Hi ?Mikek,
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The better IMD performance of the Trask circuit, means that it can be used with a larger antenna (one having greater self capacitance) such as a 1m whip.
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The coax transmission line forms a major part of the antenna anyway, so I see little point in having an excessively high value of input impedance, just so that a very small "plate" can be used.
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By using an antenna with a larger value of self capacitance, the issue of the amplifier input shunt capacitance, that otherwise degrades the Signal to Noise performance, is minimised.
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If you use a small plate with a self capacitance value of say 0.5pF, and the amplifier input capacitance is say 2pF (including mounting), then the majority of the input signal is shunted to ground. A 1m whip has a value of self capacitance of around 10 - 15pF, so the amplifier shunt capacitance is much less of an issue.
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Using a larger antenna, also reduces the need for an excessively high value of amplifier input resistance, which also helps reduce problems associated with choking common mode noise induced in the feed line.
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Regards,
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Martin
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On Thu, Mar 13, 2025 at 03:42 PM, Mikek wrote:
I have a question about the Trask push-pull amplifier. Doesn't it have a rather low input impedance to be connected to a probe antenna?
