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| To: | [email protected] |
|---|---|
| Subject: | LF: Re: Wilkinson combiner, Phase Shift |
| From: | [email protected] |
| Date: | Tue, 15 Feb 2005 14:01:33 EST |
| Reply-to: | [email protected] |
| Sender: | [email protected] |
|
Dear LF Group, one thing worth considering is the phase shift between the transistors and the antenna input, including all filters and matching circuitry. I have always tried to keep that at 0° or 180°, as this lets the FET's see a series resonant load. This becomes a high impedance in case of antenna detuning or arcing, a safe condition for a class-D voltage source. Actually I have not lost a single FET in spite of several antenna faults (... knocking on wood as I write this ;-). Feeding a tap on the loading coil will introduce a phase shift close to 90°, showing impedance inversion. A Wilkinson combiner also adds in a quarterwave. But of course it is the total electrical length of the output chain at 137kHz that counts. 73 Markus, DF6NM |
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