal but opposite current into the return rail at some remote point (to minimise the voltage difference along the rail).
Taunton had the most unusual answer to electrolytic corrosion, they effectivley used low frequency A.C. by reversing the polarity of the system each day. It didn't matter to the tram motors whether the overhead wire was positive or negative.
There is something very strange here, i learned 0 dBm as 1 mW in 600 ohms. Of course, that was about 50 years ago, they might have changed it. I also learned sometime not long after, that dBu (the "u" is really a Greek mu) is 1 uV in 50 ohms.
?-)
terminated
power
ancient
which
bandwidth,
Actually dB and for that matter bels is about power and power ratios, always irrespective of impedance.
?-)
There hasn't been any change in the definition although there has been a lot of argument about it based on misunderstanding. At least one textbook incorrectly defines decibels in terms of voltage and doesn't mention power (I hope the author corrects this in folowing editions).
Perhaps the 'u' in the 600-ohm voltage useage really is an English 'u', so as to distinguish it from the 'mu' in the 50-ohm useage?
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