[600MRG] Class E Keying

[Frank Lotito]

I am looking for suggestions on methods to key Class E RF Power Amplifiers for ON / OFF keying, be it at regular CW speeds, or QRSS speeds.  I assume this topic has been discussed in the popular literature, or special interest bulletin boards such at the 600mrg bulletin board.  Improper keying may generate key clicks with its resulting plethora of emissions on either side of the carrier.  This may be a moot point point for the QRSS mode, maybe not.

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I found the 1997 May / June QST 2-Part article by Lau, et. al.  The article presents a drain (B+) keying circuit for the Class E amplifier's 120 VDC drain supply voltage.  For a specified power level a little simple theory gives the relationship that the (approximate) equivalent resistive load on the DC power supply at key down varies as the square of the ratio of drain voltage.  For example, double the design's drain voltage, the equivalent power supply resistance is 4 times that of the lower voltage design. Higher drain voltage designs may have an advantage as in the 1997 QST article's power supply keying design if higher voltage components and semiconductors are available.

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Besides voltage and current concerns, including the problem of obtaining appropriate RF current rated amplifier tuning capacitors, there is the matter of controlling the shape (rise and fall) of the keying waveform.  This is mandatory to minimize key clicks.  Not easily done when the equivalent DC load resistance is only a few ohms.  The Lau design presents a method to shape the rise and fall times of the keyed power supply drain voltage.

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Anything else out there published on keying Class E RF Power Amplifiers (the popular literature, or on an individual's or company's web site?)  I am assuming other designs might be more suitable for the more common 24 VDC systems. Your suggestions are welcome.

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73 Frank Lotito  K3DZ / WH2XHA