Reply by Tauno Voipio●September 23, 20152015-09-23
On 23.9.15 17:34, b2508 wrote:
>> On Tue, 15 Sep 2015 08:06:22 -0500, b2508 wrote:
>
>> Or, to get even more distressingly physical, because in a REAL radio you
>
>> can't have IMAGINARY numbers running around? So the circuit designers
>> are constrained -- yes, constrained!, tied down!, chained, even! -- to
>> either having a single LO signal or trying to simulate a complex signal
>> by making a pair of them that are very accurately 90 degrees apart (which
>
>> isn't at all trivial, even in an IC)?
>
>> Tim Wescott
>> Wescott Design Services
>> http://www.wescottdesign.com
>
> Why would they try to simulate complex signal out of real one? What is the
> benefit of this? Is there anywhere a very good article explaining the
> reasons to use IQ data at all? I don't get it anymore, are they complex,
> are they used for easier modulation process, are they fake, what are they?
>
> ---------------------------------------
> Posted through http://www.DSPRelated.com
Google for 'image rejection mixer'.
--
-TV
Reply by b2508●September 23, 20152015-09-23
>On Tue, 15 Sep 2015 08:06:22 -0500, b2508 wrote:
>Or, to get even more distressingly physical, because in a REAL radio you
>can't have IMAGINARY numbers running around? So the circuit designers
>are constrained -- yes, constrained!, tied down!, chained, even! -- to
>either having a single LO signal or trying to simulate a complex signal
>by making a pair of them that are very accurately 90 degrees apart (which
Why would they try to simulate complex signal out of real one? What is the
benefit of this? Is there anywhere a very good article explaining the
reasons to use IQ data at all? I don't get it anymore, are they complex,
are they used for easier modulation process, are they fake, what are they?
---------------------------------------
Posted through http://www.DSPRelated.com
Reply by robert bristow-johnson●September 17, 20152015-09-17
On 9/16/15 9:02 AM, makolber@yahoo.com wrote:
>
>>>
>>> If the signal is real it only takes one cable to transport.
>>> If the signal is quadrature it must have two cables to transport.
>>>
>
> it is also more clear if you use an alternate terminology..
>
> real = single dimensional
>
> complex = two dimensional
>
> imaginary = the second dimension of the two dimensional values.
>
problem is that this terminology is not always correct.
C != R^2
two-vectors are not the same as complex numbers. they have different
operations (and rules) regarding each.
--
r b-j rbj@audioimagination.com
"Imagination is more important than knowledge."
Reply by ●September 16, 20152015-09-16
> >
> > If the signal is real it only takes one cable to transport.
> > If the signal is quadrature it must have two cables to transport.
> >
it is also more clear if you use an alternate terminology..
real = single dimensional
complex = two dimensional
imaginary = the second dimension of the two dimensional values.
Mark
Reply by ●September 16, 20152015-09-16
On Tuesday, September 15, 2015 at 1:09:26 PM UTC-4, Tim Wescott wrote:
> On Tue, 15 Sep 2015 07:21:05 -0700, makolber wrote:
>
> > On Tuesday, September 15, 2015 at 9:35:36 AM UTC-4, Tauno Voipio wrote:
> >> On 15.9.15 16:06, b2508 wrote:
> >> > Well, probably sounds stupid but I get quite confused on this. In my
> >> > specification I get Intermediate Frequency data as real from third
> >> > party RF Front end.
> >> >
> >> > Isn't RF Data suppose to be real? Then I assume it was mixed with
> >> > some LO to downconvert it from RF to IF. How this this result in a
> >> > real signal?
> >>
Then there are no negative numbers too?
Imaginary numbers is how God draws circles.
> >>
> >> You may have either, depending on the mixer. If nothing is said, it is
> >> pretty safe to assume that IF is a real, band-limited signal.
> >>
> >> If the mixer has two channels with local oscillators at 90 degree phase
> >> difference, you can have complex IF signal pair at the output.
> >>
> >> --
> >>
> >> -TV
> >
> > as a simple minded hardware guy... my rule is
> >
> > if the signal takes one cable to transport, it is real..
> > if the signal takes two cables to transport i.e I and Q. , it is
> > complex,
> >
> > not sure if this is technically correct.
>
> It's not an IIF proposition. You can turn it around:
>
> If the signal is real it only takes one cable to transport.
> If the signal is quadrature it must have two cables to transport.
>
> But there are other ways you can put a group of related signals onto
> multiple cables that aren't I and Q.
>
> Being a stickler about this, I wouldn't even say "I and Q is complex" --
> I would say "I and Q is _pretending_ to be complex". Because -- there
> ain't no imaginary numbers in this real world of ours.
>
> --
>
> Tim Wescott
> Wescott Design Services
> http://www.wescottdesign.com
Reply by Les Cargill●September 15, 20152015-09-15
Tim Wescott wrote:
> On Tue, 15 Sep 2015 07:21:05 -0700, makolber wrote:
>
>> On Tuesday, September 15, 2015 at 9:35:36 AM UTC-4, Tauno Voipio wrote:
>>> On 15.9.15 16:06, b2508 wrote:
>>>> Well, probably sounds stupid but I get quite confused on this. In my
>>>> specification I get Intermediate Frequency data as real from third
>>>> party RF Front end.
>>>>
>>>> Isn't RF Data suppose to be real? Then I assume it was mixed with
>>>> some LO to downconvert it from RF to IF. How this this result in a
>>>> real signal?
>>>
>>>
>>> You may have either, depending on the mixer. If nothing is said, it is
>>> pretty safe to assume that IF is a real, band-limited signal.
>>>
>>> If the mixer has two channels with local oscillators at 90 degree phase
>>> difference, you can have complex IF signal pair at the output.
>>>
>>> --
>>>
>>> -TV
>>
>> as a simple minded hardware guy... my rule is
>>
>> if the signal takes one cable to transport, it is real..
>> if the signal takes two cables to transport i.e I and Q. , it is
>> complex,
>>
>> not sure if this is technically correct.
>
> It's not an IIF proposition. You can turn it around:
>
> If the signal is real it only takes one cable to transport.
> If the signal is quadrature it must have two cables to transport.
>
> But there are other ways you can put a group of related signals onto
> multiple cables that aren't I and Q.
>
> Being a stickler about this, I wouldn't even say "I and Q is complex" --
> I would say "I and Q is _pretending_ to be complex". Because -- there
> ain't no imaginary numbers in this real world of ours.
>
Two wrongs don't make a right, but two reals might make an imaginary.
--
Les Cargill
Reply by glen herrmannsfeldt●September 15, 20152015-09-15
Tim Wescott <seemywebsite@myfooter.really> wrote:
> On Tue, 15 Sep 2015 07:21:05 -0700, makolber wrote:
(snip)
>> as a simple minded hardware guy... my rule is
>> if the signal takes one cable to transport, it is real..
>> if the signal takes two cables to transport i.e I and Q. , it is
>> complex,
>> not sure if this is technically correct.
> It's not an IIF proposition. You can turn it around:
> If the signal is real it only takes one cable to transport.
> If the signal is quadrature it must have two cables to transport.
> But there are other ways you can put a group of related signals onto
> multiple cables that aren't I and Q.
> Being a stickler about this, I wouldn't even say "I and Q is complex" --
> I would say "I and Q is _pretending_ to be complex". Because -- there
> ain't no imaginary numbers in this real world of ours.
I suppose, but in an analog system, the signal in the cable is
analogous to some physicial quantity, not the actual quantity,
so it doesn't seem so hard to call it imaginary.
Also, there are some physical quantities that really are complex,
such as index of refraction:
https://en.wikipedia.org/wiki/Refractive_index#Complex_refractive_index
The index of refraction depends on the motion of electrons in a
material subject to an electromagnetic field. They don't know that
one motion contributes to changing the phase velocity, and another
to absorption.
If that isn't obvious enough, consider that the index of refraction
is the complex square root of the dielectric constant. (That is,
relative pemittivity.)
https://en.wikipedia.org/wiki/Refractive_index#Relative_permittivity_and_permeability
Again, the electrons don't know the difference, but note also how
the square root mixes the real and imaginary parts.
Phasors, on the other hand, are an artificial use of complex math
to measure quantities that are basically real, but might have
different phases.
-- glen
Reply by robert bristow-johnson●September 15, 20152015-09-15
On 9/15/15 1:09 PM, Tim Wescott wrote:
> ...
> Being a stickler about this, I wouldn't even say "I and Q is complex" --
> I would say "I and Q is _pretending_ to be complex".
agree with everything up to here...
> Because -- there ain't no imaginary numbers in this real world of ours.
i would not agree with that.
i might state it as "there ain't no imaginary physical quantities in
this real world of ours."
"number" != "physical quantity"
--
r b-j rbj@audioimagination.com
"Imagination is more important than knowledge."
Reply by Steve Pope●September 15, 20152015-09-15
<makolber@yahoo.com> wrote:
>as a simple minded hardware guy... my rule is
>if the signal takes one cable to transport, it is real..
Yep
>if the signal takes two cables to transport i.e I and Q. , it is complex,
Depends.
A signal comprised of two real-valued signals is only a "complex"
signal if has some quality about it, such that it makes sense to
view it on the complex plane.
For example, if one signal is an FM-modulated carrier, and the
second signal is a voltage level corresponding to how sunny it is in
Mexico City, that is not a complex signal.
Steve
Reply by Tim Wescott●September 15, 20152015-09-15
On Tue, 15 Sep 2015 07:21:05 -0700, makolber wrote:
> On Tuesday, September 15, 2015 at 9:35:36 AM UTC-4, Tauno Voipio wrote:
>> On 15.9.15 16:06, b2508 wrote:
>> > Well, probably sounds stupid but I get quite confused on this. In my
>> > specification I get Intermediate Frequency data as real from third
>> > party RF Front end.
>> >
>> > Isn't RF Data suppose to be real? Then I assume it was mixed with
>> > some LO to downconvert it from RF to IF. How this this result in a
>> > real signal?
>>
>>
>> You may have either, depending on the mixer. If nothing is said, it is
>> pretty safe to assume that IF is a real, band-limited signal.
>>
>> If the mixer has two channels with local oscillators at 90 degree phase
>> difference, you can have complex IF signal pair at the output.
>>
>> --
>>
>> -TV
>
> as a simple minded hardware guy... my rule is
>
> if the signal takes one cable to transport, it is real..
> if the signal takes two cables to transport i.e I and Q. , it is
> complex,
>
> not sure if this is technically correct.
It's not an IIF proposition. You can turn it around:
If the signal is real it only takes one cable to transport.
If the signal is quadrature it must have two cables to transport.
But there are other ways you can put a group of related signals onto
multiple cables that aren't I and Q.
Being a stickler about this, I wouldn't even say "I and Q is complex" --
I would say "I and Q is _pretending_ to be complex". Because -- there
ain't no imaginary numbers in this real world of ours.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com