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Yeah, I think it may be sometimes used just to confuse people. ItGeorge Herold wrote:
Pawihte, (listen to Phil if you want to learn something.)
dB's are a
measure of power.
I knew that. But dB is a much abused term, almost as much as
Watts in audio. Knowing or stating its correct usage is no
guarantee that it's used universally. There are many cases where
the incorrect is used as much as, if not more than, the correct
one. For example, although I'm not a native user of English, I
know that your insertion of an apostrophe in "dB's" is incorrect.
Just an illustration, no offence meant.
Sorry Phil, I didn't mean to put words in your mouth."George Herold"
Pawihte, (listen to Phil if you want to learn something.) dB's are a
measure of power.
** Phil did not say that - he did say this:
" There is only one kind of dB and it always relates to power."
Sometimes, the relationship can get a bit thin - as when a voltage ratio is
expressed in dB but the two voltage are not taken at the same point. The
context will make it clear when this is the case - egs:
Amplifier voltage gain = 60dB, CMRR = 45 dB, PSRR = 70 dB
Electronics engineers are so used to thinking about *ratios* in dBs they
contrive to use them whenever ordinary numbers get a bit awkward.
.... Phil
On Fri, 21 Jan 2011 20:54:34 -0500, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:
Jamie wrote:
Pawihte wrote:
Phil Allison wrote:
"Pawihte"
Is antenna gain in dB related to voltage or to power?
** There is only one kind of dB and it always relates to power.
3 dB is a doubling of power, 6 dB is a quadrupling of power.
In a circuit where impedance remains the same, 3dB is a 41%
increase
in voltage and 6 dB is a doubling of voltage.
Thank you. I understand the math but db or dB is so often also
used to express a voltage ratio as dBv = 20*log(V1/V2), and not
always with a 'v' added, that I wanted to be sure. Thanks again.
db normally indicates a ratio and usually is mention in the material
that you are reading, as a gain, etc.
How ever....
When not specifying a gain/ratio it's either stamped with an
additional symbol or you assume the reference to be in a particular
subject...
For example, a couple of references that would be know only by those
in the field..
TV
0 db = 1mV into a 75 ohm load
0 dBM = 1mV into a 75 ohm load.
---
"0dBM" would be referencing a megawatt as 0dB.
0dBm = 1mW into whatever impedance is specified.
0dBm = 0.224V RMS into 50 ohms, or 0.274V RMS into 75 ohms, or 0.548V
RMS into 300 ohms, or:
E = sqrt(PR)
you cuss me out like Phil did on that other thread?Power. A broadcast station is licensed for 'Effective Radiated
Power' which is the transmitter power times the antenna system's gain,
or loss in dB.
If I say, thanks for a well-reasoned answer without any profanity, will
decibels are (very nearly) always power.Which brings us back to my original question since I'm not "in
the field" of radio communication. When the gain of an antenna
design is specced as 6dB or 10dB or whatever, is that a voltage
gain or a power gain?
Again, wrong. Decibels are useful in all sorts of contexts, which isOn 2011-01-22, Pawihte <pawihte@invalid.invalid> wrote:
Which brings us back to my original question since I'm not "in
the field" of radio communication. When the gain of an antenna
design is specced as 6dB or 10dB or whatever, is that a voltage
gain or a power gain?
decibels are (very nearly) always power.
I've never used the dBV is that the log of a voltage ratio?
** No.
Fucking learn to use Google and Wiki
http://en.wikipedia.org/wiki/Decibel#Voltage
I've never used the dBV is that the log of a voltage ratio?On Sat, 22 Jan 2011 17:41:38 -0800 (PST), George Herold
gher...@teachspin.com> wrote:
On Jan 22, 11:04 am, "k...@att.bizzzzzzzzzzzz"
k...@att.bizzzzzzzzzzzz> wrote:
On Sat, 22 Jan 2011 07:12:38 -0800 (PST), George Herold
gher...@teachspin.com> wrote:
On Jan 22, 4:20 am, "Pawihte" <pawi...@invalid.invalid> wrote:
Jamie wrote:
Pawihte wrote:
Phil Allison wrote:
"Pawihte"
Is antenna gain in dB related to voltage or to power?
** There is only one kind of dB and it always relates to
power.
3 dB is a doubling of power, 6 dB is a quadrupling of power.
In a circuit where impedance remains the same, 3dB is a 41%
increase
in voltage and 6 dB is a doubling of voltage.
Thank you. I understand the math but db or dB is so often also
used to express a voltage ratio as dBv = 20*log(V1/V2), and
not
always with a 'v' added, that I wanted to be sure. Thanks
again.
db normally indicates a ratio and usually is mention in the
material
that you are reading, as a gain, etc.
How ever....
When not specifying a gain/ratio it's either stamped with an
additional symbol or you assume the reference to be in a
particular
subject...
For example, a couple of references that would be know only
by those
in the field..
Which brings us back to my original question since I'm not "in
the field" of radio communication. When the gain of an antenna
design is specced as 6dB or 10dB or whatever, is that a voltage
gain or a power gain?- Hide quoted text -
- Show quoted text -
Pawihte, (listen to Phil if you want to learn something.) dB's are a
measure of power.
Is that why an OpAmp's gain (CMRR, PSRR, ...) is expressed in dB?
I'm not sure why opamp specs are like that. (I'm always converting to
volts.)
You can always convert dB to amplitude, but dB's are the logarithim of
a power ratio, with a decimal shift.
At least that's my understanding. (Am I missing something?)
No, it's not always a power ratio or there wouldn't be units like dBV. The dB
is just as useful for calculating voltage gains (and noise, CMRR, dynamic
range...) as it is for power gains. With antennas it's always power ratios
since voltage gain is pretty meaningless, at least by itself.- Hide quoted text -
- Show quoted text -
Sorry Phil, It's just like the dBm. OK still a power ratio then. No?"George Herold is an Incorrigible Lazy Twat "
I've never used the dBV is that the log of a voltage ratio?
** No.
Fucking learn to use Google and Wiki
http://en.wikipedia.org/wiki/Decibel#Voltage
.... Phil
Yes, it's 20log(V/1V). The point being that decibels are *not* only a measureOn Jan 22, 9:25 pm, "k...@att.bizzzzzzzzzzzz"
k...@att.bizzzzzzzzzzzz> wrote:
On Sat, 22 Jan 2011 17:41:38 -0800 (PST), George Herold
gher...@teachspin.com> wrote:
On Jan 22, 11:04 am, "k...@att.bizzzzzzzzzzzz"
k...@att.bizzzzzzzzzzzz> wrote:
On Sat, 22 Jan 2011 07:12:38 -0800 (PST), George Herold
gher...@teachspin.com> wrote:
On Jan 22, 4:20 am, "Pawihte" <pawi...@invalid.invalid> wrote:
Jamie wrote:
Pawihte wrote:
Phil Allison wrote:
"Pawihte"
Is antenna gain in dB related to voltage or to power?
** There is only one kind of dB and it always relates to
power.
3 dB is a doubling of power, 6 dB is a quadrupling of power.
In a circuit where impedance remains the same, 3dB is a 41%
increase
in voltage and 6 dB is a doubling of voltage.
Thank you. I understand the math but db or dB is so often also
used to express a voltage ratio as dBv = 20*log(V1/V2), and
not
always with a 'v' added, that I wanted to be sure. Thanks
again.
db normally indicates a ratio and usually is mention in the
material
that you are reading, as a gain, etc.
How ever....
When not specifying a gain/ratio it's either stamped with an
additional symbol or you assume the reference to be in a
particular
subject...
For example, a couple of references that would be know only
by those
in the field..
Which brings us back to my original question since I'm not "in
the field" of radio communication. When the gain of an antenna
design is specced as 6dB or 10dB or whatever, is that a voltage
gain or a power gain?- Hide quoted text -
- Show quoted text -
Pawihte, (listen to Phil if you want to learn something.) dB's are a
measure of power.
Is that why an OpAmp's gain (CMRR, PSRR, ...) is expressed in dB?
I'm not sure why opamp specs are like that. (I'm always converting to
volts.)
You can always convert dB to amplitude, but dB's are the logarithim of
a power ratio, with a decimal shift.
At least that's my understanding. (Am I missing something?)
No, it's not always a power ratio or there wouldn't be units like dBV. The dB
is just as useful for calculating voltage gains (and noise, CMRR, dynamic
range...) as it is for power gains. With antennas it's always power ratios
since voltage gain is pretty meaningless, at least by itself.- Hide quoted text -
- Show quoted text -
I've never used the dBV is that the log of a voltage ratio?
I've never used the dBV is that the log of a voltage ratio?
Yes, it's 20log(V/1V).
The point being that decibels are *not* only a measure
of power (ratio).
Wow! You're sure the SMART one, Phyllis. Yes, moron, "dBV" *IS* relative tokrw@att.bizzzzzzzzzzzz
** This vile cunthead is a lying pile of dung.
I've never used the dBV is that the log of a voltage ratio?
Yes, it's 20log(V/1V).
** Which is of course indicates an actual voltage level and not a ratio.
You FUCKING MORON !!!!
You blew it, Moron. Decibels are *not* just used to measure power.The point being that decibels are *not* only a measure
of power (ratio).
** The term " dB " on its own is.
** This vile cunthead is a lying pile of dung.
I've never used the dBV is that the log of a voltage ratio?
Yes, it's 20log(V/1V).
** Which is of course indicates an actual voltage level and not a ratio.
You FUCKING MORON !!!!
Wow!
Maybe *YOU* should learn how to write, Phyllis. You really suck at it.krw@att.bizzzzzzzzzzzz
** This vile cunthead is a lying pile of dung.
I've never used the dBV is that the log of a voltage ratio?
Yes, it's 20log(V/1V).
** Which is of course indicates an actual voltage level and not a ratio.
You FUCKING MORON !!!!
Wow!
** Learn to fucking read - you ASININE LYING CUNT !!!
Dumbass, the definition is (20log10) of the voltage REFERENCED TO 1-VOLT, justdBVs indicate actual voltage levels - not a ratio.
Now Phyllis, is that any way to talk to your superiors?You FUCKWIT LYING CUNTHEAD !!
** Learn to fucking read - you ASININE LYING CUNT !!!I've never used the dBV is that the log of a voltage ratio?
Yes, it's 20log(V/1V).
** Which is of course indicates an actual voltage level and not a ratio.
You FUCKING MORON !!!!
Wow!
Dumbass,
Just to clarify: dB is relative _power_ measurement (10logP1/P2). The dBTom Biasi wrote:
"Pawihte" wrote in message
news:ihcmg2$6k6$1@news.eternal-september.org...
I'll be grateful if you could explain this:
Is antenna gain in dB related to voltage or to power? For
example, suppose there are two receiving antennas with
different
gains, but identical in frequency, impedance and terminating
load, and antenna A has a 6dB gain over antenna B. If they are
both pointed at the same transmitting source from the same
distance, what will be the ratio of the voltages they deliver
at
the load - 4:1 or 2:1?
Conversely, if the two antennas are used as radiators and
pointed
at the same receiving antenna, what will be the ratio of the
voltages they induce in the receiving antenna?
Or are they really the same db number for voltage and power? If
voltage, 6db will be in dbv or x2, resulting in x4 power for
the
same impedance, and x4 power is 6db. Does that make any sense?
Antenna gain is usually measured in dBi. The "i" is for
isotropic.
Same power in all directions.
For some examples see here:
http://radarproblems.com/chapters/ch06.dir/ch06pr.dir/c06p6.dir/c06p6.htm
Tom
Thank you. I have read about dbi and understand the concept of a
theoretical isotropic antenna. But I believe dbd, relative to an
ideal dipole, is also used. Some specs simply say db or dB. In
the same way, I often see dbv (not necessarily in connection with
antennas) for voltage ratios where dbv = 20*log(V1/V2), but not
always with the v inserted. Anyway, my question was really not
about which ideal antenna is used as a reference, but which
db/dB.
---OK, I don't want to get all 'cranky' about it. But you can move the 2
inside the log and write it as,
10log(V^2/1V^2), and that looks a bit like a power. That dBV's are
independent of the impedance is kinda weird.
George H.
Hmm OK it's independent of the impedance. That's not a great link"George Herold is an Incorrigible Lazy Twat "
I've never used the dBV is that the log of a voltage ratio?
** No.
Fucking learn to use Google and Wiki
http://en.wikipedia.org/wiki/Decibel#Voltage
Sorry Phil, It's just like the dBm. OK still a power ratio then. No?
** Noooo !!!
Fucking learn to use Google and Wiki !!!!!!!!!!!!!!!!!
.... Phil
OK, I don't want to get all 'cranky' about it. But you can move the 2On Sun, 23 Jan 2011 17:24:59 -0800 (PST), George Herold
gher...@teachspin.com> wrote:
On Jan 22, 9:25 pm, "k...@att.bizzzzzzzzzzzz"
k...@att.bizzzzzzzzzzzz> wrote:
On Sat, 22 Jan 2011 17:41:38 -0800 (PST), George Herold
gher...@teachspin.com> wrote:
On Jan 22, 11:04 am, "k...@att.bizzzzzzzzzzzz"
k...@att.bizzzzzzzzzzzz> wrote:
On Sat, 22 Jan 2011 07:12:38 -0800 (PST), George Herold
gher...@teachspin.com> wrote:
On Jan 22, 4:20 am, "Pawihte" <pawi...@invalid.invalid> wrote:
Jamie wrote:
Pawihte wrote:
Phil Allison wrote:
"Pawihte"
Is antenna gain in dB related to voltage or to power?
** There is only one kind of dB and it always relates to
power.
3 dB is a doubling of power, 6 dB is a quadrupling of power.
In a circuit where impedance remains the same, 3dB is a 41%
increase
in voltage and 6 dB is a doubling of voltage.
Thank you. I understand the math but db or dB is so often also
used to express a voltage ratio as dBv = 20*log(V1/V2), and
not
always with a 'v' added, that I wanted to be sure. Thanks
again.
db normally indicates a ratio and usually is mention in the
material
that you are reading, as a gain, etc.
How ever....
When not specifying a gain/ratio it's either stamped with an
additional symbol or you assume the reference to be in a
particular
subject...
For example, a couple of references that would be know only
by those
in the field..
Which brings us back to my original question since I'm not "in
the field" of radio communication. When the gain of an antenna
design is specced as 6dB or 10dB or whatever, is that a voltage
gain or a power gain?- Hide quoted text -
- Show quoted text -
Pawihte, (listen to Phil if you want to learn something.) dB's are a
measure of power.
Is that why an OpAmp's gain (CMRR, PSRR, ...) is expressed in dB?
I'm not sure why opamp specs are like that. (I'm always converting to
volts.)
You can always convert dB to amplitude, but dB's are the logarithim of
a power ratio, with a decimal shift.
At least that's my understanding. (Am I missing something?)
No, it's not always a power ratio or there wouldn't be units like dBV. The dB
is just as useful for calculating voltage gains (and noise, CMRR, dynamic
range...) as it is for power gains. With antennas it's always power ratios
since voltage gain is pretty meaningless, at least by itself.- Hide quoted text -
- Show quoted text -
I've never used the dBV is that the log of a voltage ratio?
Yes, it's 20log(V/1V). The point being that decibels are *not* only a measure
of power (ratio). "dB" is unitless.- Hide quoted text -
- Show quoted text -