....its not as easy as that though. See, I know that it filters out the
desired frequency, but I was wondering HOW its does it.

I understand that as the RF waves hit the antenna, they cause free electrons
on the antenna to go up and down, and this electrical current (as movement
of electrons causes) is then rectified and amplified (talking simply now),
and pumped out to the speaker. For this example, I think it would be best
to stick with a really simple radio, operating with an Amplitude Modulation.

I imagine the free electrons on the antenna to be very much like a bouy
bouncing around on the sea - going up and down. If there was only one
continuous sinusoidal wave hitting that electron, then it'll be going up and
down quite simply. But then the voice and music we hear is modulated into
that sine wave, so the electron is going up and down, plus "wibbling" about
because of the modulated speech. Taking the bouy example again, I imagine a
tuner very much like a telescope looking at the bouy, and the telescope
bouncing up and down at the same rate. What I should see looking through
the telescope is the bouy bouncing up and down slightly according the music
and voice that has been modulated into it - the carrier wave has been
cancelled out because the telescope and bouy are moving up and down at the
same frequency.

This sounds all right, but if I then continue to take this analogy further,
the bouy (or electron) is moving up and down to MANY frequencies. So even
if I am bouncing up and down at the desired frequency, the chances of me
seeing the bouy in the right place because of all the other frequency waves
are probably nil.

Also, how does the tuner stay in phase with that broadcast, when there are
no synchronisation going on?

To round up, the question is this: how can the tuner only select those
electrons that are ONLY vibrating at the required frequency, when logic
states that the electron must be bouncing around at the combined, additive
effect of all RF waves hitting it!

Anyone care to have a go and answer?

Cheers.

Paul.

On Fri, 21 Jan 2005 20:10:03 GMT, "Paul Hardwick"
wrote:

...its not as easy as that though. See, I know that it filters out the
desired frequency, but I was wondering HOW its does it.

I understand that as the RF waves hit the antenna, they cause free electrons
on the antenna to go up and down, and this electrical current (as movement
of electrons causes) is then rectified and amplified (talking simply now),
and pumped out to the speaker. For this example, I think it would be best
to stick with a really simple radio, operating with an Amplitude Modulation.

I imagine the free electrons on the antenna to be very much like a bouy
bouncing around on the sea - going up and down. If there was only one
continuous sinusoidal wave hitting that electron, then it'll be going up and
down quite simply. But then the voice and music we hear is modulated into
that sine wave, so the electron is going up and down, plus "wibbling" about
because of the modulated speech. Taking the bouy example again, I imagine a
tuner very much like a telescope looking at the bouy, and the telescope
bouncing up and down at the same rate. What I should see looking through
the telescope is the bouy bouncing up and down slightly according the music
and voice that has been modulated into it - the carrier wave has been
cancelled out because the telescope and bouy are moving up and down at the
same frequency.

This sounds all right, but if I then continue to take this analogy further,
the bouy (or electron) is moving up and down to MANY frequencies. So even
if I am bouncing up and down at the desired frequency, the chances of me
seeing the bouy in the right place because of all the other frequency waves
are probably nil.

Also, how does the tuner stay in phase with that broadcast, when there are
no synchronisation going on?

To round up, the question is this: how can the tuner only select those
electrons that are ONLY vibrating at the required frequency, when logic
states that the electron must be bouncing around at the combined, additive
effect of all RF waves hitting it!

Anyone care to have a go and answer?

Cheers.

Paul.

Dear Paul,

It's elementary. Look up the Superposition Theorem. You will find that
in a linear system it is possible to single out any one (or more) of
the existing effects and treat it (them) individually. In other words,
if you restrict the bandwidth of the system so as to study the effects
of only one signal, then that is the only one you will see.
Bob, W9DMK, Dahlgren, VA
Replace "nobody" with my callsign for e-mail
http://www.qsl.net/w9dmk
http://zaffora/f2o.org/W9DMK/W9dmk.html

Paul Hardwick wrote:
To round up, the question is this: how can the tuner only select those
electrons that are ONLY vibrating at the required frequency, when logic
states that the electron must be bouncing around at the combined, additive
effect of all RF waves hitting it!

You are confusing the RF waves with the electron carriers. The easiest
way to stop confusing waves with carriers is to stand on a cliff
looking out over the ocean. (Fitzgerald's Marine Reserve, just north
of Santa Cruz, CA, is an ideal place.) There are all sorts of waves
using the same water molecule carriers. There are big waves rolling
straight in and smaller waves rolling in at an angle. The waves
rolling in reflect off the beach and roll back out to sea. Each of
these waves maintains a separate identity even though they are using
the same individual water molecules as the wave carriers.

RF waves do the same thing - share individual quantum carriers for
any number of waves. All the waves are superposed on each individual
carrier, but each wave maintains its individual identity.

Note that water waves and RF waves are different kinds of waves but
they do share the above limited characteristic concerning carriers.
--
73, Cecil http://www.qsl.net/w5dxp


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