for breakfast ! After which I'm employed to sort out their f*ck-ups.
Appears to be? Do you have a problem with *voltage* dividers? Do you have a problem calculating 20log(.5)?
Umm, isn't 1/2 voltage = 1/4 power? ...thus 6bB, either way (funny how the arithmetic works out).
LOL! You're priceless.
-- Keith
..............................................................................
The potential divider is formed by the source Z ( 600 ohms in this case ) and the load Z ( also 600 ohms ).
Nother more complicated than high school math / science should illustrate that forms a potential divider with a value of 0.5.
No-one works that way any more actually but I've been there, done that, got the diploma. Old ATRS ( analogue tape recorders ) that we used at Sound Developments for example ( toob based Ampex 350Cs and 351s ) had a selector switch that chose between
10k ( bridging ) load and 600 ohm ( terminated ) load. When on a 600 ohm circuit, select terminated and the level drops by 6dB relative to bridging assuming nothing else is on the circuit. You can even see it on their VU meters !Btw - try working out the power supplied by the signal *source*.
You may get a surprise ! And I mean *work it out* not believe what the faeries at the end of the garden say !
Graham
What does "impedance matching" or "maximum power transfer" mean to you? Hint: It's a R/R+R voltage divider.
Well, a *voltage* divider divides, um, voltage. Thus 20log(.5) or 6dB.
...and an R/R+R voltage divider does what to the power level. Another hint: It drops it by 6db. P=V^2/r sorta thing, dontcha know.
Wow, you know how to use Google. Now try learning something about electronics.
Man you are dense. If you drop the voltage to half, the power is quartered; 6db. The arithmetic works again.
You are amazing!
That's well known in these parts. Now what happens to the power when the voltage is halved (we are talking about a R/R+R voltage divider here). Is it really your position that it is cut in half?
Let me try translating into idioteese; YOU DON'T HAVE HALF THE POWER. YOU HAVE ONE QUARTER THE POWER. ONE QUARTER POWER = 6dB, AND AGAIN, THE MATH WORKS).
Amazing. Simply amazing.
-- Keith
breakfast ! After which I'm employed to sort out their f*ck-ups.
The 0.5 appears to be correct, but the -6dB he pulled out of his arse. If he had bothered to read the references I provided, or even done a basic web search, he would have found out that half the voltage equals
-6dB but half the power equals -3dB. Alas, he is ineducable and thinks that aserting "0.5 equals -6dB" over and over again does not change the reality of 0.5 equaling -3dB when measuring power.
He is also too dim to realize how silly he looks flaming away at someone who has killfiled him and thus cannot see his posts.
Do you often talk about yourself?
Nonsense! Decibels are dimensionless. Watts/watts is dimensionless, as is Volts/volts, or SPL/SPL. Decibels is simply a log-scaled ratio of two quantities. It's useful because many things in nature are log- scaled.
That is scary.
I see. You're too stupid to be educated. ...too stubborn to read.
Oh no! I've been plonked! What will I do? ...better plonk all the rest of the engineers here too.
BTW, your followup-to alt.dev.null didn't work. What a candy-assed loser!
-- Keith
Given the repeated basic errors that the poster in question has made, I was not sure whether he meant voltage when he wrote "potential" Thus my usage of "appears to be." One can't be too careful when dealing with the ineducable; sometimes they appear to make sense when actually they are simply lacking the vocabulary to express their ignorance.
Nope. Do *you* have a problem calculating 10log(.5)?
Do you have a problem with the established fact that decibels are, by definition, a ratio of *power* levels?
"bel (B): A unit of measure of ratios of power levels, i.e., relative power levels. Note 1: The number of bels for a given ratio of power levels is calculated by taking the logarithm, to the base 10, of the ratio. Mathematically, the number of bels is calculated as B = log10(P 1/P 2) where P 1 and P 2 are power levels. Note 2: The dB, equal to 0.1 B, is a more commonly used unit." Source:
If you had bothered to read the references I provided, or even done a basic web search, you would have found out that half the voltage equals
-6dB but half the power equals -3dB.
Do A Google web search on [ decibels dB power -3db half voltage -6db ] (
Key quotes from the first ten pages returned by the above search:
"The -3 dB point is often referred to as a "half-power point"
"A level difference of 3 dB is roughly double/half power"
"notice at each level the voltage or current dB value is twice the power dB value"
" Decibels Power Voltage
----------------------- 3 2 1.4 6 6 2.0 "
"the formula for dB in power is 10 times the logarithm of p1/p2 but the formula for dB in voltage is 20 times the logarithm of v1/v2."
"Look at the decibel equivalents for a power change of 2.0 and for 0.5. If you double or halve the power then this gives very close to 3 dBs. This is only coincidence, but it explains the frequent references you see to 'the -3 dB point': it really means half the power."
Half the voltage equals -6dB. Half the power equals -3dB. Double the voltage equals +6dB. Double the power equals +3dB. Anyone who disagrees with this basic fact after having the references proving it provided to him is willfully ignorant.
Obviously, some of you have never had occasion to deal with dBv (that¹s Volts), but your ignorance does not make the measurements and calculations non-existant.
According to my Bell "Green Brain," we even have dB=20 log I1/I2 (that's I as in current).
I bet when I suggested to Kevin that he put 3 dB of the total weight in each arm he even knew what I meant.
Don
A little problem with dBm; it isn't a ratio. dBm expresses a reference to
1 mW. 30 dBm= 1W.Don
I would agree if the statement was made by a "normal" person, but I have found that the ineducable can, by random chance, stumble on to the correct terminology without having any real understanding. Thus my usage of "appears to be."
Decibels are units of power, not voltage.
The children who played with Mattel's best selling new toy for the year 2000 and the pilots who fly airlanes tested with my AV-8B Harrier actuator test system seem to be satisfied with my abilities.
I deleted the rest of whatever you had to say unread. My time is too valuable to waste on someone who thinks that personal attacks are a substitute for a civil discussion of the topic at hand.
*plonk*
I agree 100%. I was trying to accomodate the existing sloppy thinking of certain ignorant induhviduals, but I see now that doing so was a mistake; they just run in cyircles shouting "0.5 is -6dB!
0.5 is -6dB!" and flaming anyone who tries to educate them.Thank you for the excellent advice.
Wrong. Decibels are an expression of the RATIO of two powers, OR two voltages, and, in most applications, the method being used (power or voltage ratios) is usually specified, except in some audiophool crap as marketing hype. "Peak Envelope Power", indeed.
Oh, go plonk your own self.
Good Luck! Rich [aside - while seeking out Guy's personal NG to crosspost this to - he had followups set to alt.null, as per usual - I found out that there isn't any such thing. It's dead already. Apparently, he couldn't find enough people on Planet Earth to support a Guy Macon USENET blog. Oh, well.]
way
to
and
to
It's a ratio to 1 milliwatt.
Precisely.
But he's promised to change:
But we each need to let go of the unlovingness within ourselves, to really heal.
-- Rich for further information, please visit http://www.godchannel.com
That is the formula for calculating decibels, decibels are defined with respect to power.
[...]There is no such thing as a 'voltage decibel' so please avoid using the expression, it can only lead to confusion and sloppy thinking.
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
I think his point was that he wanted to say something that was right.
A 'dB' is a certain ratio of powers. A 'dBm' is an expression of the ratio of the expressed power to a milliwatt, therefore, it is a dimension, if you will. It's a number of milliwatts, expressed in a log scale. A dBV, like he said, is the ratio of the applied voltage to one volt, expressed as a log, but because watts are proportional to volts squared, dB Volts are 20 log, and dB milliwatts are 10 log.
Hope This Helps! Rich
Guy Macon, you're being a twit.
0.5 x Volts _IS_ -6dB Power, because power is proportional to the square of the voltage. Remember, P = E^2 / R ?Please go re-take high school logarithms and algebra. And maybe Ohm's Law, or whatever that next one is, P = E * I.
Thanks, Rich
-6dB was and is the correct answer, you were, are and continue to be plain wrong. Read it and weep, sorry.
--
Thanks,
- Win
What's with the "yes's?" I didn't ask if I was correct.
My point is, dB expresses a ratio, for example, of two powers. A 10dB increase in power my be from 0.1 Watt, to 10 Watts; or 10 Watts to 100 Watts. It conveys no absolute info without being given a reference.
0 dBm is a specific amplitude.BIG difference.
...
Decibels are, as you say, dimensionless; but they are specifically a way of expressing the ratio of two power levels - only power levels, not voltages or currents or anything else.
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
No no no no *NO* ! dBs are simply ratios. They can however be referred to units such as dBV ( decibel Volt ) , dBm ( decibel miliwatt ) and so on and are *widely* used in this way throughout the electronics industry !
What the heck has got into this thread ? God Almighty !
Graham
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