On Jun 30, 3:32 am, "Mike Kaliski" <michael.kali...@tesco.net> wrote:
> "Radium" <gluceg...@gmail.com> wrote in message
>
> news:1183177831.152287.69850@j4g2000prf.googlegrou ps.com...
>
>
>
> > On Jun 29, 9:15 pm, John Smith I <assemblywiz...@gmail.com> wrote:
>
> > > Radium wrote:
>
> > > WTF are you thinking when you describe the 20 Khz signal as, "a
> > > pure-sine-wave-tone] with a frequency of 20 KHz and an
> > > amplitude of 1-watt-per-meter-squared"
>
> > > One square meter of copper wire squared, a squared meter of modulation
> > > xfrmr ... ?
>
> > Sorry that should be 1 X [10^-6] Watts-per-m^2
>
> >http://www.glenbrook.k12.il.us/GBSSC...nd/u11l2b.html
>
> > 1 X [10^-6] Watts-per-m^2 is about the loudness of a "normal
> > conversation" according to the above link.
>
> > F-------------------king typos!!!!!!!!!!
>
> > > Your question sounds like one of a high school physics student
> > > attempting to ask a seemingly logical--yet complex question, and of no
> > > real world value.
>
> > > Your ability at obfuscation is only mundane ...
>
> > > If what you say is true, you have an interest, what is the purpose of
> > > your question?
>
> > My basic question is if I have an AM receiver which receives signals
> > on a carrier frequency of Fc, is it mathematically-possible for me to
> > receive a modulator signal -- on that station -- of a frequency higher
> > than Fc? If not, then why? If not, then how are the submarines which
> > use ELFs [Extremely Low carrier Frequencies around 3 to 30 Hz] able to
> > perform voice communications?
>
> > I just stretched the question out to astronomical extremes. I have a
> > habit of doing that.
>
> Radium
>
> It is not possible to modulate a carrier frequency at a frequency higher
> than the carrier frequency. It wouldn't be a carrier frequency then, the
> higher frequency would become the carrier frequency by default.
>
> ELF communications are carried out at very slow data rates, only a few
> characters per hour at best. Normal demodulation techniques are useless at
> these frequencies and messages are received by what amounts to comparing the
> noise levels on a given very narrow frequency band over long periods.
> Computers are easily capable of performing this task. Messages are generally
> sent as 3 character codes which are then looked up in a code book to read
> the full text of the message. Each message can take half an hour or more to
> send. Only a very limited set of pre arranged messages can be passed but
> this is enough to tell a sub to approach the surface and establish line of
> sight comms direct to a satellite, when more detailed messages can be passed
> securely and at high speeds on higher frequencies (i.e voice and data
> communications). Voice comms cannot be passed at VLF or ELF frequencies.
>
> Nuclear subs are extremely autonomous. There is no quick way to establish
> communications once they have left port and submerged.
>
> It is possible to communicate at a base band frequency of 0Hz. This is what
> happens when you talk down a hard wired telephone or intercom. At a
> telephone exchange (switching centre), the signals from each line are
> modulated onto a higher frequency for onward transmission down a trunk wire
> cable or fibre optic cable. The multiplexed high frequency modulated signals
> are down converted back to audio frequencies once they reach the intended
> destination.
>
> It is also possible to transmit this signal through the air (at incredibly
> low efficiencies and powers). The miles of cables snaking through the
> trenches in World War One were so long that messages could be intercepted by
> the enemy listening in without any direct connection to the system. A good
> ground connection and half a mile of wire rolled out across no mans land was
> sufficient to pick up the signals from the other side. Systems were also
> discovered which employed two widely separated ground connections and
> avoided the need to send men out on a suicide mission to carry wires towards
> the enemy trenches.
>
> Mike G0ULI- Hide quoted text -
>
> - Show quoted text -