UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Interesting Armstrong AM detector circuit.

Argus25 · 2nd Dec 2017, 1:35 pm

This was the circuit that gave me the idea for the Supadetector circuit I used in one of the radios I posted in the homebrew section.

There wasn't the power supply available in the radio to do it the H&H way but I considered that dynamically an inductor as a collector load tends to behave as a current source. So I simply converted the IF signal voltage into a current with the transistor and used the inductor to drive the diodes. The diodes are driven into conduction at very low signal voltages, but due to the loading the frequency response and linearity is good.

The H&H circuit of course is the answer to a sensitive and linear wide band RF millivolt meter. To make one I think it merely requires a broadband RF amplifier/buffer & attenuator at the input and this circuit, plus an OP amp and meter bridge.

2nd Dec 2017, 1:35 pm	#32
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: Interesting Armstrong AM detector circuit. This was the circuit that gave me the idea for the Supadetector circuit I used in one of the radios I posted in the homebrew section. There wasn't the power supply available in the radio to do it the H&H way but I considered that dynamically an inductor as a collector load tends to behave as a current source. So I simply converted the IF signal voltage into a current with the transistor and used the inductor to drive the diodes. The diodes are driven into conduction at very low signal voltages, but due to the loading the frequency response and linearity is good. The H&H circuit of course is the answer to a sensitive and linear wide band RF millivolt meter. To make one I think it merely requires a broadband RF amplifier/buffer & attenuator at the input and this circuit, plus an OP amp and meter bridge.