Help understanding voltage db vs power db.

[Adrian Tuddenham]

Phil Allison <pallison49@gmail.com> wrote:

Clifford Heath wrote:

Sorry, but decibels are not about any unit. Not power, not voltage.
They're only about ratios. They're just a log representation of a ratio,
which is a *pure unit-less number*.

** 100% WRONG.

The only quantities that can be legitimately expressed in dB are actual
power or directly relate to power.

A car can have 3dB more power than another but not 3dB more speed.

I never thought I would end up agreeing with you - but this time I do!

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

 

[Jasen Betts]

On 2020-04-18, Phil Allison <pallison49@gmail.com> wrote:

Clifford Heath is an Idiot wrote:

-----------------------------------

Decibels are all about POWER, there are no voltage decibels.

Sorry, but decibels are not about any unit. Not power, not voltage.
They're only about ratios. They're just a log representation of a ratio,
which is a *pure unit-less number*.

** 100% WRONG.

The only quantities that can be legitimately expressed in dB are actual power or directly relate to power.

A car can have 3dB more power than another but not 3dB more speed.

kinetic energy is 0.5mv^2

3db more Speed is about 1.41 times faster.

--
Jasen.

 

[Jasen Betts]

On 2020-04-18, Clifford Heath <no.spam@please.net> wrote:

> LOG(x), without qualification, means the *natural* log, not to base 10.

That depends on context, in some contexts sometimes ln(x) is natural
logarythm and log(x) is base 10.

--
Jasen.

 

[Jasen Betts]

On 2020-04-18, Pimpom <nobody@nowhere.com> wrote:

On 4/18/2020 11:56 AM, Dave Platt wrote:
In article <buwmG.430$yf3.275@fx25.iad>,
Clifford Heath <no.spam@please.net> wrote:

LOG(x), without qualification, means the *natural* log, not to base 10.

I assume you wouldn't rather be using those?

The usage I remember from my early days was that "log(x)" usually
meant to the base 10, and "ln(x)" was used to represent the natural
logarithm to the base e.


That's been my experience too. In the days before computers and
scientific calculators, log tables at the back of technical books
were often presented without specifying the base and were assumed
to be to the base 10.

a log table in some other base would be cumbersome to use.
base 10 logs work because ot is easy to scale the input and output of
a 1..10 table.

--
Jasen.

 

[Phil Allison]

amdx = dickhead:

----------------

The fact that I know: a 6db voltage gain is a 3db power gain.
If that is wrong set me straight.

** Setting a wanker you straight is a Hurculean task.

You did know that the "bel" in decibel = Alexander Graham Bell ?

So its dB not db.

Bet you got it mixed up with " dbx " plus every other stupid mistake possible.



..... Phil

 

On Saturday, April 18, 2020 at 4:32:01 AM UTC-4, Phil Allison wrote:

Clifford Heath is an Idiot wrote:

-----------------------------------

Decibels are all about POWER, there are no voltage decibels.

Sorry, but decibels are not about any unit. Not power, not voltage.
They're only about ratios. They're just a log representation of a ratio,
which is a *pure unit-less number*.

** 100% WRONG.

The only quantities that can be legitimately expressed in dB are actual power or directly relate to power.

Whatever field you are working decibels in ( I know mostly RF) there are reference levels. Reference levels such as dBm (0mW), dBW(1W) , or dBv ( a specified voltage [1V] across some KNOWN resistance [frequenty 50 ohms] which is still a reference power)

In this context, which is certainly my world and I think the context of the post, then dB's are being used in the electrical power context.

But it does all get back to context, which is why you need ...( there are some exceptions if just comparing two arbitrary signals)... some reference (dBm , dBW, dBV) to get the problem staked down.

A car can have 3dB more power than another but not 3dB more speed.



RF designers assume they're about power. Audio folk assume they are
A-weighted subjective measures of loudness. Etc.... but those are all
the assumptions of a specific community, and they're just convenient lies.


** The only convenient LIAR here is YOU.

Bugger off.

 

On Saturday, April 18, 2020 at 7:11:15 AM UTC-4, blo...@columbus.rr.com wrote:

On Saturday, April 18, 2020 at 4:32:01 AM UTC-4, Phil Allison wrote:
Clifford Heath is an Idiot wrote:

-----------------------------------

Decibels are all about POWER, there are no voltage decibels.

Sorry, but decibels are not about any unit. Not power, not voltage.
They're only about ratios. They're just a log representation of a ratio,
which is a *pure unit-less number*.

** 100% WRONG.

The only quantities that can be legitimately expressed in dB are actual power or directly relate to power.

Whatever field you are working decibels in ( I know mostly RF) there are reference levels. Reference levels such as dBm (0mW), dBW(1W) , or dBv ( a specified voltage [1V] across some KNOWN resistance [frequenty 50 ohms] which is still a reference power)

0dBm = 1 mW

Normally I do not correct trivial typing mistakes but this one I will correct because it may cause confusion

In this context, which is certainly my world and I think the context of the post, then dB's are being used in the electrical power context.

But it does all get back to context, which is why you need ...( there are some exceptions if just comparing two arbitrary signals)... some reference (dBm , dBW, dBV) to get the problem staked down.


A car can have 3dB more power than another but not 3dB more speed.



RF designers assume they're about power. Audio folk assume they are
A-weighted subjective measures of loudness. Etc.... but those are all
the assumptions of a specific community, and they're just convenient lies.


** The only convenient LIAR here is YOU.

Bugger off.

 

[Phil Hobbs]

On 2020-04-18 02:26, Dave Platt wrote:

In article <buwmG.430$yf3.275@fx25.iad>,
Clifford Heath <no.spam@please.net> wrote:

LOG(x), without qualification, means the *natural* log, not to base 10.

I assume you wouldn't rather be using those?

The usage I remember from my early days was that "log(x)" usually
meant to the base 10, and "ln(x)" was used to represent the natural
logarithm to the base e.

From a quick Google-search I find that this does seem to be a common
convention.

Writing log10(x) and ln(x) makes it explicit and avoids us being
confoosed.

log(x) meaning natural log is a convention used only in calculus
textbooks IME. I don't recall ever seeing it used in an engineering
context.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

blocher@columbus.rr.com wrote in
news:1e60f30e-9ce3-430c-9896-08303f83d743@googlegroups.com:

In this context, which is certainly my world and I think the
context of the post, then dB's are being used in the electrical
power context.

Nearly everything in the Ghz RF realm I worked with was all about
dBm. All attenuators, amplification calculations, losses, etc. all
used the dBm reference.

 

On Saturday, April 18, 2020 at 7:15:32 AM UTC-4, blo...@columbus.rr.com wrote:

On Saturday, April 18, 2020 at 7:11:15 AM UTC-4, blo...@columbus.rr.com wrote:
On Saturday, April 18, 2020 at 4:32:01 AM UTC-4, Phil Allison wrote:
Clifford Heath is an Idiot wrote:

-----------------------------------

Decibels are all about POWER, there are no voltage decibels.

Sorry, but decibels are not about any unit. Not power, not voltage.
They're only about ratios. They're just a log representation of a ratio,
which is a *pure unit-less number*.

** 100% WRONG.

The only quantities that can be legitimately expressed in dB are actual power or directly relate to power.

Whatever field you are working decibels in ( I know mostly RF) there are reference levels. Reference levels such as dBm (0mW), dBW(1W) , or dBv ( a

Correcting more errors.... 0dBW = 1 Watt, 0dBV = 1V across known resistance


a few more examples......

0dBm +30dB = 30dBm which equals 1000mW which equals 1W which equals 0dBW

3dBm = 0dBm +3dB = 2 mW

10dBm = 0dBm +10dB = 10 mW

26dBW = 0dBW +26dB = 400W





specified voltage [1V] across some KNOWN resistance [frequenty 50 ohms] which is still a reference power)

0dBm = 1 mW

Normally I do not correct trivial typing mistakes but this one I will correct because it may cause confusion

In this context, which is certainly my world and I think the context of the post, then dB's are being used in the electrical power context.

But it does all get back to context, which is why you need ...( there are some exceptions if just comparing two arbitrary signals)... some reference (dBm , dBW, dBV) to get the problem staked down.


A car can have 3dB more power than another but not 3dB more speed.



RF designers assume they're about power. Audio folk assume they are
A-weighted subjective measures of loudness. Etc.... but those are all
the assumptions of a specific community, and they're just convenient lies.


** The only convenient LIAR here is YOU.

Bugger off.

 

[Don Kuenz]

amdx <nojunk@knology.net> wrote:

I'm confused after using this calculator.
http://www.sengpielaudio.com/calculatorVoltagePower.htm

The first calculator labeled,
“ Find decibel voltage gain and ratio out/in by entering input and
output voltage:”
If I put 1 volt on the input line and 2 volts on the output line, the
calculator gives a 6db gain.

The second calculator labeled,
“Find decibel power gain and ratio out/in by entering before and after
power“
In order to enter power in Watts, I'll assume a 50 ohm system and
calculate power using
V^2/R=P. As above 1volt^2/50 =0.02 Watts for input power and 2^2/50=0.08
Watts for output power.
When I enter 0.02 and 0.08 into the second calculator, I get 6db power gain.

Back to the fact that I know, a 6db voltage gain is a 3db power gain.

So, what am I doing wrong that I don't get 3db for the power?

Thanks for your time, Mikek

It's my pleasure to review decibels along with you. Rohde Schwarz wrote
a helpful Application Note (AN) on the subject: "dB or not dB?
Everything you ever wanted to know about decibels but were afraid to
ask..." [1]

True or false: 30 dBm + 30 dBm = 60 dBm? Why does 1% work out
to be -40 dB one time but then 0.1 dB or 0.05 dB the next time?
These questions sometimes leave even experienced engineers
scratching their heads. Decibels are found everywhere, including
power levels, voltages, reflection coefficients, noise figures,
field strengths and more. What is a decibel and how should we
use it in our calculations? This Application Note is intended
as a refresher on the subject of decibels. [1]

Allow me to repeat the fact that you know, to wit:

The fact that I know: a 6db voltage gain is a 3db power gain.
If that is wrong set me straight.

That is correct.

The most common attenuators have values of 3 dB, 6 dB, 10 dB
and 20 dB. This corresponds to voltage ratios of 0.7, 0.5, 0.3
and 0.1 or power ratios of 0.5, 0.25, 0.1 and 0.01. [1]

Note.

[1] http://www.rohde-schwarz.com/appnote/1MA98

Thank you,

--
Don Kuenz KB7RPU
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.

 

[piglet]

On 18/04/2020 4:16 pm, Jeroen Belleman wrote:

On 2020-04-18 10:32, piglet wrote:
[...]

You doubled (added 3dB to) the voltage but because P=V^2R that
quadrupled (added 6dB to) the power.

piglet

Oh no!

Doubling the voltage quadruples the power, and that's 6dB
either way.

I never realized how much confusion there is about dBs.

Jeroen Belleman

Yes, I totally agree doubling the voltage quadruples the power and that
is a 6dB increase. 3dB is always double the power, always. I think the
language and choice of wording is what is fiendish and what trips many
people up (and you spotted my trip this time).

piglet

 

[Jeroen Belleman]

On 2020-04-18 14:58, Don Kuenz wrote:
[...]

The fact that I know: a 6db voltage gain is a 3db power gain.
If that is wrong set me straight.

That is correct.

Arggh! NO!

6dB is doubling the voltage and quadrupling the power.
3dB is sqrt(2) times the voltage and twice the power.

NEVER does 6dB equal 3dB.

Jeroen Belleman

 

[Jeroen Belleman]

On 2020-04-18 10:32, piglet wrote:

You doubled (added 3dB to) the voltage but because P=V^2R that
quadrupled (added 6dB to) the power.

piglet

Oh no!

Doubling the voltage quadruples the power, and that's 6dB
either way.

I never realized how much confusion there is about dBs.

Jeroen Belleman

 

[whit3rd]

On Saturday, April 18, 2020 at 1:32:01 AM UTC-7, Phil Allison wrote:

Clifford Heath is an Idiot wrote:

-----------------------------------

Decibels are all about POWER, there are no voltage decibels.

Sorry, but decibels are not about any unit. Not power, not voltage.
They're only about ratios. They're just a log representation of a ratio,
which is a *pure unit-less number*.

** 100% WRONG.

The only quantities that can be legitimately expressed in dB are actual power or directly relate to power.

No, not wrong. If a ratio is expressed in logarithm form, it can be given the same name
as the Bell System's old proprietary labels on their AC voltmeters 'dBm' only if the
ratio is of milliwatts (because that's what the 'm' stood for; milliwatts into the standard 600 ohm load).
But, if you care to put another third letter on, or otherwise give an explanation, the
nomenclature is entirely repurpose-able.

Language is open that way. Dictionaries have to conform to usages.

 

[Phil Hobbs]

On 2020-04-18 18:13, whit3rd wrote:

On Saturday, April 18, 2020 at 1:32:01 AM UTC-7, Phil Allison wrote:
Clifford Heath is an Idiot wrote:

-----------------------------------

Decibels are all about POWER, there are no voltage decibels.

Sorry, but decibels are not about any unit. Not power, not voltage.
They're only about ratios. They're just a log representation of a ratio,
which is a *pure unit-less number*.

** 100% WRONG.

The only quantities that can be legitimately expressed in dB are actual power or directly relate to power.

No, not wrong. If a ratio is expressed in logarithm form, it can be given the same name
as the Bell System's old proprietary labels on their AC voltmeters 'dBm' only if the
ratio is of milliwatts (because that's what the 'm' stood for; milliwatts into the standard 600 ohm load).
But, if you care to put another third letter on, or otherwise give an explanation, the
nomenclature is entirely repurpose-able.

Language is open that way. Dictionaries have to conform to usages.

The main utility of technical language is brevity. Using decibels to
refer to anything other than power ratios erodes the usefulness of the
term.

There are lots of specialized decibel units: dbA, dbC, dBm0, dBrnC0, and
so on. They're all power ratios taken under different standard
measuring conditions.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Phil Hobbs]

On 2020-04-18 04:48, Jasen Betts wrote:

On 2020-04-18, Phil Allison <pallison49@gmail.com> wrote:
Clifford Heath is an Idiot wrote:

-----------------------------------

Decibels are all about POWER, there are no voltage decibels.

Sorry, but decibels are not about any unit. Not power, not voltage.
They're only about ratios. They're just a log representation of a ratio,
which is a *pure unit-less number*.

** 100% WRONG.

The only quantities that can be legitimately expressed in dB are actual power or directly relate to power.

A car can have 3dB more power than another but not 3dB more speed.

kinetic energy is 0.5mv^2

3db more Speed is about 1.41 times faster.

Neither one is power.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Ricky C]

On Saturday, April 18, 2020 at 6:13:21 PM UTC-4, whit3rd wrote:

On Saturday, April 18, 2020 at 1:32:01 AM UTC-7, Phil Allison wrote:
Clifford Heath is an Idiot wrote:

-----------------------------------

Decibels are all about POWER, there are no voltage decibels.

Sorry, but decibels are not about any unit. Not power, not voltage.
They're only about ratios. They're just a log representation of a ratio,
which is a *pure unit-less number*.

** 100% WRONG.

The only quantities that can be legitimately expressed in dB are actual power or directly relate to power.

No, not wrong. If a ratio is expressed in logarithm form, it can be given the same name
as the Bell System's old proprietary labels on their AC voltmeters 'dBm' only if the
ratio is of milliwatts (because that's what the 'm' stood for; milliwatts into the standard 600 ohm load).
But, if you care to put another third letter on, or otherwise give an explanation, the
nomenclature is entirely repurpose-able.

Language is open that way. Dictionaries have to conform to usages.

You are not disagreeing with Phil. He said dB numbers relate to power. You said the Bell System's voltmeters were labeled in dBm because that was related to a mW reference power. You are supporting his point.

Is there such a thing as dBg - dB grams? No.

--

Rick C.

++ Get 1,000 miles of free Supercharging
++ Tesla referral code - https://ts.la/richard11209

 

[Phil Allison]

whit3rd needs to FUCK OFF

------------------------

** 100% WRONG.

The only quantities that can be legitimately expressed in dB are
actual power or directly relate to power.

No, not wrong.

** Listen you ridiculous fuckhead - we have all long known you are a fucking nut case.

Honestly, YOU do not need to KEEP on proving it !!!


..... phil

 

Phil Allison <pallison49@gmail.com> wrote in
news:45690ac4-246f-413a-8027-28b92d05043e@googlegroups.com:

whit3rd needs to FUCK OFF

------------------------

After careful consideration, I have come to the conclusion that you
pull this shit and nobody filters you and they respond to you. I call
one guy an asshole and the entire group filters me. You guys are
*special*.