|
Cellular forums Home > Archive > Cingular cell phone service > July 2007 > Re: AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low
You are viewing an archived Text-only version of the thread.
To view this thread in it's original format and/or if you want to reply to
this thread please [click here]
| Author |
Re: AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low
|
|
| cledus 2007-06-30, 10:33 pm |
| Radium wrote:
> Hi:
>
> Please don't be annoyed/offended by my question as I decreased the
> modulation frequency to where it would actually be realistic.
>
> I have a very weird question about electromagnetic radiation,
> carriers, and modulators.
>
> Is it mathematically-possible to carry a modulator signal [in this
> case, a pure-sine-wave-tone] with a frequency of 20 KHz and an
> amplitude of 1-watt-per-meter-squared on a AM carrier signal whose
> frequency is 10^-(1,000,000,000-to-the-power-10^1,000,000,000)
> nanocycle* every 10^1,000,000,000-to-the-power-10^1,000,000,000 giga-
> eons and whose amplitude is a minimum of 10^1,000,000,000-to-the-
> power-10^1,000,000,000 gigaphotons per 10^-(1,000,000,000-to-the-
> power-10^1,000,000,000) nanosecond?
>
> If it is not mathematically-possible, then please explain why.
>
> 10^-(1,000,000,000-to-the-power-10^1,000,000,000) second is an
> extremely short amount of time. 10^-(1,000,000,000-to-the-
> power-10^1,000,000,000) nanosecond is even shorter because a
> nanosecond is shorter than a second.
>
> Giga-eon = a billion eons
>
> Eon = a billion years
>
> *nanocycle = billionth of a cycle
>
> Gigaphoton = a billion photons
>
> 10^1,000,000,000-to-the-power-10^1,000,000,000 -- now that is one
> large large number.
>
> 10^1,000,000,000 = 10-to-the-power-1,000,000,000
>
> So you get:
>
> (10-to-the-power-1,000,000,000) to the power (10-to-the-
> power-1,000,000,000)
>
> 10^-(1,000,000,000-to-the-power-10^1,000,000,000) = 10^-(10-to-the-
> power-1,000,000,000)-to-the-power-(10-to-the-power-1,000,000,000)
>
> 10^-(10-to-the-power-1,000,000,000) to the power (10-to-the-
> power-1,000,000,000) is an extremely small number at it equals 10-to-
> the-power-NEGATIVE-[(10-to-the-power-1,000,000,000) to the power (10-
> to-the-power-1,000,000,000)]
>
> No offense but please respond with reasonable answers & keep out the
> jokes, off-topic nonsense, taunts, insults, and trivializations. I am
> really interested in this.
>
>
> Thanks,
>
> Radium
>
The fundamental answer is no, it is not possible to generate AM where
the baseband signal is a pure 20 kHz sinewave and Fc<20kHz. The reason
is that the modulated waveform consists of the sum of a sinewave at Fc,
a sinewave at Fc+20kHz, and a sinewave at Fc-20kHz. If Fc<20kHz then
one of the components becomes a "negative" frequency. So the carrier
must be greater than the baseband signal to prevent this.
It is conceivable that you could make Fc a miniscule number higher than
20kHz. However, if you want to radiate the signal efficiently, you will
need an antenna that is miles long. That is why most radios operate
with carrier frequencies much higher than the audio range. Antennas
become much more practical at frequencies in the MHz range.
You might enjoy a good book that provides fundamentals of electronics
and radio. Pick up a copy of the ARRL Handbook (www.arrl.org), for
example. That should help you pick up some of these concepts.
| |
| cledus 2007-07-01, 10:33 pm |
| Ian Jackson wrote:
> In message <EXChi.23350$C96.1422@newssvr23.news.prodigy.net>, cledus
> <cledus@noemail.net> writes
> I'm afraid that this is not correct. The 'laws of physics' don't
> suddenly stop working if the carrier is lower than the modulating
> frequency. However, there's no need to get into complicated mathematics
> to illustrate this. Here is a simple example:
>
> (a) If you modulate a 10MHz carrier with a 1MHz signal, you will produce
> two new signals (the sidebands) at the difference frequency of 10 minus
> 1 = 9MHz, and the sum frequency of 10 plus 1 = 11MHz. So you have the
> original carrier at 10MHz, and sideband signals at 9 and 11MHz (with a
> balanced modulator - no carrier - only 9 and 11MHz).
>
> (b) If you modulate a 1MHz carrier with a 10MHz signal, you will produce
> two new signals (the sidebands) at the difference frequency of 1 minus
> 10 = minus 9MHz, and the sum frequency of 1 plus 10 = 11MHz. The
> implication of the negative 'minus 9' MHz signal is that the phase of
> the 9MHz signal is inverted, ie 180 degrees out-of-phase from 9MHz
> produced in (a). So you have the original carrier at 1MHz, and sidebands
> at 9 and 11MHz (again, with a balanced modulator - no carrier - only 9
> and 11MHz).
>
> The waveforms of the full composite AM signals of (a) and (b) will look
> quite different. The carriers are at different frequencies, and the
> phase of the 9MHz signal is inverted. However, with a double-balanced
> modulator, you will only have the 9 and 11MHz signal so, surprisingly,
> the resulting signals of (a) and (b) will look the same.
>
> [Note that, in practice, many double-balanced modulators/mixers put
> loads of unwanted signals - mainly due the effects of harmonic mixing.
> However, the basic 'laws of physics' still apply.]
>
> Finally, although I have spoken with great authority, when I get a
> chance I WILL be doing at test with a tobacco-tin double-balanced mixer,
> a couple of signal generators and a spectrum analyser - just to make
> sure that I'm not talking rubbish. In the meantime, I'm sure that some
> will correct me if I'm wrong.
>
> Ian.
Ian,
I believe your analysis is correct. But if you expect to build a
receiver that uses a filter centered at 1 MHz with a BW of 20+ MHz to
recover a DSB AM signal, I don't believe that the DBM approach will
accomplish this. With your approach, you could filter out the sidebands
by centering a filter around 10 MHz (the baseband freq). This could be
used to recover the baseband 10 MHz signal. But the OP asked about AM
of a carrier at very low frequencies. Good explanation of what happens
when using a DBM, though.
Regards,
-C
| |
| John Smith 2007-07-02, 10:33 am |
| Don Bowey wrote:
> ...
> Would you please come and ask nicely. I don't like how you put your order.
>
Get back on your meds and cease and desist from bothering the other
mental patients--else you get the straight jacket next! <grin>
JS
| |
| John Smith 2007-07-02, 3:33 pm |
| Don Bowey wrote:
> ...
Yeah, idiot, lot a proof there.
NO modulation at all, krist, the guy on the other end is only carrying
on a "virtual conversation!"
Excellent use of logic, keep up the good work ...
JS
| |
| John Smith 2007-07-02, 3:33 pm |
| John Smith wrote:
> [stuff]
And, by the way, when using plate modulation on a transmitter, the DC
input to plates of the transmitter has a modulated signal impressed upon
it by a modulation transformer (simply an audio transformer), every watt
of power to the xmitter is so impressed ... The DC voltage/current to
the xmitter contains the voice data--indeed, the exact same data which
is impressed onto the DC on a telephone line (voice/modulation.)
However, the real importance of this will only become clear to you when
you come out from under the influence of whatever it is you are smokin' ...
JS
| |
| John Smith 2007-07-02, 3:33 pm |
| Don Bowey wrote:
> But I know WHY the plate modulated rig creates sidebands, and you still
> don't, because you refuse to learn.
>
Interesting, now you attempt to divert the conversation into the
modulation having been, FINALLY, impressed into the sidebands ...
Hell, it was just such a chore bringing your education up to speed on
this one point, I'd have to be paid to continue your education!
JS
| |
| John Smith 2007-07-02, 3:33 pm |
| Don Bowey wrote:
> You allude to knowing how the sidebands come into being yet you cannot
> provide any clue that you really understand AM, and you continue to think
> microphone current in a telephone loop is the same thing. You're as FOS as
> they come.
>
> I doubt you have fooled anyone on this board with your attempts to look like
> you know more than you really do.
Buddy, you speak about these people being "fooled", interesting term,
implying you consider them fools!
I doubt that is true, they have seen through you in a heartbeat, most,
probably long before now ... I imagine they are just embarrassed for
you--having made such an A$$ of yourself ...
JS
| |
| John Smith 2007-07-02, 10:34 pm |
| Don Bowey wrote:
> ...
> While you continue to allude to skills and knowledge you don't have.
>
> Do you often get away with this useless chest beating?
>
>
You pathetically petty idiot ... I guess you call names because of your
age. Or, others have called you names and it has hurt your ego. Get an
education, grow-up and get off the drugs--you will be able to finally
respect yourself! :-(
Best hope in your therapy!
JS
| |
|
| Don Bowey wrote:
> On 7/2/07 12:29 PM, in article f6bjn4$eja$1@news.albasani.net, "John Smith"
> < assemblywizard@gmail
.com> wrote:
>
>
> Please point out, above, or wherever you wish, where I said they were
> fooled. You can't you POS liar.
>
>
> do.
>
>
> While you continue to allude to skills and knowledge you don't have.
>
> Do you often get away with this useless chest beating?
>
>
| |
|
| Don Bowey wrote:
> On 7/2/07 2:12 PM, in article f6bpo3$tcn$1@news.albasani.net, "John Smith"
> < assemblywizard@gmail
.com> wrote:
>
>
> But POS was intended for guys like you.
>
> Ok! Again, you win. Please enjoy your blissful ignorance with my good
> wishes.
>
> Finis
>
>
|
|
|
|
|