pk :
> >> > 3. the analogue signal is the carrier
am :
> >> The signal carrier is RF
pk:
> > hmm .. so not 0's and 1's .. this would naturally mean issues like freq.
modulation and amplitude modulation would be the issues.. as different from
'bit' manipulation
am :
> >> flowing along ("not through" the medium, like in case of electronic
signal)
pk :
> > oops .. gaps in my understanding .. 'along' and 'through' ? .. i always
understood that the mild milli/pico-watt currents gave RF type waves .. and
that electrons were the particles that did this .. NOT by 'flowing' .. BUT
by making electrons of adjoining atoms of copper shift to adjoining atoms
of copper .. but i would really like to know the reality (it's now 35 years
since i stood 19th in HigherSecondary from science :-( so things are
better understood now, perhaps)
am :
> As an analogy, electronics and movement of electrons is like taking a tube
(conductor) and filling up the tube with the balls (electrons) to its full
capacity and then pushing an extra electron from one end (potential
difference) and out pops the electron oops... the ball at the other end
(circuit). The result is some work done (power applied) and time taken
(resistance). Electrical Engineers will kill me due to this oversimplified
analogy.
>
> RF is like a stream of water flowing and losing its energy along the path
of the flow due to obstruction and roughness in the path (conductor).
>
> If RF was like moving of electrons, how can it travel from antenna to
antenna - one oversimplified guess would be the possible conduction in the
atmosphere.....now how about the antennas on the spaceship and moons and the
free space (vaccum), RF still moves, light still travels without the
conductor. So the next question arises why do we need co-axial .. forget
co-axial why any cable for that matter. The cable is nothing but a guide
path like a pre-dug out channel for a irrigation canal. The digging for the
canal is to provide a guide path for the water to flow to the destination.
Now movement along the path will suffer due to the qualities of the path in
question, how smooth it is, how tight are the bends etc. etc.
am :
> >> the co-axial cable which acts as the RF feeder.
pk :
> > would this mean that the wave propogation (radio freq) through/along the
medium does the work of transferring the 'signal' ?
am :
> Wave propagation to be more precise "electromagnetic wave" propagation
(sound waves are mechanical waves and propagation in that case is little
different) "along" the medium in case of cables (RF feeders / waveguides to
be more precise) and "across" the medium in case of air and free space
provides the way for spread of signal from the origin. "Transfer" of RF
signal is incorrect, as there is no direct or indirect creation of potential
difference at either ends to induce such a "transfer" from one point to
another. There is RF generation, using oscillator electronics and it
"radiates" in all possible directions depending on the radiating element
type i.e "antenna". Now, how and why does another antenna a little or far
away gets this RF energy although having no direct or indirect physical
contact (remember vaccum) ? I invite someone to answer this query ? (just
as a clue - this is a problem of perception).
am:
> >> Therefore, we measure the signal in dB i.e. SNR - Signal to Noise
Ratio.
pk :
> > The signal type is analog definitely as long as it is on the co-axial
cable... hmm .. so it is not in 0's and 1's .. it is non-digital .. an
addition here .. 'signal' or 'freq' by freq/amplitude
modulation/demodulation does not compulsorily mean that it has to be
electron based .. it can be thru short waves/medium waves/microwaves
('disturbances in the radio freq spectrum' which one tunes into) .. and can
also be thru photons .. as in laser based optic fibres .. or even sound
based .. like in the earlier 'modems' on which the telephone hand set had
to be placed .. SNR would apply to all these scenarios.
am :
> Well SNR is a universal principal. The impact can be felt by the sentence
below.
>
> Imagine a world without "Noise" i.e. "unwanted Signals" intefering with
"desired and required signals". All the electrical / electronics, acoustics,
mechanical (in some special fields), biomedical (scan machines etc.), radio
physics, astronomy, communications etc. etc. engineers and professors and
students in the respective fields of today of this world will suddenly loose
their jobs and reasons to exist.
>
> RF is pure energy (electromagnetical in nature) and may be indicatively
understood as analog in nature (i.e. in case, if someone insists on strictly
defining it between either "analog" or "digital").
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