Re: Infinite Impedance detectors.
The 'special circumstances,' though, are not mentioned by Sturley! He's an author of pedigree, but it's still appropriate, as good engineers, to challenge and try to understand WHY.
R fervency AC/DC load ratio, with a normal diode detector, it's quite possible to compensate for this by appropriately biasing the diode. The down side is that the bias needed depends on the mean carrier strength, so unless it's derived from a (non-delayed) AVC voltage, it is difficult to get it right. And the load on the final IFT could no longer be represented by an equivalent resistance, meaning that bandwidth would be dependent on signal level, giving hard-to-calculate performance.
With an infinite impedance detector, AC/DC load is not an issue as long as there is a sufficient cathode current drain to allow the cathode capacitor voltage to decay between HF cycles so that it can always follow downward modulation. Upward is not an issue because the valve charges the capacitor with little gulps of current. And load on the preceding IF transformer is infinite anyway so who cares if it's a signal-dependent infinity?
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