On 11 Nov, 08:58, "Stefan Wolfe" wrote:
"Roy Lewallen" wrote in message

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Stefan Wolfe wrote:
"Roy Lewallen" wrote in message
...
Stefan Wolfe wrote:

In a resonant circuit containing R, L, and C, there most definitely is a
time constant. Related to Q, it describes the time taken for the circuit
to respond to a transient. The higher the Q, the longer the time
constant, and the longer it takes the circuit to come to equilibrium
after a step or sinusoid is applied, and to decay after it's removed.
Failure to understand this has resulted in some very poorly designed
audio filters for CW, among other things.

But Roy, I must first clear up that we are talking about apples and
oranges. I was referencing a sinusoidal source of a frequency that is
resonant to the circuit. You are talking about a transient can be treated
as the sum of sinusoids which will not be resonant at the same curcuit. I
was also referring to the antenna as a L-C-R circuit that does have time
constants along its lengths (but I was asking 'where' along the length)
but as a whole system the time contant of the antenna, when fed by a
signal at resonant frequency is zero.
. . .

You've lost me. What is the meaning of a "time constant" in steady state?
What effect does it have? With a single frequency of constant amplitude,
how could you tell whether a circuit, resonant or not, has a "time
constant"? How could you measure it?

The meaning of a time constant is not dependent upon steady state sinusoids
or transient; it is merely a characteristic that dependent upon the
*physical* properties of the components in the circuit.

You know that of course.

Let us say we design a power supply for use in consumer appliances. The
power supply of course has a capacitor across line and neutral for EMI
filtering, along with a bleeder resistor in parallel with this capacitor.
Together, the bleeder resistor and phase/phase capacitor filter have a time
constant. Now the time constant is meaningless with respect to steady state
input voltage (other than wave shaping high f emi components) and with
respect to transients. It is meaningful with respect to safety. If the
consumer pulls out the plug, the bleeder resistor must discharge the phase
to phase cap safely to prevent the consumer from being shocked when touching
the L-N pins. The time constant RC in this case MUST meet certain
specifications, that is it must be less than 0.1sec. That is essentially
required legally (since standard compliance is compulsory). The time
constant exists is chosen for a worse case value, ie that the consumer
unplugs the power supply at the peak of the AC cycle.

Actually, it is the DC discharge characteristic that we care about here.
Transient suppression is not relevant nor is its ability to shape the
incoming sinusoid.- Hide quoted text -

- Show quoted text -

I read thru all and it wasn't until thelast sentence did you state
anything that is relevent. The Dc discharge characteristic
when the terminals are shorted. Discouting the spike at the
beginning the discharge is dependent on the size of the vessel
and restrictions applied by the circuit. The larger the vessel
the sharper the curve with respect to time. This goes for both
the inductance and the capacitance and it is only the losses
which are small take away the perpetual motion.
I suggest you go to google and look up a "tank circuit"
where they will I am sure take you thru the phase changes
that create the pendulum like action.
But then you knew that all along, anything but review the math.
Hot air once again. Why not discuss it with the broadcast engineer
with his long time service at switching on a transmitter every
morning,every day
plus turn the lights out. As Vanna White would say in defence of her
salary status
You have to know the alphabet
Art
Art