Any experience with negative impedance?

JL's three-wire system would take care of that though wouldn't it?

"John Devereux"

It a fool's idea that there IS even a question.

F****it.

.... Phil

The "u" in dBu means "unloaded". It is 0.775 volt into Hi Impedance.

And there is dBs, voltage into a short circuit.

That's the nice thing about standards; there are *so* many to choose from.

Really? I would of guest voltage into a shunted circuit.. :)

incidentally, my references, book that is, not the net, makes reference of dBs = 1 mW into 600 ohms (Japanese).

And that so called "0.775" which is actually "0.7746v" above is in reference to 0 dB = 1 mW into a 600 Ohm R = 0.7746Vrms across 600 ohm for "Automobiles"

So there you are, a completely messed up system.

oh btw, for TV 0 dB = 1 mW across a 75 ohm R = 1.333x10^8 * W

It's a wonder any one can keep things sorted out.

It has to be the aliens, all this disinformation!

Jamie

terminator on the 'out' port or

Well, add that one (loop through to load meters) to your toolkit. You have heard of kill-a-watt power use monitors?

?-)

on the 'out' port or

That isn't used with a constant impedance load. :)

Don't blame the standard; there is only one true standard where the dB is concerned. The mess-up has been caused by sloppy thinking, bad teaching (and the ignorance it perpetuates) and failure to see or explain the larger picture when taking convenient short-cuts.

There is a lot to be said for making sure the fundamentals are taught and understood before plunging into the real world of bullshit and jargon which surrounds any technical matters with sales potential.

Typical of the sort of misleading (mis)information which adds to the confusion is the UK Government's Health & Safety website which includes the following:

~~~~~~~~~~ How is noise measured? Noise is measured in decibels (dB). An 'A-weighting' sometimes written as 'dB(A)', is used to measure average noise levels, and a 'C-weighting' or 'dB(C)', to measure peak, impact or explosive noises.

~~~~~~~~~~

Greek

Care to cite your "one true standard:?

Bullshit noted.

Strawman noted.

Your point?

Sloppy thinking? It's a ratio, nothing more. The various applications have their own name. Should every measurement be converted to the old 600 Ohm telephone standard reference, just for drooling idiots? Or should people learn the proper application for the field where they work? I've worked commercial sound, telephone, radio & TV broadcast, recording studios, CATV and communications and have never had any trouble with dB.

Greek

What is that?

I will quote from an official publication which cites it, as I do not have acces to the original international agreement:

~~~~~~~~~~~~~

"Admiralty Handbook of Wireless Telegraphy" (H.M.S.O. 1938) Vol. 1 Appendix "A" Section 1.

THE DECIBEL AND THE NEPER.

1. Historical,

The "Decibel" is the 1/10th part of a "bel" (after Alexander Graham Bell, inventor of the telephone sounder), a unit in which one may express power ratios and gain or loss ratios of related quantities such as current and voltage. It originated in line telephony in 1923, when the American Telephone and Telegraph Company introduced a new unit, then called the "transmission unit"; this was to replace an older conception based on a ratio comparison between the decrease in signal strength produced by a given telephone line and that produced by a "mile of standard cable." In 1924 an international advisory committee on long distance telephony in Europe, together with the representatives of the Bell system, agreed to recommend their countries to adopt as standards

EITHER the "bel," a unit based on logarithms to the base 10, and equal to 10 of the American Company's "transmission units,"

OR the "neper" (after Napier), a unit based on Naperian logarithms to the base e.

The growth in popularity of the decibel, since 1929, has been so great that it is now almost a household word throughout all branches of Electrical Engineering and Acoustics.

1. Definitions,

THE DECIBEL:- Two powers P1 and P2 are said to differ by N "bels" when-

P1/P2 = 10^N i.e. N=Log[10] P1/P2

1. Cables Amplifiers and Attenuators

1. Voltage Gain in dBs, - In general, two powers P1 and P2 will be compared by observing either, the voltage developed across a given impedance, or, the current through it. **If the input and output impedances of (say), an amplifier are equal**, the power ratio will be proportional to the square of the voltage or current ratio.

The voltage or current ratio relation is very frequently misused to describe a power ratio without regard to the necessary conditions of equality between the input and output impedance [...examples follow...].

~~~~~~~~~~~~~

"an official publication" ROTFLOL!

No.

I presume that you are feigning ignorance because it suits your cause

-if you did not already know the significance of a publication by "H.M.S.O." you should have checked before replying.

Martin, W.H., "DeciBel --the new name for the transmission unit. Bell System Tech. J. January, 1929

Thanks. I am impaired and need constant refreshers.