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[AMPS] Input Tuned Circuits with Powdered Iron Toroids

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Subject: [AMPS] Input Tuned Circuits with Powdered Iron Toroids
From: (Steve Thompson)
Date: Tue, 9 Feb 1999 07:29:30 +0000
In message <005401be53e1$a0bf6f40$>,
Frank Donovan W3LPL <> writes
>Excellent question!
>A class B amplifier produces many harmonics as it switches from
>conducting to non-conducting, and the input tuned circuit must provide
>an excellent input termination impendance not only at the fundamental
>frequency, but also at the 3rd harmonic and ideally at the 5th harmonic
>as well.   This would not be a problem if it were a Class A amplifier,
>but that's certainly not practical for a high power RF amplifier!
>Even a  short piece of RG-58 between the input tuned circuit and the
>tube socket significantly increases the input termination impedance at
>the harmonic frequencies.  

I'd guess that the phase changes the cable introduces at harmonic
frequencies has a lot to do with it. The loss in a foot of RG58 even at
150MHz is small.


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