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Visual "clipping"?

J

Jerry Avins

Jan 1, 1970
0
Richard said:
...

But: 1) it *is* a linear system and maximum amplitude still stresses
the amplifiers, etc. and 2) maximum amplitude also stresses the
downstream circuit: waveguide, switches, impedance matching and
phasing circuits, and even antennas. Remembering that the visual
signal is AM. OTOH, the aural signal is FM and should be running
at a constant amplitude/power regardless of modulation (or not).

Do you mean that the waveguide or transmission cable is the weak link in
the transmitter? Somehow, I don't think so. Maximum output indeed
stresses the system, but somewhat less than maximum stresses the output
stage more. The math is pretty simple.

Jerry
 
M

Mr.T

Jan 1, 1970
0
A common misconception for a simple overloading problem.
Actually, when you clip a sine wave you get a square wave.

Actually you get a clipped sine wave, it will not have the straight sides of
a square wave.
Only if the clipping is astronomically severe will it approach a true square
wave.
It only has odd harmonics

True for a square wave, not quite so true for a clipped sine wave.
Clipping is a way for an amplifier to continue to provide increasing amounts
of power to a speaker as the input increases, even though the amplifier has
reached its voltage and/or current limits on the peaks. It is usually
simply the additional power that breaks the drivers.

Agreed.

MrT.
 
A

Al in Dallas

Jan 1, 1970
0
snip

More Trolling.

Exactly where did he say prolonged black can damage a monitor/screen

But is it trolling or is Radium just inattentive to details because
he's too excited about the conversation?
 
A

Al in Dallas

Jan 1, 1970
0

I've been an engineer for 25 years. Many of my colleagues have lacked
much in the way of a normal sense of humor. Non-engineers seem to rate
us as second place for being strange, overly literal, and humorless.
Accountants take first place.

The engineering student went home for vacation to his rural town. When
relatives insisted on an example of what he'd learned, he said
"pi-R-squared." Someone replied, "Gah, you got that wrong; cornbread
are square; pie are round!"
 
M

Michael A. Terrell

Jan 1, 1970
0
Al said:
I've been an engineer for 25 years. Many of my colleagues have lacked
much in the way of a normal sense of humor. Non-engineers seem to rate
us as second place for being strange, overly literal, and humorless.
Accountants take first place.


Al, the uninformed just don't get our humor, even if we try to
explain it to them. I was an engineer at an AFRTS TV station at Ft
Greely in the '70s. I had a problem with a couple of the talking heads
on our live newscast. They wouldn't stay in their seats, or even on set
during actualities, so I rewired their off air monitor. The next
newscast they got up and were shadow boxing in front of the news desk
when the sound went dead, and they thought that they were on air, in
their dress uniform jackets, and underwear. (No air conditioning at the
station). Needless to say, they freaked out! The next time they got
out of line was a Saturday noon newscast, where a fishing program from a
station in Fairbanks was on their off air monitors. :)

My best pranks at the station? One of the staff was a drunk and he
was always bragging that he was too smart to get caught. The late night
DJ had relatives that worked at a NOAA weather station nearby, and a lot
of nights they would bring him supper. They had brought the bottle with
the food, and it might have had a quarter of a cup. I was going to make
a bank out of the bottle, but I couldn't carry it back to the barracks
that night, so I hid the empty wine bottle inside the console, behind a
rack mount CCU power supply. The station manager found it, and raised
bloody hell. The guy drank so much that he truly couldn't remember if
it was his bottle, so I just stood back and enjoyed the floor show.
before it was over, he admitted to drinking on duty, and apologized for
leaving the empty bottle. The manager pulled him from engineering
rotation, then put him on day shift in the film library.

Another time we had a general from the Pentagon visiting the base. He
called the station and didn't identify himself. He ordered me to run
something else, because he had seen the movie the week before, in DC. I
replied, Sorry sir, but I haven't seen it, and hung up. He called right
back, and started yelling that he was a general, and that if I didn't
obey his order, he was calling my commanding general. I laughed and
said, "Tell him that Michael said 'Hello'." He snarled "What the hell
does that mean?" I laughed and told him, "My General will explain it to
you, if you're stupid enough to call him". He proceeded to brag about
all his friends in DC, so I reminded him that he wasn't in DC, but at
the US Army cold weather test site, 105 miles from the nearest real
town. Then I told him all the places that I had friends. He grumbled,
"One damn phone call and I'm out of here!" I asked him how he would
find a working outside phone line, or mail a letter if word spread that
he was trying to disrupt our only entertainment. Then I twisted the
knife a little more and said, In fact, if you piss off the wrong people,
they will lose your orders, and report you as AWOL and last seen heading
for the Bering Straits, and Russia. Your Pentagon friends wouldn't help
you if they think you're a commie, will they? He never called back.
Was it something I said? ;-)



My all time favorite was running a station ID in color, on a B&W only
'60 RCA and Gates plant. The Base Information Officer was telling
everyone that the station could not be converted to color. I don't know
about you, but I have never let the 'unwashed' tell me what I CAN'T do.
I borrowed a Heathkit color bar generator, made a custom 35 mm ID slide
with parts from the slide repair kit, and dry transfer lettering from
the leftover bin in the newspaper office. I used the very basic video
keyer in the '60 vintage RCA video switcher to invert the video from the
film chain to display:
AFRTS
CH8

in bold colors on a black background. Boy, did the excrement hit the
rotary oscillator! The shit hit the fan, too! ;-)

Five seconds later, the control room's private phone line was
ringing. The base information officer was screaming, "Soldier, you've
just made a fool of me!" I replied, "But Sir!, You've always bragged of
being a self made man!". He never spoke to me again, or bothered
anything in the radio or TV station. I know he called my commanding
general, and was told to leave me alone, and stay out of the transmitter
and control room, for his own good. :)

I had an ongoing problem with the base power plant. They
intentionally caused brownouts, and used us as a power dump. I was less
than five minutes into the first of three reels of kinescope of the '74
world series when my line voltage dropped from 120 VAC to 25 VAC, shot
up over 210 VAC (the upper limit of the AC line meter), and was tripping
circuit breakers all over the complex. That was the final straw! After
I picked up all the pieces of shredded film, I had one of the DJs cut a
custom 30 second cart with "AFRTS CH8 will return to the air as soon as
the AC power problems are resolved. If you have any questions call:
XXX-XXXX" The phone number was an unlisted line into the power plat
manager's office. He got several *hundred* phone calls, and I never saw
the line voltage vary more than 5 volts after that. ;-)

In spite of all this, I had turned a station that could barely sign
on each day, into one that ran over seven months without an on air
failure. I made E4 at around 20 months and received a letter of
commendation from my commanding General.

A few weeks after I left that station, the two chief engineers from
the Fairbanks TV stations paid a visit to "Help out the poor dumb GIs at
that crappy little military TV station" They were pissed off at how
well the station was running, and admitted to the other engineer that it
was in better shape that either of their stations. My friend Neeley "The
Hoop" asked them, "Do you remember the soldier that you refused to give
the nickel tour of your stations"? He did all the work.

--
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
 
M

Michael A. Terrell

Jan 1, 1970
0
Jerry said:
Do you mean that the waveguide or transmission cable is the weak link in
the transmitter? Somehow, I don't think so. Maximum output indeed
stresses the system, but somewhat less than maximum stresses the output
stage more. The math is pretty simple.


No, unless the waveguide is damaged. A tower worker found a hairline
crack in our waveguide when he leaned against the corner, and received a
six inch long RF burn. We had a slow nitrogen leak we couldn't find,
but he did. The crack was invisible, but it cause the pressure to
change, with temperature. There was approx. 195 KW of UHF RF in that
rectangular waveguide, all 1800 feet of it. If the pressure was low, it
changed the dielectric characteristics, which caused sync clipping.


--
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
 
M

Matt Ion

Jan 1, 1970
0
Michael said:
Five seconds later, the control room's private phone line was
ringing. The base information officer was screaming, "Soldier, you've
just made a fool of me!" I replied, "But Sir!, You've always bragged of
being a self made man!". He never spoke to me again, or bothered
anything in the radio or TV station.

Now THAT is CLASSIC! :)
 
J

Jerry Avins

Jan 1, 1970
0
Michael said:
No, unless the waveguide is damaged. A tower worker found a hairline
crack in our waveguide when he leaned against the corner, and received a
six inch long RF burn. We had a slow nitrogen leak we couldn't find,
but he did. The crack was invisible, but it cause the pressure to
change, with temperature. There was approx. 195 KW of UHF RF in that
rectangular waveguide, all 1800 feet of it. If the pressure was low, it
changed the dielectric characteristics, which caused sync clipping.

Just curious: how did you fix it?

Jerry
 
M

Michael A. Terrell

Jan 1, 1970
0
Matt said:
Now THAT is CLASSIC! :)


Its too bad that I STILL can't tell the really good stories. :(

--
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
 
M

Michael A. Terrell

Jan 1, 1970
0
Jerry said:
Just curious: how did you fix it?


"I" didn't. The defect was about 1000 feet above ground, and was
probably damaged when they worked on the FM curtain antenna for five of
the 'Orlando' FM radio stations.

The waveguide was custom made and under warranty, so the OEM had to
build and ship a replacement. The tower crew was called to replace it,
then the defective brass was shipped back for their inspection, and to
be scrapped. The same guy was on the second crew and had no trouble
remembering the spot where he got a second degree burn on his ass, so it
didn't take very long to swap out. Remove all the flange bolts, free up
the hanger hardware and slide it out. CAREFUlLY slip the new piece into
place and replace all the brass bolds. They did it one Sunday night
between midnight and 6:00 AM when the transmitter was off line for
weekly maintenance. The Chief engineer was there that night, instead of
me. The next weekend it was time to flush the coolant, and replace it
so four of us worked our asses off to drain the system, clean it, flush
it twice, then refill it with distilled water and antifreeze. It took
almost seven hours so we were late signing on, Monday morning. The rest
of the week it was in operation 24/7.


--
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
 
M

Matt Ion

Jan 1, 1970
0
Duct tape, of course :)
then the defective brass was shipped back for their inspection,

Would that defective brass be the aforementioned "self-made" officer?
Hehehehe!
 
D

dmaster

Jan 1, 1970
0
The similarity is probably in the realm of "loss of information". The
difference is that the speaker system you are probably thinking about
receives both frequency (which sound) and power from an external
source: your amplifier. In video systems, no "power" is delivered to
the display device; only information that defines the color and
brightness.
What does this look like on a screen?

Simple: at the white end, near whites all become white. At the black
end, near blacks all become black. The result is loss of detail.
Near white areas look like a single patch of white with no detail.
Near black areas look like a single patch of black with no detail.

No. While long term display of the *same* image can damage some
monitor technologies, there is no picture/color you can display that
can damage the display device.
No. Prolonged blacks can damage television transmitters, however (video
is inverted for transmission, so black requires full power from the
transmitter).

Prolonged black can damage a monitor/screen? That's weird. White is
analogous to the loudest sound a loudspeaker can playback. Black is
analogous to a loudspeaker not being feed any signal.

When the power-supply of the monitor/screen is turned off, the monitor/
screen is black because it not receiving any voltage.

I would think that extremely-bright white would damage the screen
because the brightest white results from the highest voltage applied
to the Reds, Greens, and Blues [equal intensities of R, G, & B -- if
combined -- appear white to our eyes when emitted by an electronic
monitor] in a particular area of the monitor/screen. If the voltage
exceeds this for prolonged periods of time, that region of the screen
will burn out, much like forcing an extremely-high voltage audio
signal into a speaker will cause the speaker to short-circuit and the
diaphragm to pop and/or melt. Many instructions manual for speakers
give direction not to reach or go above the clipping point and
clipping damages the speakers. Wouldn't something similar happen to a
monitor/screen [whether it's a CRT, plasma, or LCD] if it was forced
to display light-intensities beyond its limits?

No, because the "amplifier" is integral to the display and won't
produce something which would damage the display device. (You need to
learn something about display technologies.) Let's just look at LCDs
(each technology is unique so you'll need to read about the others).
An LCD display can be thought of a large array of red, green, and blue
doors in front of a light bulb. The light bulb is always on. The
video signal tells the display which of the red/green/blue doors to
open at each location on the screen. If all three doors are open, the
white light from the bulb is visible. If only the red door is
*closed*, the light is colored red. If all three doors are closed,
the light is blocked and the location looks black. There is no such
thing as "too much light" because the information source doesn't
control the light bulb, only the doors.

Dan (Woj...)
 
M

Michael A. Terrell

Jan 1, 1970
0
Matt said:
Duct tape, of course :)


You never use duct tape on a tower. It holds moisture, which leads
to rust, then to a tower collapse.

Would that defective brass be the aforementioned "self-made" officer?
Hehehehe!


No, he was in Alaska, the bad waveguide was near Daytona Beach,
Florida


--
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
 
J

Jerry Avins

Jan 1, 1970
0
Michael said:
You never use duct tape on a tower. It holds moisture, which leads
to rust, then to a tower collapse.

I once patched a waveguide with an acetylene torch, borax, and a piece
of low-melting (silver-bearing) brass. I'm sure it played havoc with the
internal silver plating, but that's life, one does what one can. Of
course, X-band guide is easier to heat locally that TV guide.

Jerry
 
M

Michael A. Terrell

Jan 1, 1970
0
Jerry said:
I once patched a waveguide with an acetylene torch, borax, and a piece
of low-melting (silver-bearing) brass. I'm sure it played havoc with the
internal silver plating, but that's life, one does what one can. Of
course, X-band guide is easier to heat locally that TV guide.


This was at least 1/4" brass plate, so the torch would have likely
burnt a hole before brazing properly. If the weld isn't clean on the
inside, it will turn a lot of RF into heat. That is probably what
cracked the weld in the first place. A tiny bit of flux, or oxide that
didn't burn away during the machine welding process. Imagine something
stuck into a 195 KW microwave oven. :)


--
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
 
J

Jerry Avins

Jan 1, 1970
0
Michael said:
This was at least 1/4" brass plate, so the torch would have likely
burnt a hole before brazing properly. If the weld isn't clean on the
inside, it will turn a lot of RF into heat. That is probably what
cracked the weld in the first place. A tiny bit of flux, or oxide that
didn't burn away during the machine welding process. Imagine something
stuck into a 195 KW microwave oven. :)

You don't burn holes before a lower-melting brass liquefies. I wrote
"acetylene" -- Prestolite -- not oxycetylene. Brass is what is called
"hot short", i.e., more brittle hot than cold. The wetting ability of
some brazing rod is amazing. I have seen it wick through and along
cracks that weren't noticed on casual inspection. (But I wouldn't depend
on it.)

Apropos nothing: There are some pretty marvelous alloys around.
Cerrosafe melts at a low enough temperature (165F) so that you can, with
some discomfort, hold a puddle in the palm of your hand. It shrinks upon
solidifying to facilitate removal from the mold, then expands at room
temperature to exactly the size of the mold it froze in. Gunsmiths use
it to gauge size and roundness of cartridge chambers. Ain't technology
grand?

Jerry
 
M

Michael A. Terrell

Jan 1, 1970
0
Jerry said:
You don't burn holes before a lower-melting brass liquefies. I wrote
"acetylene" -- Prestolite -- not oxycetylene. Brass is what is called
"hot short", i.e., more brittle hot than cold. The wetting ability of
some brazing rod is amazing. I have seen it wick through and along
cracks that weren't noticed on casual inspection. (But I wouldn't depend
on it.)


How do you propose to control what flows into the waveguide? I have
never heard of anyone even attempting to repair high power waveguide in
the field. Also, since it is pressurized, what is to stop you from
making the crack worse?
Apropos nothing: There are some pretty marvelous alloys around.
Cerrosafe melts at a low enough temperature (165F) so that you can, with
some discomfort, hold a puddle in the palm of your hand. It shrinks upon
solidifying to facilitate removal from the mold, then expands at room
temperature to exactly the size of the mold it froze in. Gunsmiths use
it to gauge size and roundness of cartridge chambers. Ain't technology
grand?


Are YOU willing to make repairs over 1000 feet in the air, while
hanging from a harness? There are some pretty nasty winds at that
level, so close to the ocean. Some people don't try to get by with half
assed repairs. This is a straight vertical run, other than the
flanges. As I stated earlier, the waveguide was under warranty and the
tower lease included all required repairs. IOW, WE were not allowed to
even attempt a repair, even though the tower was on the TV station's
property.

--
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
 
G

Grouchy

Jan 1, 1970
0
Hi:

Clipping in an audio signal results when an audio device receives a
signal that is too loud. The audio signal distorts into square-waves
because the "tops" of the signal are flattened. The device cannot
handle power levels over a certain level. When this level is exceeded,
clipping occurs. Clipping is usually harsher in digital devices than
in analog devices. Analog clipping tends to be fuzzy and soft compared
to digital clipping.

What is the visual-equivalent of "clipping"? Is there a difference
between analog and digital in terms of visual-clipping? If so, what is
the difference?

Auditory-clipping can damage speakers. Can visual-"clipping" damage
monitors?

Thanks,

Radium

Sir,

I suggest you begin here regarding video 'clipping'... it's the NTSC
site and has links to more in depth sites if it doesn't answer your
question:

http://www.ntsc-tv.com/index.html

In a manner of speaking, digital compression methods are all sort of
"clipping" in a certain sense of the term... Maybe you're thinking of
'clamping' circuits, rather than clipping networks?

Best,

Grouchy
 
A

Arny Krueger

Jan 1, 1970
0
Are YOU willing to make repairs over 1000 feet in the air, while
hanging from a harness?

I always liked the time I spent in a climbing harness attached to something
firm. It was the unclipping to take up some new position or the time that
had to be spent high unclipped that bothered me.

I've never worked on towers higher than about 80 feet, but as they say, its
the first 40 feet that kills you. :-(

In fact a tech at another battery in our batallion did fall off a tower
during my tour in Fla. and suffered the expected fate. :-(

The worst thing that ever happened to me was a mild head injury due loosing
my balance and ending up too close to a slewing radar. Towers in Homestead
were covered with about an inch of water due to condensation from the
everglades and the ocean, in the morning. I was approaching the safety
switch at the time!
There are some pretty nasty winds at that
level, so close to the ocean. Some people don't try to get by with half
assed repairs. This is a straight vertical run, other than the
flanges. As I stated earlier, the waveguide was under warranty and the
tower lease included all required repairs. IOW, WE were not allowed to
even attempt a repair, even though the tower was on the TV station's
property.

The anecdote reveals the context with the mention of X-band. It was likely a
military radar, and the brazing was probably done with the piece of
waveguide removed from the radar and sitting on a bench.

The part about the story that I don't get is that we had ionization
detectors on our waveguides, and they always seemed to shut things down
before the situation got too far out of hand.
 
Are YOU willing to make repairs over 1000 feet in the air, while

I've never worked on towers higher than about 80 feet, but as they say, its
the first 40 feet that kills you. :-(

Actually, no, it's the last couple of inches.

I doubt that many people ever died of falling. They
pretty much all died of the sudden stop at the end.
The worst thing that ever happened to me was a mild
head injury due loosing my balance and ending up too
close to a slewing radar.

Suggesting ... ?
 
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