Composite video via RF modulator, negative image?

"Dave Plowman (News)" wrote:
In article <493D1D13.D83BA88D@earthlink.net>,
Michael A. Terrell <mike.terrell@earthlink.net> wrote:
"Dave Plowman (News)" wrote:

In article <YOOdnU3VY97Lu6HUnZ2dnUVZ_gednZ2d@earthlink.com>,
Michael A. Terrell <mike.terrell@earthlink.net> wrote:
Composite video has negative sync.

Not as transmitted; tip of sync is peak output power.

That was done so that any 'snow' in a weak picture was white,
instead of black dots.

Quite the reverse, actually.

Really? Show us a valid cite for NTSC Visual modulation that agrees
with you. (Type M) An old term in the US TV industry for sync was
'Blacker than Black'. If the modulation is inverted, any loss of signal
strength causes sync to be affected before the video. I've read the
NTSC documents and arguments that were published at the time the system
was created.

PAL as used in most of Europe uses negative modulation - and one reason
was precisely that interference is less noticeable being black flecks
rather than peak white.
Click to expand...

NTSC uses 'Negative Modulation' as well, and for the reasons I've
stated.

Did you even look at the URL I posted?

http://en.wikipedia.org/wiki/NTSC


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There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.
 
"Dave Plowman (News)" wrote:
In article <gdSdnaKuR60fzqDUnZ2dnUVZ_gGdnZ2d@earthlink.com>,
Michael A. Terrell <mike.terrell@earthlink.net> wrote:

"Dave Plowman (News)" wrote:

In article <493D1D13.D83BA88D@earthlink.net>,
Michael A. Terrell <mike.terrell@earthlink.net> wrote:
"Dave Plowman (News)" wrote:

In article <YOOdnU3VY97Lu6HUnZ2dnUVZ_gednZ2d@earthlink.com>,
Michael A. Terrell <mike.terrell@earthlink.net> wrote:
Composite video has negative sync.

Not as transmitted; tip of sync is peak output power.

That was done so that any 'snow' in a weak picture was white,
instead of black dots.

Quite the reverse, actually.

Really? Show us a valid cite for NTSC Visual modulation that
agrees with you. (Type M) An old term in the US TV industry for
sync was 'Blacker than Black'. If the modulation is inverted, any
loss of signal strength causes sync to be affected before the video.
I've read the NTSC documents and arguments that were published at
the time the system was created.

PAL as used in most of Europe uses negative modulation - and one
reason was precisely that interference is less noticeable being black
flecks rather than peak white.

NTSC uses 'Negative Modulation' as well, and for the reasons I've
stated.

'Snow' due to poor signal tends to be random noise - with the white parts
showing more. And of course with a weak signal interference is more
likely.

Did you even look at the URL I posted?

http://en.wikipedia.org/wiki/NTSC

No. Wiki is in no way a reliable reference source.
Click to expand...

Fine you win. You know everything, and everyone else in the world
are morons.

--
http://improve-usenet.org/index.html

aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm


There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.
 
In article <gdSdnaKuR60fzqDUnZ2dnUVZ_gGdnZ2d@earthlink.com>,
Michael A. Terrell <mike.terrell@earthlink.net> wrote:

"Dave Plowman (News)" wrote:

In article <493D1D13.D83BA88D@earthlink.net>,
Michael A. Terrell <mike.terrell@earthlink.net> wrote:
"Dave Plowman (News)" wrote:

In article <YOOdnU3VY97Lu6HUnZ2dnUVZ_gednZ2d@earthlink.com>,
Michael A. Terrell <mike.terrell@earthlink.net> wrote:
Composite video has negative sync.

Not as transmitted; tip of sync is peak output power.

That was done so that any 'snow' in a weak picture was white,
instead of black dots.

Quite the reverse, actually.

Really? Show us a valid cite for NTSC Visual modulation that
agrees with you. (Type M) An old term in the US TV industry for
sync was 'Blacker than Black'. If the modulation is inverted, any
loss of signal strength causes sync to be affected before the video.
I've read the NTSC documents and arguments that were published at
the time the system was created.

PAL as used in most of Europe uses negative modulation - and one
reason was precisely that interference is less noticeable being black
flecks rather than peak white.
Click to expand...

NTSC uses 'Negative Modulation' as well, and for the reasons I've
stated.
Click to expand...
'Snow' due to poor signal tends to be random noise - with the white parts
showing more. And of course with a weak signal interference is more
likely.

Did you even look at the URL I posted?

http://en.wikipedia.org/wiki/NTSC
Click to expand...
No. Wiki is in no way a reliable reference source.

--
*Arkansas State Motto: Don't Ask, Don't Tell, Don't Laugh.

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
 
In article <493D19C1.71BD227@earthlink.net>,
"Michael A. Terrell" <mike.terrell@earthlink.net> wrote:

isw wrote:

In article <YOOdnU3VY97Lu6HUnZ2dnUVZ_gednZ2d@earthlink.com>,
"Michael A. Terrell" <mike.terrell@earthlink.net> wrote:

isw wrote:

In article <iqpyu52k.fsf@seas.upenn.edu>,
sam@seas.upenn.edu (Samuel M. Goldwasser) wrote:

stratus46@yahoo.com writes:

On Dec 4, 3:42 pm, Berend <berend.van.ber...@gmail.com> wrote:
All,

i've here a Mitsumi MDF8-UE3681 RF modulator that with some help
fromhttp://ask.metafilter.com/56826/now connects an old DVD player
to
an
even older TV set.

But the picture is negative.

The modulator has 4 pins, 3 potmeters, a switch, coax in/out,
and a
cinch connector at the right.

The pins are marked: BS, V, A and B.

A and V is connected to Audio and Video signal.
BS connects to +5v
The a/v shielding and chassis go to GND.

(1 potmeter controls the channel, 1 ferrite core does something
with
audio, and the last is a dragging one that does some w/the
video.
The
switch seems to be for a testpattern with two vertical bars?)

Berend

Are you _certain_ that the modulator requires sync negative? I've
never seen one but it's conceivable to build a modulator that
requires
sync positive. It's not like audio where the absolute phase doesn't
matter. (OK some audio nuts swear they can tell the difference but
most of us can't).

Composite video has negative sync.

Not as transmitted; tip of sync is peak output power.


That was done so that any 'snow' in a weak picture was white, instead
of black dots.

But mostly because sync circuits didn't work very well, and since video
is transmitted as AM (well, the sync frequencies are, anyhow), sync up
gave even a weak signal the best chance of getting a lock.


Really? Sync doesn't work? Then why have we bothered to transmit TV
for over 60 years? In the US, analog TV visual is transmitted as
'Vestigial Sideband', with the sync tips 'Blacker than Black'. That
means it it is at 100% Visual modulation, with full brightness at the
lowest level. US TVs typically used 'keyed AGC', which measures the
received signal levels during the sync pulses. This prevents changes in
average video from affecting the overall system gain. If the visual
modulation is out of spec, the system doesn't work properly.
Click to expand...
Think about how long ago all the specs for RS-170 were laid down. *In
the beginning* things were a bit more difficult, and synchronization was
a bit tricky, what with marginally stable multivibrator oscillators and
all. Using the highest-powered part of the signal for sync made things a
bit easier. "Vestigal sideband" was used instead of true single-sideband
because true SSB is more difficult to receive (since it needs a
synchronous carrier). An interesting benefit of VSB is that for
modulation frequencies near the carrier *where the sync signals are* the
signal is standard double-sideband AM, which *doubles the amplitude of
the detected signal* compared to the single-sideband part; this helps
sync performance. Most of the lower sideband is wiped off on the way to
the antenna, and the characteristics of the filter used must be
carefully specified because there is a complimentary filter in every
receiver.

I was a RF broadcast engineer at three TV stations. I've built CATV
headends, mobile TV production vehicles, and worked with CARS & STL
systems before I became 100% disabled.
Click to expand...
In that case, you may have used some gear that I designed, or helped
design, or managed the design of.

Isaac
 
isw wrote:
In article <493D19C1.71BD227@earthlink.net>,
"Michael A. Terrell" <mike.terrell@earthlink.net> wrote:

Really? Sync doesn't work? Then why have we bothered to transmit TV
for over 60 years? In the US, analog TV visual is transmitted as
'Vestigial Sideband', with the sync tips 'Blacker than Black'. That
means it it is at 100% Visual modulation, with full brightness at the
lowest level. US TVs typically used 'keyed AGC', which measures the
received signal levels during the sync pulses. This prevents changes in
average video from affecting the overall system gain. If the visual
modulation is out of spec, the system doesn't work properly.

Think about how long ago all the specs for RS-170 were laid down. *In
the beginning* things were a bit more difficult, and synchronization was
a bit tricky, what with marginally stable multivibrator oscillators and
all.
Click to expand...

A TV station that I visited in Fairbanks in the early '70s still used
their vacuum tube RCA sync & chroma generator. The master monitor in
the control room was based on the RCA CTC4 TV chassis, and the GE film
chain was tube, as well. The equipment worked, but was very temperature
sensitive. Bad tubes were a problem, as well. Some stations had over
1000 vacuum tubes in the studio & control room. That was one reason TV
stations ran a test pattern for a half hour or more each morning.


Using the highest-powered part of the signal for sync made things a
bit easier. "Vestigal sideband" was used instead of true single-sideband
because true SSB is more difficult to receive (since it needs a
synchronous carrier). An interesting benefit of VSB is that for
modulation frequencies near the carrier *where the sync signals are* the
signal is standard double-sideband AM, which *doubles the amplitude of
the detected signal* compared to the single-sideband part; this helps
sync performance. Most of the lower sideband is wiped off on the way to
the antenna, and the characteristics of the filter used must be
carefully specified because there is a complimentary filter in every
receiver.
Click to expand...

Not to mention the careful alignment of the diplexer to allow the use
of a single antenna.


I was a RF broadcast engineer at three TV stations. I've built CATV
headends, mobile TV production vehicles, and worked with CARS & STL
systems before I became 100% disabled.

In that case, you may have used some gear that I designed, or helped
design, or managed the design of.
Click to expand...

I've worked with a Gates 500 W on Ch 8, a 130 KW Comark UHF on Ch 55,
and a 25 KW RCA TTU-25B that I moved & rebuilt. It had been on Ch 55,
and had to be converted for Ch 58. The RCA was built in 1952.

I've designed a few things for broadcast use, as well. We got a
notice from the FAA & FCC about a change in the laws, regarding tower
lighting. We had 72 hours to let them know if we already had a remote
monitoring system in place, or buy one from an approved equipment list.
I designed and built a system that day, and installed it the next
morning. It used a1024 Hz tone on a spare audio channel in the STL from
our old transmitter site, to the new one. A current transformer
monitored current to the tower lights. The tone was on when the lights
were off, and went off when all the lights were on. A tone decoder at
the other end was mounted in the main console, with a small lamp beside
the master monitor. It was just annoying enough for the operator to
notice, and log the start & stop times each day. I designed and built a
lot of interfaces to connect incompatible hardware, too. The most fun
was transmitting a color station ID at a B&W AFRTS station with no color
equipment, at all. :)


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
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