[AMPS] Tuned Input Circuit Q
Tue, 9 Oct 2001 12:09:05 -0700
>> You, Rich, and Eimac like pi networks.
>No, I "like" ANY network that provides a low impedance from
>cathode to ground for harmonics of the drive frequency at the
>cathode of the tube. It doesn't matter what that network is, as long
>as it bypasses the cathode for harmonics of the plate current
>waveform and isolates harmonics generated in the tube from the
// By omitting the aforementioned four-letter word that begins with "R",
you might have gotten a less verbose answer.
>> Creative Electronics, RF Power Products, ETO-Alpha. myself, and others like
>> parallel or T networks.
>That doesn't make it a good choice! Just look at IMD in reviews of
>amplifiers (and transmitters), and you will see how little attention
>people pay to building clean systems.
// The FCC's Paragraph D says that splatter in a ham-band should not go
beyond the band edges, so why make ham stuff as clean as possible?
>While parallel networks are often just as good, T networks are
>really a very poor choice. They are a system begging for less-than-
>obtainable IMD or efficiency.
>You have two basic flavors of T networks, and while one type is a
>low-pass and will reduce harmonics appearing back at the exciter
>none of them do a good job of ensuring that cathode doesn't pump
>around with harmonic energy.
>If you have to use three components and a DP switch, you might
>as well do it the most reliable way no matter what you "like". You
>never know what cable length and exciter someone will use.
// In other word's, Ameritron/MFJ's expert sorta likes low-pass
Pi-networks when a Z-transformation is needed -- i.e., the g-g tube's
cathode isn't 50-ohms.
>73, Tom W8JI
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