"Radium" wrote in message
ups.com...
Hi:

Video signals for NTSC, PAL, and SECAM television are transmitted on
AM carriers.

No, they're not. And there's no such thing as an "AM carrier"
or "FM carrier" to begin with. The carriers themselves are simply
signals at a given frequency. "AM" or "FM" refers to the modulation
IMPOSED on those carriers - in other words, how the information
to be carried is used to modify some aspect of the carrier signal.

In TV, most systems employ a version of AM to carry the luminance
(Y) signal; the color (chroma) information is carried via a somwhat
different version of AM, and the audio is most commonly FM.
The French SECAM system as originally implemented carried the
chroma information on TWO frequency-modulated subcarriers.


My question is, let's say I have a television set that is capable of
receiving and demodulating FM video carrier waves. What would I see on
the TV? I am aware that no company uses FM video. Would I see sawtooth-
like patterns on the screen due to frequency-modulated electric fields
present in the environment?


No.

I'd really like buy a TV with a FM-video receiver; I want to find out
what FM-video disturbances in the SHF [Super High Frequency ]
frequency-range look like. I am sick n' tired of AM video.

AM should be used for analog audio. FM should be used for digital
video.

Nonsense. The choices of AM and FM within the original analog
standard definitions were made for some very, very good reasons.
Digital television is a completely different beast, and is presently
broadcast using two very different modulation schemes - the
U.S. standard (ATSC) using 8-VSB, while the rest of the world
(mostly) will be using COFDM under the DVB-T standard.

Bob M.

On Jun 8, 11:38 am, "Bob Myers" wrote:
"Radium" wrote in message

ups.com...

Hi:

Video signals for NTSC, PAL, and SECAM television are transmitted on
AM carriers.

No, they're not. And there's no such thing as an "AM carrier"
or "FM carrier" to begin with. The carriers themselves are simply
signals at a given frequency. "AM" or "FM" refers to the modulation
IMPOSED on those carriers - in other words, how the information
to be carried is used to modify some aspect of the carrier signal.

Okay. Thanks for clearing this up.

In TV, most systems employ a version of AM to carry the luminance
(Y) signal; the color (chroma) information is carried via a somwhat
different version of AM, and the audio is most commonly FM.
The French SECAM system as originally implemented carried the
chroma information on TWO frequency-modulated subcarriers.

Why not carry the luminance-signal on FM and the audio-signal on AM?

I'd really like buy a TV with a FM-video receiver; I want to find out
what FM-video disturbances in the SHF [Super High Frequency ]
frequency-range look like. I am sick n' tired of AM video.

AM should be used for analog audio. FM should be used for digital
video.

Nonsense. The choices of AM and FM within the original analog
standard definitions were made for some very, very good reasons.
Digital television is a completely different beast, and is presently
broadcast using two very different modulation schemes - the
U.S. standard (ATSC) using 8-VSB, while the rest of the world
(mostly) will be using COFDM under the DVB-T standard.

Couldn't FSK [the digital equivalent of FM] be used for luminance [Y]
signal of the digital video?

"Radium" wrote in message
oups.com...

In TV, most systems employ a version of AM to carry the luminance
(Y) signal; the color (chroma) information is carried via a somwhat
different version of AM, and the audio is most commonly FM.
The French SECAM system as originally implemented carried the
chroma information on TWO frequency-modulated subcarriers.

Why not carry the luminance-signal on FM and the audio-signal on AM?

The reasons (primarily) behind using the AM visual and FM aural signals for
television a

Visual: Bandwidth. Visual uses what is called 'vestigial sideband'. This
means that basically only one sideband carries the modulation, with only a
vestige of the other sideband remaining, thereby reducing the bandwidth
needed for the visual signal by a significant factor. If FM were used, the
entire symmetrical waveform would have to be used, and would use a lot more
bandwidth. (Analog satellite television does/did use FM modulation, on the
order of 36 MHz IIRC, but bandwidth in the GHz ranges isn't at as much of a
premium as on relatively crowded VHF and UHF frequencies

Aural: Coverage. The aural signal (which is sent separately from the visual)
is only about 10% of the power of the visual signal.

"Radium" wrote in message
oups.com...

Why not carry the luminance-signal on FM and the audio-signal on AM?

See the previous post; it's basically a matter of the enormous bandwidth
requirements of FM (note that the standard "deviation" in FM *audio*
broadcast - a measure of how "wide" the overall signal will be - is +/-
75 kHz from the nominal carrier frequency, for a 15 kHz audio bandwidth.
The relationship between the transmitted signal bandwidth and the original
signal bandwidth in FM is not a simple one, but let's just leave it at the
point of noting that video signals are bandwidth hogs, and TV doesn't
even use regular-old-AM as a result of that. (The luminance signal is
actually sent via "vestigal sideband AM," one step removed from full
suppressed-carrier SSB.)

The audio is FM both to avoid the problems of interference bothering the
sound (just as in FM radio), AND to minimize the effects of the
video portions of the signal possibly interfering with the audio. A TV
channel, though, has relatively lots of room for audio.

Nonsense. The choices of AM and FM within the original analog
standard definitions were made for some very, very good reasons.
Digital television is a completely different beast, and is presently
broadcast using two very different modulation schemes - the
U.S. standard (ATSC) using 8-VSB, while the rest of the world
(mostly) will be using COFDM under the DVB-T standard.

Couldn't FSK [the digital equivalent of FM] be used for luminance [Y]
signal of the digital video?

FSK isn't exactly "the digital equivalent of FM" in the first place, and
the short form answer is no. Digital video is carried in a completely
difference manner, and there isn't exactly a readily-separable
luminance "signal" as such in the transmitted signal, at least not as
something you could identify on a scope as in analog TV - it's all just
bits, and it's all packetized.

Bob M.

The other thing is that the evolution of TV transmission also had to be
compatible with older sets. Hence for example the various ways of
transmitting chrominance alongside luminance. Or stereo sound alongside
mono.

"Bob Myers" wrote in message
...

"Radium" wrote in message
oups.com...

Why not carry the luminance-signal on FM and the audio-signal on AM?

See the previous post; it's basically a matter of the enormous bandwidth
requirements of FM (note that the standard "deviation" in FM *audio*
broadcast - a measure of how "wide" the overall signal will be - is +/-
75 kHz from the nominal carrier frequency, for a 15 kHz audio bandwidth.
The relationship between the transmitted signal bandwidth and the original
signal bandwidth in FM is not a simple one, but let's just leave it at the
point of noting that video signals are bandwidth hogs, and TV doesn't
even use regular-old-AM as a result of that. (The luminance signal is
actually sent via "vestigal sideband AM," one step removed from full
suppressed-carrier SSB.)

The audio is FM both to avoid the problems of interference bothering the
sound (just as in FM radio), AND to minimize the effects of the
video portions of the signal possibly interfering with the audio. A TV
channel, though, has relatively lots of room for audio.

Nonsense. The choices of AM and FM within the original analog
standard definitions were made for some very, very good reasons.
Digital television is a completely different beast, and is presently
broadcast using two very different modulation schemes - the
U.S. standard (ATSC) using 8-VSB, while the rest of the world
(mostly) will be using COFDM under the DVB-T standard.

Couldn't FSK [the digital equivalent of FM] be used for luminance [Y]
signal of the digital video?

FSK isn't exactly "the digital equivalent of FM" in the first place, and
the short form answer is no. Digital video is carried in a completely
difference manner, and there isn't exactly a readily-separable
luminance "signal" as such in the transmitted signal, at least not as
something you could identify on a scope as in analog TV - it's all just
bits, and it's all packetized.

Bob M.

My Velocity Micro ProMagix www.velocitymicro.com
www.velocitymicroblog.com desktop computer has a CD drive and a big
floppy disk drive.(I made sure of the floppy disk drive when I paid
$1,330.00 for my computer) I keep my computer lean and mean, I am not
dumb enough to haul my computer around on the internet in newsgroups and
guestbooks and crap.I have a cheap AM/FM so-called radio here that has a
CD drive on the top of it.I bought the thing at the Sears store about
five years ago.
cuhulin

On Fri, 08 Jun 2007 20:58:04 +0000, Radium wrote:

Why not carry the luminance-signal on FM and the audio-signal on AM?

Because it would be abysmally stupid to try to do so. You'd need about
10 times as much bandwidth if you used FM for the video, and using AM
for the audio would make it susceptible to all manner of noise.

Hope This Helps!
Rich

On Jun 12, 10:57 am, Rich Grise wrote:
On Fri, 08 Jun 2007 20:58:04 +0000, Radium wrote:
Why not carry the luminance-signal on FM and the audio-signal on AM?

Because it would be abysmally stupid to try to do so. You'd need about
10 times as much bandwidth if you used FM for the video, and using AM
for the audio would make it susceptible to all manner of noise.

Isn't the interference on AM video as much of a concern as it would be
on AM audio?

"Radium" wrote in message
oups.com...
On Jun 12, 10:57 am, Rich Grise wrote:
On Fri, 08 Jun 2007 20:58:04 +0000, Radium wrote:
Why not carry the luminance-signal on FM and the audio-signal on AM?

Because it would be abysmally stupid to try to do so. You'd need about
10 times as much bandwidth if you used FM for the video, and using AM
for the audio would make it susceptible to all manner of noise.

Isn't the interference on AM video as much of a concern as it would be
on AM audio?

Nope, not really. The creators of the analog TV standard
did something very clever and yet very simple - in choosing
VSB-AM for the video modulation, they also set it up with
"negative modulation," meaning that the peaks of the
modulated signal correspond to the "blackest" portions of
the video (luminance) waveform - which happen to be the
sync pulses. This means that, in the presence of noise, you
are still very likely to maintain a stable picture; the picture
itself may degrade and get a bit "snowy," but you can still
see it. And it really takes quite a bit of noise to make visible
"snow" show up in the picture. For one thing, video has tons
of redundancy due to the repeated raster-refresh scanning,
so you're very unlikely to see the occasional noise spike.
But also, due to this choice re the modulation, low-level
noise is most likely to show up affecting the brighter parts
of the image, where it is a good deal more difficult to see.
VSB-AM was really the ONLY practical choice for analog
video in the broadcast world. And, as has already been noted,
the situation re the modulation schemes used with "digital"
television are considerably different/more complicated.

Bob M.

Them CD thangys don't last long.If you paid as much as $20.00 for one,
you paid $20.00 too much.
cuhulin