Waveform and Vectorscope, Bar signal on a Pedestal

I bought a Leader 5860c Waveform Monitor and 5850c Vectorscope from 1989 last weekend. Setting them up was a challenge.. this is that story.

The Waveform Monitor wasn't as much of a challenge.

Basically it has BNC composite inputs, and I had to get some adapters for my composite cables to convert them over and connect a VCR and a Time Base Corrector to its Input.

The Time Base Corrector could also serve up a 75% Color Bar signal.. which could produce the usual Stair Steps seen in so many old black and white photographs. That also let me find and recognize the dual side by side field 1 and field 2 "humps" and the full frontporch and backporch of each in the center. Along with the IRE (set-up) or Pedestal add signal that picks up the Black level in North American Video signals and "sets it" on a Pedestal just above the sync blanking level.

Even though I "sort of had guidance from a PDF manual" it was for the wrong vintage and kind of vague about terms and very short.

I learned I had to DC restore the signal to keep it from drifting up and down because the signal is by default coupled to the Input as an AC signal about a sync level used to represent the center point of the overall video signal.  The Monitor had a simple button for DC restore and focused the signal on its reference point.

I could then move the signal up and down and left and right with some alignment controls, and rotate the "horizontal level" of the scan using a small tool and a trimmer in the upper left hand of the monitors faceplate.

Scaling was automatic (or "Calibrated") or manual (or "Uncalibrated") when snapped into position the scale on the "graditule" represents the signal in terms of IRE units instead of voltages.

Good since most literature concerns itself with IRE units and not actual "voltage units".

I then put a SignVideo Proc-Amp into the signal path and played with its four controls

1. Black
2. Contrast
3. Saturation
4. Tint

The first two (Black and Contrast) allowed me to move the "floor" or blackest black level of the video signal relative to the "center point" sync refernce level. But that also had a slight effect on the top of the signal represented by the whitest "white" or brightest signal on the screen.

While the video signal on the monitor represents "Luma" or Brightness irrespective of Color.. each color bar has a declining "brightness" on purpose to create the stair steps. Left to right they fall off in perfect step with the bars on a normal video monitor.. but do not represent any color information.

This is exactly so that, the Black control only effects the overall video signal blackest black.

But after that adjusting the Contrast raises and lowers the top of the whitest or "brightest" color bar so that it could be set to IRE 100 .. or perhaps lower. IRE 75 is quoted as common, as are IRE 85 and 95 .. as a hedge against signal sources that may "overdrive" or "blow out" the perceived exposure.. loosing details in the "wash". This is called "clipping" and is to be avoided.

Clipping can also occur at the other end of the scale in the Blackest Black floor.. the goal is to keep tweaking to get most of the signal, most of the time to remain between these extremes.. which can depend upon the exact source used.. but the color bars serve as a first approximation and allow for some sand bagging of the range to protect against "clipping" at either extreme.

So the Waveform monitor is for calibrating or setting the "Black and the White" extremes of the signal using a proc-amp. And setting the Black also adjusts the height of the Pedestal for the Blackest black.. which in North America would be IRE 7.5 high (very important for the Vectorscope).

Next was the Vectorscope.

Its similarly easy to connect a video input signal, but it displays its results in a Polar or radial graph display. Magnitude is by Radius from the center, the other coordinate being an Angular value from a Color Burst reference signal.. not unlike the DC restore recovered "center sync" reference for the Waveform monitor..

And like that DC restoration.. the Vectorscope has to "recover" the Color Burst angle and decode the position of all colors from the signal arrayed in a circular fashion around the graditule or "scale" on the Vectorscope screen.

I made a mistake in seeking to set IRE to 0 for my video signal using a proc-amp to generate the Color bar signals. This caused the Vectorscope to "free wheel" or "spin" like a car drivers steering wheel.. or strobe like the struts on the wheels of a car. I couldn't get it to stop spinning, even using the phase angle adjustment control repreatedly.

Once I did try to switch IRE 7.5 (on) the bowtie pattern snapped on and stayed locked.

Also using a proc-amp as a color bar generator is not ideal.. in tiny fine print, it says you should also connect a video signal to the Input to the proc-amp composite input.. so that a "stable" color burst signal will be included with the color bars generated. This turned out to be true.

While acting as a bar generator the proc-amp cannot be used as a proc-amp, it locks all of its outputs to references.. presumably to act as a "standard" rather than a general purpose (much more expensive tool).

Radius of each bowtie, "spot" represents the relative "color saturation" for that color, as color video  has a familar pallete with the bar pattern, each bar creates one spot in the general vacinity of the graditule regions labled for their color. Angular offset from the color burst frequency determines their "color".

So a second proc-amp can manipulate radius by increasing or reducing "Saturation" and this effects the entire constellation and over all "size" of the Bowtie.

While the same second proc-amp can manipulate "angle" by increaing or reducing "Tint" and this "Turns" whe whole orientation of the Bowtie. The optimum goal being to adjust or tweak out common imperfections that lead to a "cast" or "overall" color problem that effects all colors equally.

Individual colors which require specific tweaks to Saturation or Tint requires the use of a "color generator" or "color corrector" but is independent of the video signal itself.. that would be a manipulation to grant false "color" enhancement and isn't strictly a result of the signal path or current video signal regenerator. That would be more akin to using a "paint brush" to touch up a moving picture as opposed to "fixing" a video signal to be within specifications for broadcast. And is usually something more common in film and telecine to add special effects, or add to a scene to enhance a particular emotion or psychological setting than a strictly physical situation.

So I did notice that the arrangement of the proc-amp controls from Left to Right were not arbitrary, as each from

1. Black
2. Contrast
3. Saturation
4. Tint

tends to progress from that a person would notice the "most" if left uncorrected to the one they would notice the "least".

So in this case Black offsets are noticed first, then Contrast problems, followed by Saturation problems and then Tint problems.

----+-- Black (bottom)
Y - | - ----- waveform monitor
----+-- Contrast (top)
----+-- Saturation (radius)
C - | - ----- vectorscope
----+-- Tint (angle)