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kalee20 · 5th Dec 2017, 6:17 pm

I'd not thought of that! And it would be even worse if there was an emitter capacitor to hold-up the emitter voltage.

1V RMS carrier input... that's 1.4V peak... If 100% modulated then at the modulation peaks the voltage will be double, so that's 2.8V, which the emitter capacitor would charge up to... then at the modulation peak but half an RF cycle later the base would be at -2.8V, thus 5.6V reverse Vbe with only 1V RMS carrier in! (yes I know I neglected the forward Vbe drop, but this is only a crude estimate...)

So yes, not much dynamic range for a standard silicon planar transistor.

5th Dec 2017, 6:17 pm	#40
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,077	Re: Infinite Impedance detectors. I'd not thought of that! And it would be even worse if there was an emitter capacitor to hold-up the emitter voltage. 1V RMS carrier input... that's 1.4V peak... If 100% modulated then at the modulation peaks the voltage will be double, so that's 2.8V, which the emitter capacitor would charge up to... then at the modulation peak but half an RF cycle later the base would be at -2.8V, thus 5.6V reverse Vbe with only 1V RMS carrier in! (yes I know I neglected the forward Vbe drop, but this is only a crude estimate...) So yes, not much dynamic range for a standard silicon planar transistor.