🚀 go-pugleaf

On May 27, 9:02 am, GreenXenon <glucege...@gmail.com> wrote:
> Hi:
>
> In frequency modulation:
>
> Increasing the modulator’s amplitude will increase the extent to which
> the carrier frequency varies from baseband. In other words, a larger
> modulation amplitude will cause the carrier to occupy a larger range
> of frequencies than a smaller modulation amplitude
>
> Increasing the modulator’s frequency will increase the rate in which
> the carrier frequency changes. So why is it impossible to transmit a
> higher-frequency modulator signal on a lower-frequency FM carrier
> signal?
>
> I can understand how increasing the modulator’s amplitude will
> increase the bandwidth the carrier uses.
>
> I don’t understand how increasing the modulator’s frequency will
> increase the bandwidth taken up by the carrier. Higher modulator
> frequency simply means the carrier’s frequency will vary faster; it
> will not take up more frequencies unless the mod’s amplitude
> increases.
>
> Thanks,
>
> Green

Here, go down to the example 2, and click on it and I think the dude
might explain it to you -- if you got speakers on your PC.

http://cnx.org/content/m15482/latest/

On May 27, 9:02 am, GreenXenon <glucege...@gmail.com> wrote:
> Hi:
...
> Increasing the modulator’s frequency will increase the rate in which
> the carrier frequency changes. So why is it impossible to transmit a
> higher-frequency modulator signal on a lower-frequency FM carrier
> signal?

It's not impossible but it gets really weird.   You get "negative
frequency" sidebands which wrap around zero and often become noise,
depending how they line up with the non-wrapped sidebands.

>
> I can understand how increasing the modulator’s amplitude will
> increase the bandwidth the carrier uses.
>
> I don’t understand how increasing the modulator’s frequency will
> increase the bandwidth taken up by the carrier. Higher modulator
> frequency simply means the carrier’s frequency will vary faster; it
> will not take up more frequencies unless the mod’s amplitude
> increases.

Somewhere out there, there's a Fourier Transform applet which will
show you what happens to the spectrum.   You get sidebands spaced at
multiples of the modulating frequency.

Executive summary:  FM (and its conjoined twin, phase modulation)
operate by advancing and retarding the progress of the carrier around
its "phase circle" if you will.  The changes in phase-progress
generate frequencies you might not at first expect.  It comes out to C
+- nM for a lot of integer "n".  The amplitude of each one  can be
predicted by something called Bessel Functions.

In article <1a86fd28-bebe-4f09-8d0b-1a6685d01ce3@b34g2000pra.googlegroups.com> GreenXenon <glucegen1x@gmail.com> writes:
>Hi:
>
>In frequency modulation:
>
>Increasing the modulator's amplitude will increase the extent to which
>the carrier frequency varies from baseband. In other words, a larger
>modulation amplitude will cause the carrier to occupy a larger range
>of frequencies than a smaller modulation amplitude
>
>Increasing the modulator's frequency will increase the rate in which
>the carrier frequency changes. So why is it impossible to transmit a
>higher-frequency modulator signal on a lower-frequency FM carrier
>signal?
>
>I can understand how increasing the modulator's amplitude will
>increase the bandwidth the carrier uses.
>
>I don't understand how increasing the modulator's frequency will
>increase the bandwidth taken up by the carrier. Higher modulator
>frequency simply means the carrier's frequency will vary faster; it
>will not take up more frequencies unless the mod's amplitude
>increases.

  Eric answered much of this pretty well, and pointed out pretty well
that changing the frequency of the signal will produce energy at other
frequencies.

  See the first google result from  fm modulation bandwidth  at
http://en.wikipedia.org/wiki/Frequency_modulation

  Other results near the top are also helpful.


	Alan

On Wed, 27 May 2009 09:02:36 -0700 (PDT), GreenXenon
<glucegen1x@gmail.com> wrote:

>Hi:
>
>In frequency modulation:
>
>Increasing the modulator�s amplitude will increase the extent to which
>the carrier frequency varies from baseband. In other words, a larger
>modulation amplitude will cause the carrier to occupy a larger range
>of frequencies than a smaller modulation amplitude

Their is no informatin in the carrier, only in the sidebands so a FM
modulated 15khz tone will take at least 30khz of bandwidth. 




>
>Increasing the modulator�s frequency will increase the rate in which
>the carrier frequency changes. So why is it impossible to transmit a
>higher-frequency modulator signal on a lower-frequency FM carrier
>signal?
>
>I can understand how increasing the modulator�s amplitude will
>increase the bandwidth the carrier uses.
>
>I don�t understand how increasing the modulator�s frequency will
>increase the bandwidth taken up by the carrier. Higher modulator
>frequency simply means the carrier�s frequency will vary faster; it
>will not take up more frequencies unless the mod�s amplitude
>increases.
>
>
>Thanks,
>
>Green

In article <1a86fd28-bebe-4f09-8d0b-1a6685d01ce3@b34g2000pra.googlegroups.com>, GreenXenon <glucegen1x@gmail.com> wrote:
>Hi:
>
>In frequency modulation:
>
>Increasing the modulator=92s amplitude will increase the extent to which
>the carrier frequency varies from baseband. In other words, a larger
>modulation amplitude will cause the carrier to occupy a larger range
>of frequencies than a smaller modulation amplitude
>
>Increasing the modulator=92s frequency will increase the rate in which
>the carrier frequency changes. So why is it impossible to transmit a
>higher-frequency modulator signal on a lower-frequency FM carrier
>signal?
>
>I can understand how increasing the modulator=92s amplitude will
>increase the bandwidth the carrier uses.
>
>I don=92t understand how increasing the modulator=92s frequency will
>increase the bandwidth taken up by the carrier. Higher modulator
>frequency simply means the carrier=92s frequency will vary faster; it
>will not take up more frequencies unless the mod=92s amplitude
>increases.

It would be easiest to see by looking at the spectrum with a spectrum
analyzer. The wider the frequencies will take up a wider space.

greg

In article <1a86fd28-bebe-4f09-8d0b-1a6685d01ce3@b34g2000pra.googlegroups.com>, GreenXenon <glucegen1x@gmail.com> wrote:
>Hi:
>
>In frequency modulation:
>
>Increasing the modulator=92s amplitude will increase the extent to which
>the carrier frequency varies from baseband. In other words, a larger
>modulation amplitude will cause the carrier to occupy a larger range
>of frequencies than a smaller modulation amplitude
>
>Increasing the modulator=92s frequency will increase the rate in which
>the carrier frequency changes. So why is it impossible to transmit a
>higher-frequency modulator signal on a lower-frequency FM carrier
>signal?

If you got 100 mHz carrier a 1 Ghz modulator
it will try to give byproducts which can't be had. A minus 1.1 Ghz is impossible.

Kind of like aliasing I think..

greg 

>I can understand how increasing the modulator=92s amplitude will
>increase the bandwidth the carrier uses.
>
>I don=92t understand how increasing the modulator=92s frequency will
>increase the bandwidth taken up by the carrier. Higher modulator
>frequency simply means the carrier=92s frequency will vary faster; it
>will not take up more frequencies unless the mod=92s amplitude
>increases.
>
>
>Thanks,
>
>Green

In message <gvmlc6$qgb$3@usenet01.srv.cis.pitt.edu>, GregS 
<zekfrivo@zekfrivolous.com> writes
>In article 
><1a86fd28-bebe-4f09-8d0b-1a6685d01ce3@b34g2000pra.googlegroups.com>, 
>GreenXenon <glucegen1x@gmail.com> wrote:
>>Hi:
>>
>>In frequency modulation:
>>
>>Increasing the modulator=92s amplitude will increase the extent to which
>>the carrier frequency varies from baseband. In other words, a larger
>>modulation amplitude will cause the carrier to occupy a larger range
>>of frequencies than a smaller modulation amplitude
>>
>>Increasing the modulator=92s frequency will increase the rate in which
>>the carrier frequency changes. So why is it impossible to transmit a
>>higher-frequency modulator signal on a lower-frequency FM carrier
>>signal?
>
>If you got 100 mHz carrier a 1 Ghz modulator
>it will try to give byproducts which can't be had. A minus 1.1 Ghz is 
>impossible.
>
>Kind of like aliasing I think..

You mean folded sidebands, familiar to all old-school VT engineers.

-- 
If one person has delusions, we call them psychotic. If, however, 1.5 billion
people have delusions we must apparently call them a religious group, and
respect their delusionary state.