Analog Communication query

[Hollenburg]

Hi,
Recently in an interview one of my friend was asked some
questions.....
(1) If Digital Communication has so many advantages over Analog
communication then why do we use Analog Communication. My friend
answered simplicity to implement but they were looking for some more
specific answers.
(2) Physical realization of Phase Modulation.
(3) Can a DC source be used as a supply to PC. [As far as I know.....a
UPS does convert it to DC from the AC mains]

Can anybody plzz give me the answer of these two
questions...........Thanx.....Diba

 

[Rich Grise]

on Monday 05 July 2004 01:34 am, Hollenburg wrote:

Hi,
Recently in an interview one of my friend was asked some
questions.....
(1) If Digital Communication has so many advantages over Analog
communication then why do we use Analog Communication. My friend
answered simplicity to implement but they were looking for some more
specific answers.

Because it's there.

(2) Physical realization of Phase Modulation.

Just make an ordinary reactance modulator and detune it a little.

(3) Can a DC source be used as a supply to PC. [As far as I know.....a
UPS does convert it to DC from the AC mains]

No, you need four.

Can anybody plzz give me the answer of these two
questions...........Thanx.....Diba

Why can't you ask the teacher? ;-)
--
Cheers!
Rich

 

[Captain]

"Hollenburg" <ha_ha_he_he@rediffmail.com> wrote in message
news:b8c432a3.0407050034.7e0e20a5@posting.google.com...

Hi,
Recently in an interview one of my friend was asked some
questions.....
(1) If Digital Communication has so many advantages over Analog
communication then why do we use Analog Communication. My friend
answered simplicity to implement but they were looking for some more
specific answers.
(2) Physical realization of Phase Modulation.
(3) Can a DC source be used as a supply to PC. [As far as I know.....a
UPS does convert it to DC from the AC mains]

Can anybody plzz give me the answer of these two
questions...........Thanx.....Diba

Diba,

There are two main reasons to study analog electronics:

1) Everything actually transmitted is analog. This includes photonics and
wireless. If you study, for example, a DSL transmission from your local
telephone company's Central Office (CO) to your home, you will find that it
consists of a series of tones, each of which is phase and amplitude
modulated to carry a digital byte. The contents are digital, but the actual
transmission is totally analog. The drivers which send the signal down the
line are analog, as are the receivers at the other end.

So, all communication is actually analog in nature, In fact, digital
communications are always carried on an analog medium.

2) Your friends are actually quite correct. So look for examples of the
greater simplicity of analog.

As to the other two, come on now, look them up! Hint - Quadrature Amplitude
Modulation -

Cap

 

[Bob Myers]

"Captain" <Captain7@rochester.rr.com> wrote in message
news:I0QGc.16862$bp1.2456@twister.nyroc.rr.com...

(1) If Digital Communication has so many advantages over Analog
communication then why do we use Analog Communication. My friend
answered simplicity to implement but they were looking for some more
specific answers.

1) Everything actually transmitted is analog.

Well, not quite. This touches on one of my personal hot buttons, which
is a widespread confusion about that the terms "analog" and "digital"
really mean.

"Analog" does NOT equate to either "continuous" or "linear", and in
fact there are examples of "analog" communications schemes which
are neither. "Analog" simply means that the information being carried
is encoded on to the signal in such a way that a given parameter of
the signal - the voltage, say - is varying in a manner that is
*analogous* to the original information. In an AM radio signal, for
instance, the amplitude of the carrier is changing in a manner analogous
to the variations in the original sound waves. In a standard analog video
signal, the voltage of the signal varies according to the luminance in
the original image. It is incorrect to say that "everything is analog" from
this perspective, just as it is incorrect to say that "everything is really
digital" (often heard from those who are invoking the discrete nature
of things, per quantum mechanics and such). "Digital" simply means
that the information is being encoded in such a way that the signal
states are to be interpreted as corresponding to numeric values (or
more broadly, some other such symbolic representation) rather than
being a "drawing" of the original information.

The reason we study "analog" communication has to do with an
incorrect assumption that is embedded in the original question.
"Digital" communication is NOT inherently superior in all aspects
as compared with "analog" communication; the superiority of one
over the other depends on the specific requirements of the application
being considered, and the specifics of the encoding schemes, analog
OR digital, being compared. What most people think of as
"digital" communications (straight binary encoding, transmitted
serially in a given channel) typically will have advantages in terms of
noise immunity, but it actually horribly inefficient in terms of its
efficiency
- the amount of information that can be transmitted per second in a given
bandwidth. It also suffers from a sort of "cliff effect" vs. many common
"analog" schemes - meaning that this form of digital communications will
remain essentially "perfect" (lossless) right up to a certain limit in the
noise
level - beyond which, EVERYTHING is lost (as opposed to common
analog systems, which degrade more gracefully in the presence of noise).

So - the bottom line here is that it just ain't that simple. We study both
analog AND digital communications because each still has its place.
There's really no such thing as an "analog" or "digital" SIGNAL, when
you get right down to it - it's all just electricity or EM waves. What
makes
it "analog" or "digital" is the method used to encode the information
carried by that signal, and therefore how it is supposed to be interpreted
by the receiver.


Bob M.

 

[Dbowey]

Bob posted:
<< "Captain" <Captain7@rochester.rr.com> wrote in message
news:I0QGc.16862$bp1.2456@twister.nyroc.rr.com...

(1) If Digital Communication has so many advantages over Analog
communication then why do we use Analog Communication. My friend
answered simplicity to implement but they were looking for some more
specific answers.

1) Everything actually transmitted is analog.

Well, not quite. This touches on one of my personal hot buttons, which
is a widespread confusion about that the terms "analog" and "digital"
really mean.

"Analog" does NOT equate to either "continuous" or "linear", and in
fact there are examples of "analog" communications schemes which
are neither. "Analog" simply means that the information being carried
is encoded on to the signal in such a way that a given parameter of
the signal - the voltage, say - is varying in a manner that is
*analogous* to the original information. In an AM radio signal, for
instance, the amplitude of the carrier is changing in a manner analogous
to the variations in the original sound waves. In a standard analog video
signal, the voltage of the signal varies according to the luminance in the
original image. It is incorrect to say that "everything is analog" from this
perspective, just as it is incorrect to say that "everything is really digital"
(often heard from those who are invoking the discrete nature of things, per
quantum mechanics and such). "Digital" simply means that the information is
being encoded in such a way that the signal
states are to be interpreted as corresponding to numeric values (or
more broadly, some other such symbolic representation) rather than
being a "drawing" of the original information.

The reason we study "analog" communication has to do with an
incorrect assumption that is embedded in the original question.
"Digital" communication is NOT inherently superior in all aspects
as compared with "analog" communication; the superiority of one
over the other depends on the specific requirements of the application
being considered, and the specifics of the encoding schemes, analog
OR digital, being compared. What most people think of as
"digital" communications (straight binary encoding, transmitted
serially in a given channel) typically will have advantages in terms of
noise immunity, but it actually horribly inefficient in terms of its
efficiency - the amount of information that can be transmitted per second in a
given bandwidth. It also suffers from a sort of "cliff effect" vs. many common
"analog" schemes - meaning that this form of digital communications will
remain essentially "perfect" (lossless) right up to a certain limit in the
noise level - beyond which, EVERYTHING is lost (as opposed to common analog
systems, which degrade more gracefully in the presence of noise).

So - the bottom line here is that it just ain't that simple. We study both
analog AND digital communications because each still has its place.
There's really no such thing as an "analog" or "digital" SIGNAL, when
you get right down to it - it's all just electricity or EM waves. What
makes it "analog" or "digital" is the method used to encode the information
carried by that signal, and therefore how it is supposed to be interpreted by
the receiver.
I believe that a designer who understands electronics will not think in terms
of "what's analog and what's digital." She/he will use whatever design skills
will get the job done.

Speaking of hot buttons, you make a false statement in
"In an AM radio signal, for instance, the amplitude of the carrier
is changing in a manner analogous to the variations in the original
sound waves."

The Carrier does not vary - it is constant. The sidebands, which are generated
in the process of modulation, are analogous to the original audio signal.

Don

 

[Bob Myers]

"Dbowey" <dbowey@aol.com> wrote in message
news:20040707154410.05846.00001377@mb-m05.aol.com...

I believe that a designer who understands electronics will not think in
terms
of "what's analog and what's digital." She/he will use whatever design
skills
will get the job done.

Sure - but the sign on the door here is still "sci.electronics.basics",
and I was assuming from the original post that we weren't exactly
working at the "experienced designer" level.

Speaking of hot buttons, you make a false statement in
"In an AM radio signal, for instance, the amplitude of the carrier
is changing in a manner analogous to the variations in the original
sound waves."

True, and a good point; however, again that's the way it's normally
thought of at the beginner level, and you don't really get to the
constant-carrier-amplitude (or rather, the presence of a constant-
amplitude component at the carrier frequency in the transmitted
signal) idea without a bit more understanding of the math than you'll
usually get in the "AM in one paragraph" sort of description. THERE,
you get the standard time-domain "scope display" sort of picture,
with an RF signal whose amplitude is varying with the audio.

Bob M.