Message 19727 in TECH.WW
From: G8MNY
Date: Sat, 28 Mar 26 09:46:00 Z
Newsgroups: TECH.WW
Subject: Tuned Circuit Scope Demo
Message-ID: <55650_GB7CIP>
Path: N2NOV|VE2PKT|GB7BED|GB7YEW|GB7CIP
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R:260328/0946Z 3014@VE2PKT.#TRV.QC.CAN.NOAM LinBPQ6.0.25
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R:260328/0946Z @:GB7CIP.#32.GBR.EURO #:55650 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (New Jan 10)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Recently I used an oscilloscope to demonstrate what is going on in a tuned
circuit for an advanced Ham class.
My 100MHz scope can do 4 traces using the 2 triggers as inputs, so I looked at
using all 4 traces.
I used 10:1 scope probes for the larger Input & Output signals, & 1:1 probes on
the smaller current sampling voltages. The Rs short is used when you sweep the
frequency so you can better see the L & C currents levels varying. With Rs in
circuit the selectivity can be shown & also heard on the LS.
SCOPE DISPLAY
Frequency Below Res Freq @ Resonance Frequency Above Res
Points to notice:
Ic = Il at resonance, & it is why the circuit exhibit high Z at resonance.
The Output is not only largest @ resonance but also in phase with the Input.
WHAT IS Q
The meaning of Q can also be discussed & measured with this arrangement.
Fc
OTHER WAVEFORMS
The filtering effect on Triangle & Square waves can be shown, & notice the high
pulse shaped currents in the capacitor! This means that capacitors need low
inductance leads (very short) if they are to filter out harmonics!
The harmonics present in a Square wave can be demonstrated too by making the
frequency 1/2, 1/3, 1/4 & 1/5 of 536Hz resonance! Sine wave harmonic Outputs @
536Hz will be seen on the odd harmonics only.
_ Level
1 3 5 7 9 11 13 15 17 19 21 23 25 27
Harmonic
See my Tech buls on "Scope RF Trick", "SSB Demo circuit", & "Oscilloscopes" &
"Spectrum Harmonic Demo circuit".
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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