Antenna question

[Bill Bowden]

On Jan 21, 2:59 pm, "Phil Allison" <phi...@tpg.com.au> wrote:

"Pawihte"



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),

** Sorry  -  but that ( erroneous) formula gives a POWER ratio.

always with a 'v' added, that I wanted to be sure.

** When another letter is added to  "dB" it changes the meaning.

Normally, dBs are pure ratios -  but if a "m" or "v" or "V" or "W" suffix is
added -  it becomes an actual level and no longer a ratio.

You need to find out what each suffix stands for and then use the number to
compute the actual quantity.

Eg.  "m" = milliwatt  -   so 6dBm equals 4 milliwatts.

....  Phil

But isn't an antenna gain said to be so many dBs, and assumed to be a
voltage ratio? If there is no load on the antenna, high impedance
input, why would power gain mean anything?

I hear AM radios need about 120 dB gain, and assume the meaning is
with a 1 microvolt input, the audio output is about 1 volt, or 120dB
higher.

-Bill

 

[whit3rd]

On Jan 21, 5:05 pm, "Phil Allison" <phi...@tpg.com.au> wrote:

[about the THAT 2181 data sheet]

** The data sheet makes it clear the gain ( and other figures) figures
refer
to a given test circuit ( figure 2) that is clearly a voltage amplifier..

Define 'clear'.  The figure 2 circuit is 'typical application circuit'
on my copy of the datasheet, NOT 'test circuit'.  There's a test circuit
mention in one footnote, on the 'electrical characteristics' data, but
nothing
similar in the discussion or on subsequent data and graphs.

** FFS dickwad  -

 the " Electrical Characteristics " table has a suffix " 2 " after the
words.

Exactly, that's the footnote.

Means ALL  the data in the table relates to that circuit.

"ALL" being six gain specifications. The rest of the datasheet,
six pages with plots of gain in dB, with discussion tidbits like
'Figure 6 shows the decibel current gain' is pretty clearly NOT
consistent with the it's-a-voltage-gain picture.

Piss off  -   you bullshitting, bloody MORON  !!!

Thanks, Phil; I see it bothers you, too.

 

[Pawihte]

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?

 

[Phil Allison]

"Pawihte"
<

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?

** This is like teaching a pig to sing ...

Oink, oink ....



..... Phil

 

[Rich Grise]

Pawihte 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?

Since you're not getting any answers, it sounds like nobody really
knows[1]. If they're selling you an antenna, they probably use voltage
gain, which would be "marketing dB," much like marketing watts output.

As long as you're consistent throughout, it probably doesn't matter
that much anyway.

Hope This Helps!
Rich
[1] I had a boss once who was looking at some HTML, and wanted me
to explain it to him. He pointed to an <a href=... tag, and said,
"what does this mean?" I looked him in the eye, and said, serious
as a heart attack, "Nobody knows."

He laughed a very healthy belly laugh, the ice was broken, and a
good time was had by all. ;-)

 

[Michael A. Terrell]

Phil Allison wrote:

"Pawihte"

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?

** This is like teaching a pig to sing ...

Oink, oink ....

Get the money back to your teacher.


--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

 

[krw@att.bizzzzzzzzzzzz]

On Sat, 22 Jan 2011 23:12:42 +1100, "Phil Allison" <phil_a@tpg.com.au> wrote:

"Pawihte"

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?


** This is like teaching a pig to sing ...

Oink, oink ....

Thanks for the lessons, Phyllis. It's always good to learn from the master.

 

[Michael A. Terrell]

Pawihte 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?

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.


--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

 

[Michael A. Terrell]

"krw@att.bizzzzzzzzzzzz" wrote:

On Sat, 22 Jan 2011 23:12:42 +1100, "Phil Allison" <phil_a@tpg.com.au> wrote:


"Pawihte"

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?


** This is like teaching a pig to sing ...

Oink, oink ....

Thanks for the lessons, Phyllis. It's always good to learn from the master.

Her latest record, 'Onik off, You pig!!!' is due to be relased on
Febuary first. Look for it at your local feed store.


--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

 

[krw@att.bizzzzzzzzzzzz]

On Sat, 22 Jan 2011 07:12:38 -0800 (PST), George Herold
<gherold@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?

 

[George Herold]

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.

George H.

 

[whit3rd]

On Jan 21, 7:57 pm, Bill Bowden <bper...@bowdenshobbycircuits.info>
wrote:

But isn't an antenna gain said to be so many dBs, and assumed to be a
voltage ratio? If there is no load on the antenna, high impedance
input, why would power gain mean anything?

No, and the 'voltage ratio' isn't any kind of possibility for an
antenna.
The antenna output, after all, is an electromagnetic field,
measured in watts/sq. meter, or volts/meter. Until you find some
way to specify a receiving antenna, you CANNOT extract a 'volts'
value for the output.

The gain of an antenna is a ratio of the peak power/steradian to the
total power/ (4*pi ). There was an advertisement for a surface mount
antenna, meant to solder a millimeter or two above the ground plane
of a printed wiring board. The antenna, according to its proud
marketer, 'features 3 dB of gain'. I giggled a LOT about that: if
you block half the radiation with a ground plane, ANY antenna
must have at least 3 dB of gain.

 

[John Fields]

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)


---
JF

 

[Pawihte]

George 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.

 

[Tom Biasi]

"Pawihte" wrote in message news:ihfe3s$9nc$1@news.eternal-september.org...

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.


It may me incorrect as to English grammar, the apostrophe in this example
would lead one to assume possession, but it is often used in this context to
make clear that one it not using a term called "dBs".
I, for one, fully accept this nomenclature.

OK, Back to electronics please.

 

[Phil Allison]

"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

 

[Gareth]

On 22/01/2011 09:20, Pawihte 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?


It's power. P1/P2 = 10^(dB/10)

6dB is a power gain of 4
10 dB is a power gain of 10

However, since power is proportional to voltage squared, you can get
straight to the voltage ratio with V1/V2 = = 10^(dB/20).

 

[Jamie]

Pawihte 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?


POWER.. always..

You can't use voltage gains with antennas because different impedance's
yield different voltages and you need to use a matching network to
transfer this level properly into and from your antenna and transmission
line to get the most out of it..RF transformer, balun, ect..

Isotropic antennas are the level of reference ( 0 dB/ 0dBi)

Any antenna that can move the wasted RF into the useable area's is
gain.. the amount of power over the power of a isotropic..

Jamie

 

[krw@att.bizzzzzzzzzzzz]

On Sat, 22 Jan 2011 17:41:38 -0800 (PST), George Herold
<gherold@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.

 

[George Herold]

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?)

George H.
- Hide quoted text -

- Show quoted text -