Why isn't FM video used?
Radium
Video signals for NTSC, PAL, and SECAM television are transmitted on AM
carriers. Why?
AM is sensitive to static. Electrical disturbances -- such the the EM
waves emitted florescent bulbs -- will cause distortions on any AM
receiver. The video reception will be altered due to static.
Why not use FM carriers to broadcast video signals? It would be
static-free.
Regards,
Radium
Lord Garth
"Radium" <gluc...@excite.com> wrote in message
news:1158031494....@h48g2000cwc.googlegroups.com...
Better look into how the L-R signal is modulated at any FM station in the
USA.
Phil Allison
"Lord Garth"
>
> Better look into how the L-R signal is modulated at any FM station in the
> USA.
>
** Why ??
It still frequency modulates the carrier, but above the audio band.
........ Phil
John Larkin
It would use too much bandwidth/spectrum.
John
BobG
they send down the cable right? MPEG compressed digital video and
audio, 4 or 5 megabits a sec?
Michael Black
All those "build your own satellite receivers" of 20 years ago had
wideband discriminators of some kind, it was kind of amusing that
they could have an IF of 70MHz and still have suitable selectivity.
Some people playing with amateur radio tv have played with FM for
the video. Though, nobody even considered it until about 15 or 20 years
ago, after monitors were common so you'd just build up a receiver from
scratch. When regular TVs were the only game in town, they never
looked beyond AM for the video.
Michael
Bob Eld
Simple answer: FM is wasteful of bandwidth with other things equal. The
video signal needs about 3-1/2Mhz of bandwidh. It would be difficult to get
this with FM unless the channel spacing was maybe 10 to 20MHz depending on
modulation index.
Also note that digital modulation is also AM where the phase also carries
information. There are many modulation schemes such as QAM, etc. but they
all use AM as the backbone. The idea is to cram as many bits into a Hertz of
bandwidth as possible. This is done by utilizing both the amplitude and
phase in the modulation scheme.
Bob
Radium
Bob Eld wrote:
> "Radium" <gluc...@excite.com> wrote in message
> news:1158031494....@h48g2000cwc.googlegroups.com...
> > Hi:
> >
> > Video signals for NTSC, PAL, and SECAM television are transmitted on AM
> > carriers. Why?
> >
> > AM is sensitive to static. Electrical disturbances -- such the the EM
> > waves emitted florescent bulbs -- will cause distortions on any AM
> > receiver. The video reception will be altered due to static.
> >
> > Why not use FM carriers to broadcast video signals? It would be
> > static-free.
> >
> >
> > Regards,
> >
> > Radium
>
> Simple answer: FM is wasteful of bandwidth with other things equal. The
> video signal needs about 3-1/2Mhz of bandwidh. It would be difficult to get
> this with FM unless the channel spacing was maybe 10 to 20MHz depending on
> modulation index.
>
What if the WMV [Windows Media Video] digital compression is used and
the color resolution is decrease sufficiently?
> Also note that digital modulation is also AM where the phase also carries
> information. There are many modulation schemes such as QAM, etc. but they
> all use AM as the backbone. The idea is to cram as many bits into a Hertz of
> bandwidth as possible. This is done by utilizing both the amplitude and
> phase in the modulation scheme.
> Bob
Is it possible for digital modulation to use FM as a backbone? Has this
ever been done?
John Fields
>Bob Eld wrote:
>> "Radium" <gluc...@excite.com> wrote in message
>> news:1158031494....@h48g2000cwc.googlegroups.com...
>> > Hi:
>> >
>> > Video signals for NTSC, PAL, and SECAM television are transmitted on AM
>> > carriers. Why?
---
Because we handle visual noise much better than we handle audio
noise.
---
>> > AM is sensitive to static. Electrical disturbances -- such the the EM
>> > waves emitted florescent bulbs -- will cause distortions on any AM
>> > receiver. The video reception will be altered due to static.
---
True, but the nature of the radiated interference from fluorescent
lamps will be limited by the species of the harmonics generated and
the selectivity of the receiver.
120Hz and its harmonics are not likely to cause me any grief when
I'm watching TV, and I often run about a kilowatt's worth of
fluorescent lamps when I'm watching TV with no ill effect.
>> >
>> > Why not use FM carriers to broadcast video signals? It would be
>> > static-free.
>> >
>> >
>> > Regards,
>> >
>> > Radium
>>
>
>> Simple answer: FM is wasteful of bandwidth with other things equal. The
>> video signal needs about 3-1/2Mhz of bandwidh. It would be difficult to get
>> this with FM unless the channel spacing was maybe 10 to 20MHz depending on
>> modulation index.
>>
>
>What if the WMV [Windows Media Video] digital compression is used and
>the color resolution is decrease sufficiently?
>
>> Also note that digital modulation is also AM where the phase also carries
>> information. There are many modulation schemes such as QAM, etc. but they
>> all use AM as the backbone. The idea is to cram as many bits into a Hertz of
>> bandwidth as possible. This is done by utilizing both the amplitude and
>> phase in the modulation scheme.
>> Bob
>
>Is it possible for digital modulation to use FM as a backbone? Has this
>ever been done?
--
John Fields
Professional Circuit Designer
Dana
"John Fields" <jfi...@austininstruments.com> wrote in message
news:ge1ji21cauolcleo4...@4ax.com...
You can use one form of Modulation (digital) to modulate another form of
modulation (fm)
I think you have not digested what the person said about QAM above.
Depends on what you want to do will determine what kind of backbone stystem
you would use.
Radium
By "digital" you mean PCM?
>
> I think you have not digested what the person said about QAM above.
QAM uses two AM carriers that are 90 degrees out-of-phase with each
other.
>
> Depends on what you want to do will determine what kind of backbone stystem
> you would use.
Does PCM have to have an AM component? Can't PCM have an FM component
instead?
Dana
I used digital as you used digital above.
>
> >
> > I think you have not digested what the person said about QAM above.
>
> QAM uses two AM carriers that are 90 degrees out-of-phase with each
> other.
It went over your head. You asked if you can use digital modulation on a
frequemcy modulation system. QAM can be considered as a form of digital
modulation. So can FSK as someone else has pointed out. FSK answers your
question about FM being used.
http://www.intel.com/netcomms/technologies/wimax/303788.pdf#search=%22is%20qam%20a%20digital%20modulation%22
>
As for video and FM, FM is often used in fiber optics for video signals, and
there are products that I know of for security cameras that transmit video
via FM links.
I suggest you try GOOGLE.
> >
> > Depends on what you want to do will determine what kind of backbone
stystem
> > you would use.
>
> Does PCM have to have an AM component? Can't PCM have an FM component
> instead?
PCM is a digital representation of an ANALOG signal.
You are confusing your terms here.
Eeyore
Radium wrote:
It doesn't need to be.
Graham
John Fields
>Does PCM have to have an AM component? Can't PCM have an FM component
>instead?
---
http://www.google.com/search?hl=en&q=modulation
http://en.wikipedia.org/wiki/Modulation
Ron Capik
> < ...snip... >
>
> Does PCM have to have an AM component? Can't PCM have an FM component
> instead?
>
So, in your words, what are the various "components" of AM, FM, and PCM ?
Now, what is the degree of orthogonality of those components?
Later...
--
Bob Eld
Most digital modulation schemes use phase as a component of the modulation
as well as amplitude. Phase Modulation and Frequency Modulation, FM are
related. One is the differential of the other. Think of it this way: If you
change the phase of a wave, you instantaneously compress or expand the wave
which is a short term change in frequency. So, in a sense, Frequency
Modulation is a part of many digital schemes. Howerver, except in
rudimentary forms like FSK (frequency shift keying), true FM is not used.
Again it comes down to cramming as many bits of information into each Hertz
of bandwidth as possible and Phase Modulation has a defintie edge over FM.
There are complicated mathematical reasons for this.
To answer your question, it would be possible to combine AM and FM to form a
digital constellation of bit values but I don't know of any commercial
scheme that does this. I suspect that communication engineers have tried
everything and picked what works best.
Bob
Radium
Beleive it or not, the French use AM for the TV's audio carrier, while
using FM for the video carrier. Broadcast System L
Radium
I think they are phasing this system-L out
Bob Myers
> Beleive it or not, the French use AM for the TV's audio carrier, while
> using FM for the video carrier. Broadcast System L
Not so; FM is used only for the chroma components, not the
luminance (Y) signal (which is what lives on the "video" carrier),
and only one chroma signal is sent per line (that's the whole
SECAM thing). FM's still a bandwidth hog, and can't be used
for the full-bandwidth Y signal in any analog TV broadcast
system.
Bob M.