Reply by Glen Herrmannsfeldt●August 1, 20032003-08-01
"Jerry Avins" <jya@ieee.org> wrote in message
news:3F2964A0.471AF151@ieee.org...
> Glen Herrmannsfeldt wrote:
> >
> > "Clay S. Turner" <physicsNOOOOSPPPPAMMMM@bellsouth.net> wrote in message
> > news:%i8Wa.15255$5O3.8866@fe03.atl2.webusenet.com...
> > >
> > > "Glen Herrmannsfeldt" <gah@ugcs.caltech.edu> wrote in message
> > > news:b4zUa.135069$wk6.35585@rwcrnsc52.ops.asp.att.net...
> > >
> > > snip
> > >
> > > >
> > > > (WWV has a transmitter with a 20KHz carrier trying to cover the
whole US
> > > > with one transmitter. That is the lowest I know for a real radio
> > > > transmission. It might even be FSK.)
> > >
> > > Hello Glen, et. al.,
> > >
> > > The US Navy has a transmitter at 76Hz which offers worldwide coverage
for
> > > its submarine fleet.
> >
> > I forgot about that one.
> >
> > We did have a submarine homework problem in an optics class once which
> > needed the index of refraction of water at 15kHz. (It is about 9.)
That
> > may have been before the 76Hz transmitter.
> That monster -- or at least experiments leading to it -- dated to around
> 1960, I believe.
The 15kHz submarine problem was about 1978. I don't know when it actually
existed, if it did. (It was a homework problem, which may not represent a
real system, though I thought it did.)
-- glen
Reply by Jerry Avins●July 31, 20032003-07-31
Glen Herrmannsfeldt wrote:
>
> "Clay S. Turner" <physicsNOOOOSPPPPAMMMM@bellsouth.net> wrote in message
> news:%i8Wa.15255$5O3.8866@fe03.atl2.webusenet.com...
> >
> > "Glen Herrmannsfeldt" <gah@ugcs.caltech.edu> wrote in message
> > news:b4zUa.135069$wk6.35585@rwcrnsc52.ops.asp.att.net...
> >
> > snip
> >
> > >
> > > (WWV has a transmitter with a 20KHz carrier trying to cover the whole US
> > > with one transmitter. That is the lowest I know for a real radio
> > > transmission. It might even be FSK.)
> >
> > Hello Glen, et. al.,
> >
> > The US Navy has a transmitter at 76Hz which offers worldwide coverage for
> > its submarine fleet.
>
> I forgot about that one.
>
> We did have a submarine homework problem in an optics class once which
> needed the index of refraction of water at 15kHz. (It is about 9.) That
> may have been before the 76Hz transmitter.
>
> -- glen
That monster -- or at least experiments leading to it -- dated to around
1960, I believe.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Glen Herrmannsfeldt●July 31, 20032003-07-31
"Clay S. Turner" <physicsNOOOOSPPPPAMMMM@bellsouth.net> wrote in message
news:%i8Wa.15255$5O3.8866@fe03.atl2.webusenet.com...
>
> "Glen Herrmannsfeldt" <gah@ugcs.caltech.edu> wrote in message
> news:b4zUa.135069$wk6.35585@rwcrnsc52.ops.asp.att.net...
>
> snip
>
> >
> > (WWV has a transmitter with a 20KHz carrier trying to cover the whole US
> > with one transmitter. That is the lowest I know for a real radio
> > transmission. It might even be FSK.)
>
> Hello Glen, et. al.,
>
> The US Navy has a transmitter at 76Hz which offers worldwide coverage for
> its submarine fleet.
I forgot about that one.
We did have a submarine homework problem in an optics class once which
needed the index of refraction of water at 15kHz. (It is about 9.) That
may have been before the 76Hz transmitter.
-- glen
Reply by Jerry Avins●July 31, 20032003-07-31
"Clay S. Turner" wrote:
>
> "Glen Herrmannsfeldt" <gah@ugcs.caltech.edu> wrote in message
> news:b4zUa.135069$wk6.35585@rwcrnsc52.ops.asp.att.net...
>
> snip
>
> >
> > (WWV has a transmitter with a 20KHz carrier trying to cover the whole US
> > with one transmitter. That is the lowest I know for a real radio
> > transmission. It might even be FSK.)
>
> Hello Glen, et. al.,
>
> The US Navy has a transmitter at 76Hz which offers worldwide coverage for
> its submarine fleet.
>
> See
> http://www.vlf.it/submarine/sbmarine.html
> for details
>
> Clay
>
> >
> > -- glen
> >
> >
They have a pretty big antenna for it too! Does anyone know the maximum
bit rate or how far out significant sidebands extend?
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Clay S. Turner●July 31, 20032003-07-31
"Glen Herrmannsfeldt" <gah@ugcs.caltech.edu> wrote in message
news:b4zUa.135069$wk6.35585@rwcrnsc52.ops.asp.att.net...
snip
>
> (WWV has a transmitter with a 20KHz carrier trying to cover the whole US
> with one transmitter. That is the lowest I know for a real radio
> transmission. It might even be FSK.)
Hello Glen, et. al.,
The US Navy has a transmitter at 76Hz which offers worldwide coverage for
its submarine fleet.
See
http://www.vlf.it/submarine/sbmarine.html
for details
Clay
>
> -- glen
>
>
Reply by Glen Herrmannsfeldt●July 28, 20032003-07-28
"Baretto" <suhnas1999@yahoo.co.uk> wrote in message
news:5b98244c.0307272144.45c58492@posting.google.com...
> I think there is a confusion here,
> Always a low signal which is called a modulating signal is up
> converted using a carrier which is at higher frequency..Now lets say a
> speech signal at 0-4 khz..fm = 4KHz(max mod freq) when this has to be
> sent over a channel then it is upconverted using a higher freq carrier
> lats say 10MHz. when this is done the bandwidth occupied here will be
> twice the modulating freq..at 100MHz which is from (fc-fm) to (fc+fm)
I think you are right, but a different question was being asked.
The question is how high can the modulation signal be for a given carrier
frequency, for FM (FSK) modulation.
Now, it is normal for the carrier to be higher than the modulation rate,
maybe in some cases equal to the modulation rate.
There was a claim that there is no limit to the modulation rate, so I took
an extreme example, to test the claim.
The (fc-fm) and (fc+fm) works well for AM signals, but FM (FSK) was being
discussed. Theoretically, the bandwidth is infinite, but practically, it
falls of fast enough that a reasonable bandwidth can be defined.
-- glen
Reply by Baretto●July 28, 20032003-07-28
> I was answering a claim that there was no limit to the modulating frequency.
> If you don't like those numbers, how about a 1MHz carrier, and modulating at
> 1THz. Well, maybe 1GHz is enough. I agree that 1Hz doesn't make a very
> good carrier.
>
> (WWV has a transmitter with a 20KHz carrier trying to cover the whole US
> with one transmitter. That is the lowest I know for a real radio
> transmission. It might even be FSK.)
>
> -- glen
I think there is a confusion here,
Always a low signal which is called a modulating signal is up
converted using a carrier which is at higher frequency..Now lets say a
speech signal at 0-4 khz..fm = 4KHz(max mod freq) when this has to be
sent over a channel then it is upconverted using a higher freq carrier
lats say 10MHz. when this is done the bandwidth occupied here will be
twice the modulating freq..at 100MHz which is from (fc-fm) to (fc+fm)
..Glen carrier is not modulated but modutating signal is modulated to
get a modulated signal using a higher frequency carrier...in the
example u have given 1MHz is again a modulating signal and 1THz is a
carrier..There are cases where more than one leven of up conversion or
downconversion is used,in which case it is called as IF levels...where
it is said that 1MHz IF is again up converted to 1 1THz...
>I was answering a claim that there was no limit to the modulating
frequency.
there is a limit to this also...ur modulation freq cannot exceed the
carrier frequency
raj
Reply by Randy Yates●July 28, 20032003-07-28
glen herrmannsfeldt wrote:
>
> "Randy Yates" <yates@ieee.org> wrote in message
> news:567ce618.0307241135.76c03856@posting.google.com...
> > "glen herrmannsfeldt" <gah@ugcs.caltech.edu> wrote in message
> news:<6hETa.115923$GL4.30071@rwcrnsc53>...
> > > "Randy Yates" <yates@ieee.org> wrote in message
> > > news:567ce618.0307231342.4637d16f@posting.google.com...
> > > > aberdonian_2000@yahoo.com (Tom) wrote in message
> > > news:<e1b1658f.0307221244.575e9f86@posting.google.com>...
> > > > > If I have a digital FM system do you have any background on the max
> > > > > bit rate you can achieve for a given depth of modulation? eg for
> > > > > 250kHz depth of modulation I can achieve only 500kb/s. Does this
> sound
> > > > > right? This must be pretty basic stuff I am sure and related to
> > > > > Shannons law somewhere.
> > >
> > > > If you are talking about FSK, then there is no limit. The problem
> > > > is that the bandwidth just keeps getting bigger and bigger. If
> > > > you had asked what the maximum bitrate is for a given bandwidth,
> > > > then an answer could be negotiated.
> > >
> > > Well, I think when you exceed, or even get close to, the carrier
> frequency
> > > you should not call it FSK anymore. It may be that, technically, you
> can
> > > still decode the bits from the sidebands, it isn't because you are
> > > demodulating the FM signal.
> >
> > Why isn't it? If I quadrature downconvert to baseband and then
> > compute the derivative of the instantaneous phase, isn't that
> > demodulating an FM signal?
>
> Say the carrier was 1Hz, FM modulated at 1MHz. Now you want to quadrature
> downconvert to 0Hz? Hmm. Where do you get the reference signal for the
> downconverter? How accurate is the reference signal? Does it make sense
> to call a 1Hz signal modulated at 1MHz FSK?
I was presuming that we were far enough away from DC that this type
of problem doesn't happen.
--
% Randy Yates % "...the answer lies within your soul
%% Fuquay-Varina, NC % 'cause no one knows which side
%%% 919-577-9882 % the coin will fall."
%%%% <yates@ieee.org> % 'Big Wheels', *Out of the Blue*, ELO
http://home.earthlink.net/~yatescr
Reply by Glen Herrmannsfeldt●July 26, 20032003-07-26
"Baretto" <suhnas1999@yahoo.co.uk> wrote in message
news:5b98244c.0307260032.462426c2@posting.google.com...
> > > Why isn't it? If I quadrature downconvert to baseband and then
> > > compute the derivative of the instantaneous phase, isn't that
> > > demodulating an FM signal?
> >
> > Say the carrier was 1Hz, FM modulated at 1MHz. Now you want to
quadrature
> > downconvert to 0Hz? Hmm. Where do you get the reference signal for
the
> > downconverter? How accurate is the reference signal? Does it make
sense
> > to call a 1Hz signal modulated at 1MHz FSK?
> 1 Hz is not carrier 1 Mhz is a carrier on which the information is
> carried. 1 Hz is the modulating signal.
> Reference signal for the down converter can be got from crystal
> oscillators which has to be accurate and precise and the drifts should
> be very small which is measured in ppm(parts per million) Normally
> crystals have a tendency to drift at ~25 ppm. to compensate for this
> drifts plls are used.
I was answering a claim that there was no limit to the modulating frequency.
If you don't like those numbers, how about a 1MHz carrier, and modulating at
1THz. Well, maybe 1GHz is enough. I agree that 1Hz doesn't make a very
good carrier.
(WWV has a transmitter with a 20KHz carrier trying to cover the whole US
with one transmitter. That is the lowest I know for a real radio
transmission. It might even be FSK.)
-- glen
Reply by Baretto●July 26, 20032003-07-26
> > Why isn't it? If I quadrature downconvert to baseband and then
> > compute the derivative of the instantaneous phase, isn't that
> > demodulating an FM signal?
>
> Say the carrier was 1Hz, FM modulated at 1MHz. Now you want to quadrature
> downconvert to 0Hz? Hmm. Where do you get the reference signal for the
> downconverter? How accurate is the reference signal? Does it make sense
> to call a 1Hz signal modulated at 1MHz FSK?
>
> -- glen
Glen
1 Hz is not carrier 1 Mhz is a carrier on which the information is
carried. 1 Hz is the modulating signal.
Reference signal for the down converter can be got from crystal
oscillators which has to be accurate and precise and the drifts should
be very small which is measured in ppm(parts per million) Normally
crystals have a tendency to drift at ~25 ppm. to compensate for this
drifts plls are used.