G
George Herold
Guest
On Friday, April 17, 2020 at 9:41:42 AM UTC-4, amdx wrote:
Yes, 20*log(V1/V2), if you must.
GH
Yes, 20*log(V1/V2), if you must.
GH
R
Ricky C
Guest
On Friday, April 17, 2020 at 1:08:03 PM UTC-4, George Herold wrote:
Yeah, but then you'd be talking about 0.301 dB and 0.602 dB and we'd still have people confused about doubling power vs. doubling voltage. What's really different except we are working with 10 times smaller numbers?
When they teach Bells, they should ignore the deci part to get the idea across, then say, "For convenience we commonly use dB in the same way we use dl or cm".
Actually, I don't know of any common usage of the deci prefix other than dB and dl. Even dl is only used in medicine where it is commonly mixed with units like ug/dl for some bizarre reason. The medical community is nuts when it comes to units. But they are great at saving our asses!
--
Rick C.
-- Get 1,000 miles of free Supercharging
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On Friday, April 17, 2020 at 8:36:47 AM UTC-4, pcdh...@gmail.com wrote:
The fact that I know: a 6db voltage gain is a 3db power gain.
If that is wrong set me straight.
As the wise man said, "It ain't what you don't know that hurts you--it's what you do know that ain't so."
Decibels are a convenient means for expressing *power ratios*. Keep that in mind and your troubles will disappear. (These ones, anyway.)
dB = 10 log(P1/P2),
where P1 and P2 are in units of power.
Just as an aside, I find the factor of ten (10) to be 'an issue'*
in my brain. I'd much rather have a straight LOG(P1/P2).
Yeah, but then you'd be talking about 0.301 dB and 0.602 dB and we'd still have people confused about doubling power vs. doubling voltage. What's really different except we are working with 10 times smaller numbers?
When they teach Bells, they should ignore the deci part to get the idea across, then say, "For convenience we commonly use dB in the same way we use dl or cm".
Actually, I don't know of any common usage of the deci prefix other than dB and dl. Even dl is only used in medicine where it is commonly mixed with units like ug/dl for some bizarre reason. The medical community is nuts when it comes to units. But they are great at saving our asses!
--
Rick C.
-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209
J
Jeroen Belleman
Guest
On 2020-04-17 19:32, Ricky C wrote:
There seems to be a propensity of many branches of science and
technology to choose their units such that the most common
values end up in the interval 1..100. Never mind that a weird
unit is harder to grasp than a very big or very small value.
Cosmologists are real artists in that respect. For example,
Hubble's constant is really just the inverse of the age of the
universe, but who'd notice?
Jeroen --stamp out convenience units-- Belleman
On Friday, April 17, 2020 at 1:08:03 PM UTC-4, George Herold wrote:
On Friday, April 17, 2020 at 8:36:47 AM UTC-4, pcdh...@gmail.com
wrote:
The fact that I know: a 6db voltage gain is a 3db power gain.
If that is wrong set me straight.
As the wise man said, "It ain't what you don't know that hurts
you--it's what you do know that ain't so."
Decibels are a convenient means for expressing *power ratios*.
Keep that in mind and your troubles will disappear. (These ones,
anyway.)
dB = 10 log(P1/P2),
where P1 and P2 are in units of power.
Just as an aside, I find the factor of ten (10) to be 'an issue'*
in my brain. I'd much rather have a straight LOG(P1/P2).
Yeah, but then you'd be talking about 0.301 dB and 0.602 dB and we'd
still have people confused about doubling power vs. doubling voltage.
What's really different except we are working with 10 times smaller
numbers?
When they teach Bells, they should ignore the deci part to get the
idea across, then say, "For convenience we commonly use dB in the
same way we use dl or cm".
Actually, I don't know of any common usage of the deci prefix other
than dB and dl. Even dl is only used in medicine where it is
commonly mixed with units like ug/dl for some bizarre reason. The
medical community is nuts when it comes to units. But they are great
at saving our asses!
There seems to be a propensity of many branches of science and
technology to choose their units such that the most common
values end up in the interval 1..100. Never mind that a weird
unit is harder to grasp than a very big or very small value.
Cosmologists are real artists in that respect. For example,
Hubble's constant is really just the inverse of the age of the
universe, but who'd notice?
Jeroen --stamp out convenience units-- Belleman
R
Ricky C
Guest
On Friday, April 17, 2020 at 2:01:46 PM UTC-4, Pimpom wrote:
Yeah, but who uses the (small) calorie? I've never run into a use of it.
I like the definition of calorie...
cal¡o¡rie
/Ëkal(É)rÄ/
noun
noun: small calorie; plural noun: small calories; noun: large calorie; plural noun: large calories; noun: Cal
1. the energy needed to raise the temperature of 1 gram of water through 1 °C (now usually defined as 4.1868 joules).
2. the energy needed to raise the temperature of 1 kilogram of water through 1 °C, equal to one thousand small calories and often used to measure the energy value of foods.
Two completely different definitions casually placed side by side as if there is no contradiction at all.
It's a bastard unit and all use of either version should be outlawed on penalty of eating Twinkies.
The amazing thing is every day I eat enough energy to raise the temperature of a kg of water by 2000 degrees C! What do I do with all that energy???
--
Rick C.
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Yeah, but who uses the (small) calorie? I've never run into a use of it.
I like the definition of calorie...
cal¡o¡rie
/Ëkal(É)rÄ/
noun
noun: small calorie; plural noun: small calories; noun: large calorie; plural noun: large calories; noun: Cal
1. the energy needed to raise the temperature of 1 gram of water through 1 °C (now usually defined as 4.1868 joules).
2. the energy needed to raise the temperature of 1 kilogram of water through 1 °C, equal to one thousand small calories and often used to measure the energy value of foods.
Two completely different definitions casually placed side by side as if there is no contradiction at all.
It's a bastard unit and all use of either version should be outlawed on penalty of eating Twinkies.
The amazing thing is every day I eat enough energy to raise the temperature of a kg of water by 2000 degrees C! What do I do with all that energy???
--
Rick C.
-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209
P
Pimpom
Guest
On 4/17/2020 11:02 PM, Ricky C wrote:
And they mess up the calorie unit, speaking of 1000 calories by
names like 'food calorie', 'large calorie' or 'kilogram calorie'
which are often shortened to just 'calorie'.
I like to tease my doctor friends with something like "Look, we
have to deal with hundreds of different products all the time
while you doctors have been dealing with a model that's remained
unchanged for thousands of years. Yet you still know only a
fraction of what there is to know about it."
One doctor came back with "You can turn machines off." To which I
replied "Yeah, and you have anesthetics".
And they mess up the calorie unit, speaking of 1000 calories by
names like 'food calorie', 'large calorie' or 'kilogram calorie'
which are often shortened to just 'calorie'.
I like to tease my doctor friends with something like "Look, we
have to deal with hundreds of different products all the time
while you doctors have been dealing with a model that's remained
unchanged for thousands of years. Yet you still know only a
fraction of what there is to know about it."
One doctor came back with "You can turn machines off." To which I
replied "Yeah, and you have anesthetics".
P
Pimpom
Guest
On 4/17/2020 11:43 PM, Ricky C wrote:
I do, for one, albeit rarely. We still used cgs units when I was
in college.
......<snip>.......
I was idly chatting with two doctors on my porch last year when
the talk turned to the discomfort of sitting in a
non-airconditioned car in the summer. I did a quick mental
calculation and pronounced that, based on the energy value of the
food we eat, two adult humans sitting in a car generate enough
heat to boil one liter of water every half-hour. They were astounded.
I do, for one, albeit rarely. We still used cgs units when I was
in college.
......<snip>.......
I was idly chatting with two doctors on my porch last year when
the talk turned to the discomfort of sitting in a
non-airconditioned car in the summer. I did a quick mental
calculation and pronounced that, based on the energy value of the
food we eat, two adult humans sitting in a car generate enough
heat to boil one liter of water every half-hour. They were astounded.
P
Phil Hobbs
Guest
On 2020-04-17 15:04, Pimpom wrote:
I do electromagnetic calculations in Gaussian units (rationalized cgs
ESU). It gets rid of all the mu-noughts and epsilon-noughts, which
saves blunders. Converting to SI at the end is trivial.
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
I do electromagnetic calculations in Gaussian units (rationalized cgs
ESU). It gets rid of all the mu-noughts and epsilon-noughts, which
saves blunders. Converting to SI at the end is trivial.
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
G
George Herold
Guest
On Friday, April 17, 2020 at 2:16:53 PM UTC-4, Jeroen Belleman wrote:
Yeah, (Well fixing everyone's temperature scale to
absolute zero.. is more 'important' than some power ratio.
if that was the 1-100 reference?.)
Exponentially speaking, I think my brain starts to
shut down around 10^10...
10^20 is almost meaningless.
(yeah no real good feel for a mole of atoms.)
George H.
On 2020-04-17 19:32, Ricky C wrote:
On Friday, April 17, 2020 at 1:08:03 PM UTC-4, George Herold wrote:
On Friday, April 17, 2020 at 8:36:47 AM UTC-4, pcdh...@gmail.com
wrote:
The fact that I know: a 6db voltage gain is a 3db power gain.
If that is wrong set me straight.
As the wise man said, "It ain't what you don't know that hurts
you--it's what you do know that ain't so."
Decibels are a convenient means for expressing *power ratios*.
Keep that in mind and your troubles will disappear. (These ones,
anyway.)
dB = 10 log(P1/P2),
where P1 and P2 are in units of power.
Just as an aside, I find the factor of ten (10) to be 'an issue'*
in my brain. I'd much rather have a straight LOG(P1/P2).
Yeah, but then you'd be talking about 0.301 dB and 0.602 dB and we'd
still have people confused about doubling power vs. doubling voltage.
What's really different except we are working with 10 times smaller
numbers?
When they teach Bells, they should ignore the deci part to get the
idea across, then say, "For convenience we commonly use dB in the
same way we use dl or cm".
Actually, I don't know of any common usage of the deci prefix other
than dB and dl. Even dl is only used in medicine where it is
commonly mixed with units like ug/dl for some bizarre reason. The
medical community is nuts when it comes to units. But they are great
at saving our asses!
There seems to be a propensity of many branches of science and
technology to choose their units such that the most common
values end up in the interval 1..100. Never mind that a weird
unit is harder to grasp than a very big or very small value.
Cosmologists are real artists in that respect. For example,
Hubble's constant is really just the inverse of the age of the
universe, but who'd notice?
Jeroen --stamp out convenience units-- Belleman
Yeah, (Well fixing everyone's temperature scale to
absolute zero.. is more 'important' than some power ratio.
if that was the 1-100 reference?.)
Exponentially speaking, I think my brain starts to
shut down around 10^10...
10^20 is almost meaningless.
(yeah no real good feel for a mole of atoms.)
George H.
C
Cursitor Doom
Guest
On Sat, 18 Apr 2020 00:34:25 +0530, Pimpom wrote:
By how much would that half-hour be reduced if the occupants were each
given a chicken phall to eat before the experiment commenced? :-D
By how much would that half-hour be reduced if the occupants were each
given a chicken phall to eat before the experiment commenced? :-D
P
Phil Allison
Guest
blo...@columbus.rr.com wrote:
--------------------------
** Most folk connect dBs with sound - ie " dB SPL".
The reference here is a defined ( tiny) change in air pressure, so clearly not power.
But the situation is analogous to using a defined voltage as a reference and letting the actual power take care of itself.
BTW The quantity "Sound Power Level" exists too and takes account the energy in the entire sound field. While not related to the SPL at a point, for a long time the same acronym was used for both causing great confusion.
An air conditioner might carry a "65dB SPL" rating which had nothing to do with the emitted sound level or any noise standard.
..... Phil
--------------------------
** Most folk connect dBs with sound - ie " dB SPL".
The reference here is a defined ( tiny) change in air pressure, so clearly not power.
But the situation is analogous to using a defined voltage as a reference and letting the actual power take care of itself.
BTW The quantity "Sound Power Level" exists too and takes account the energy in the entire sound field. While not related to the SPL at a point, for a long time the same acronym was used for both causing great confusion.
An air conditioner might carry a "65dB SPL" rating which had nothing to do with the emitted sound level or any noise standard.
..... Phil
C
Clifford Heath
Guest
On 18/4/20 2:44 am, Adrian Tuddenham 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*.
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.
Because dB are not *about* any of those units.
Clifford Heath
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*.
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.
Because dB are not *about* any of those units.
Clifford Heath
C
Clifford Heath
Guest
On 18/4/20 3:07 am, George Herold wrote:
LOG(x), without qualification, means the *natural* log, not to base 10.
I assume you wouldn't rather be using those?
Clifford Heath
On Friday, April 17, 2020 at 8:36:47 AM UTC-4, pcdh...@gmail.com wrote:
The fact that I know: a 6db voltage gain is a 3db power gain.
If that is wrong set me straight.
As the wise man said, "It ain't what you don't know that hurts you--it's what you do know that ain't so."
Decibels are a convenient means for expressing *power ratios*. Keep that in mind and your troubles will disappear. (These ones, anyway.)
dB = 10 log(P1/P2),
where P1 and P2 are in units of power.
Just as an aside, I find the factor of ten (10) to be 'an issue'*
in my brain. I'd much rather have a straight LOG(P1/P2).
LOG(x), without qualification, means the *natural* log, not to base 10.
I assume you wouldn't rather be using those?
Clifford Heath
D
Dave Platt
Guest
In article <buwmG.430$yf3.275@fx25.iad>,
Clifford Heath <no.spam@please.net> wrote:
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.
Clifford Heath <no.spam@please.net> wrote:
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.
P
Pimpom
Guest
On 4/18/2020 11:56 AM, Dave Platt wrote:
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.
No argument there.
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.
No argument there.
Guest
On Fri, 17 Apr 2020 23:26:19 -0700, dplatt@coop.radagast.org (Dave
Platt) wrote:
Why not, there is also a ln(x) based ratio known as Neper
https://en.wikipedia.org/wiki/Neper
It was used e.g. in telephony.
lg(x) is often used for base 10 logarithm. Unfortunately, lg(x) is
also sometimes used for base 2 logarithm.
Platt) wrote:
Why not, there is also a ln(x) based ratio known as Neper
https://en.wikipedia.org/wiki/Neper
It was used e.g. in telephony.
lg(x) is often used for base 10 logarithm. Unfortunately, lg(x) is
also sometimes used for base 2 logarithm.
R
Ricky C
Guest
On Saturday, April 18, 2020 at 3:08:07 AM UTC-4, Dave Platt wrote:
Yup, ln(x) is 100% natural log. You could call it the un-common log!
--
Rick C.
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Yup, ln(x) is 100% natural log. You could call it the un-common log!
--
Rick C.
+- Get 1,000 miles of free Supercharging
+- Tesla referral code - https://ts.la/richard11209
P
piglet
Guest
On 17/04/2020 1:02 pm, amdx wrote:
You don't get 3dB power gain because the power went from 0.02 to 0.08 in
your example and that was a four-fold increase. Hence 6dB.
You doubled (added 3dB to) the voltage but because P=V^2R that
quadrupled (added 6dB to) the power.
piglet
You don't get 3dB power gain because the power went from 0.02 to 0.08 in
your example and that was a four-fold increase. Hence 6dB.
You doubled (added 3dB to) the voltage but because P=V^2R that
quadrupled (added 6dB to) the power.
piglet
P
Phil Allison
Guest
Clifford Heath is an Idiot wrote:
-----------------------------------
** 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.
** The only convenient LIAR here is YOU.
Bugger off.
-----------------------------------
** 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.
** The only convenient LIAR here is YOU.
Bugger off.
P
piglet
Guest
On 18/04/2020 8:56 am, upsidedown@downunder.com wrote:
only succeeded in losing most of the audience that had never heard of them.
piglet
Yes, I used Nepers in a presentation about RF range and attentuation but
only succeeded in losing most of the audience that had never heard of them.
piglet
P
Phil Allison
Guest
Jasen Betts wrote:
--------------------
** So you missed the word "legitimate" ?
Maybe because you are not.
...... Phil
--------------------
** So you missed the word "legitimate" ?
Maybe because you are not.
...... Phil