Is this by any chance an exam question?

Roy Lewallen, W7EL

Dave wrote:
What is the resonate frequency of this network, as determined between
the top and bottom of what I have drawn?

I don't know how well the drawing will come out, but it consists of:

100 uH in series with 1000 Ohms.
100 pF in series with 1000 Ohms

The two two networks above are in parallel


i.e.



|
|
!
-----!-----
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L C
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R R
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------------
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Roy Lewallen wrote:
Is this by any chance an exam question?

No, it is not. I was shown it by a lecturer of mine more than 10 years
ago. The result is quite interesting.

On 18 Nov, 06:05, Dave wrote:
Roy Lewallen wrote:
Is this by any chance an exam question?

No, it is not. I was shown it by a lecturer of mine more than 10 years
ago. The result is quite interesting.

Interesting to me is that there is no parallel resistance bypassing
the capacitor inferring a mythical loss less capacitor.
I await developments with interest
Art

Dave wrote:
Roy Lewallen wrote:
Is this by any chance an exam question?

No, it is not. I was shown it by a lecturer of mine more than 10 years
ago. The result is quite interesting.

With the given values, it's a constant-impedance network. I've used one
many times in time domain circuit designs. Its impedance is a constant
real value of 1000 ohms at all frequencies. Since "resonance" implies a
single frequency (at which the reactance is zero), this circuit isn't
resonant at any frequency. The circuit is often used in time domain
applications (e.g., oscilloscopes) where it's sometimes necessary to
provide a constant impedance load but you're stuck with a capacitive
device input impedance. In that situation, the C is the input C of the
device. However, the transfer function isn't flat with frequency-- you
end up with a single pole lowpass rolloff, dictated by the R and C values.

For anyone who cares about such matters, "resonate" is a verb,
"resonant" is the adjective, and "resonance" the noun. A resonant
circuit resonates at resonance.

Roy Lewallen, W7EL

In message , Roy Lewallen
writes
Dave wrote:
Roy Lewallen wrote:
Is this by any chance an exam question?
No, it is not. I was shown it by a lecturer of mine more than 10
years ago. The result is quite interesting.

With the given values, it's a constant-impedance network. I've used one
many times in time domain circuit designs. Its impedance is a constant
real value of 1000 ohms at all frequencies. Since "resonance" implies a
single frequency (at which the reactance is zero), this circuit isn't
resonant at any frequency. The circuit is often used in time domain
applications (e.g., oscilloscopes) where it's sometimes necessary to
provide a constant impedance load but you're stuck with a capacitive
device input impedance. In that situation, the C is the input C of the
device. However, the transfer function isn't flat with frequency-- you
end up with a single pole lowpass rolloff, dictated by the R and C values.

For anyone who cares about such matters, "resonate" is a verb,
"resonant" is the adjective, and "resonance" the noun. A resonant
circuit resonates at resonance.


I think that the principle of this circuit is similar to the
constant-impedance equaliser - such as used to compensate for the loss
of a length of coaxial cable over a wide range of frequencies (very
common in the cable TV world). This is frequency-selective in that it
has essentially zero loss at a pre-determined 'top' frequency (say
870MHz), with progressively increasing loss at lower frequencies (the
inverse of the cable loss). As it has a constant (75 ohm) input/output
impedance, it is therefore resonant at all frequencies from 0 to 870MHz.
--
Ian

Ian Jackson wrote:

I think that the principle of this circuit is similar to the
constant-impedance equaliser - such as used to compensate for the loss
of a length of coaxial cable over a wide range of frequencies (very
common in the cable TV world). This is frequency-selective in that it
has essentially zero loss at a pre-determined 'top' frequency (say
870MHz), with progressively increasing loss at lower frequencies (the
inverse of the cable loss). As it has a constant (75 ohm) input/output
impedance, it is therefore resonant at all frequencies from 0 to 870MHz.

I've designed a couple of coax loss compensators, for very high speed
digital oscilloscope delay lines. They had to preserve the fidelity of a
high speed step to within a very few percent, which amounted to very
precise compensation of both the frequency and phase response.
Bandwidths were about 2 and 9 GHz. The dominant loss mechanism in high
quality coax over those frequency ranges is due to conductor skin effect
which is proportional to the square root of frequency, so no single
network will do the compensation. I used a number of bridged tee
networks to do the job, each correcting a different part of the time
response (equivalent to different frequency ranges), in some cases
transforming them to other topologies to accommodate unavoidable stray
impedances due to components and layout. The circuits were used in the
Tektronix 11802 and TDS820 oscilloscopes.

Roy Lewallen, W7EL