This is the main page for my team-related homework for the
Napa Valley College's
Broadcast Television Engineering Technology
Operator Electrocution Protection Provided by the CCU
Here is a short paper on how CCUs provide electrocution protection to operators
who may have to detach a triax cable which, among other uses, is used to supply
240 VAC to power the camera.
Bipolar Junction Transistor Amplifier Configurations
Here is the latest set of notes on bipolar junction transistor amplifier configurations.
Video Signal Clamping
Here is the latest set of notes on video signal clamping.
What Effect does a Circuit-coupling Capacitor have upon the 6-MHz NTSC Video Signal?
Capacitors are often used to separate the output stage of one circuit from the input stage
of the next circuit.
This is done to block DC flow, since the DC voltage at an output stage may be significantly
different from the voltage at an input stage, and the signal of interest to the system is AC.
What effects or problems would be introduced upon the NTSC video signal
(comprising luminance, chrominance, and audio) by these capacitors?
Here are my guesses:
- Since the bandwidth is wide (6 MHz), the capacitive reactance of a capacitor
will differ within this band.
This may be significant.
This means that higher frequency portions within the bandwidth will pass through
a capacitor with less reactance than lower frequency portions.
Portions of the signal could be differentially attenuated as a result.
- Color on video is modulated onto the color subcarrier at 3.579545 MHz using
the QAM (quadrature amplitude modulation) method.
Phase is important in color information; the phase of a color signal
with respect to the burst reference determines the color of the signal.
Capacitors result in current leading voltage by 90 degrees.
Does this cause a shift in phase of the color subcarrier and the
information modulated onto it?
If so, this would result in a later stage of television system incorrectly representing
the color of a video signal.
This might not be a problem since the entire signal would be shifted, including the burst color reference.
- Giving up on guessing, and searching the internet for information on this, I found
a web site that discusses AC-coupled and DC-coupled circuits.
AC-coupled circuits use a capacitor in series between stages;
this site reports that this causes distortion of the video signal.
It also talked about the issue of the capacitor needing to be a large value
so that it would not block the frame rate frequency (30 Hz or 25 Hz).
A large capacitor takes up space and adds to the cost of the product.
This company's system uses two capacitors in parallel to avoid the cost of a single large capacitor.
- Another page by the same company above discusses
the effect of AC-coupled circuits upon video signals
in more detail.
The page discusses how biasing the input of a stage after the signal has passed through
a series capacitor from the output of a previous stage is difficult because much of the video signal
(like luminance) has a complex waveform.
The article then describes how clamping is used within video circuits to resolve this issue.
It also explains that while chroma's lowest frequency is about 2 MHz, the lowest frequency
within luminance, composite video, and RGB video is the frame rate.
According to the article, using a capacitor with insufficient capacity results in distortions
called line droop and field tilt,
causing the image to get darker on the right than on the left
and to get darker on the bottom than the top.
Crystals and Crystal Filters
Here is the latest set of notes on crystals and crystal filters.
Here is the latest paper on resonance.
RL Time Constant
Here is the latest paper on RL time constant in various formats.
RC Time Constant
Here is the latest paper on RC time constant in various formats.
Vectors, Phasors, Complex Numbers
Here are the latest copies of papers on vectors, phasors, and complex numbers in various formats.