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Simple Linear Amplitude Modulator with 100% Depth of Modulation

Question asked by Castleview_John on Sep 26, 2014
Latest reply on Sep 26, 2014 by Castleview_John



This is the first time I have used this forum so please excuse any errors in protocol. This really ought to be a trivial question but, in practice, I have found it quite tricky to pin down a simple circuit and components which does what I need at low cost. I need to build an Amplitude Modulator (yes, surprise, they are still used occasionally in new designs) which has good linearity and full double-sideband modulation (i.e. not SSB) with a modulation index of 1. The RF carrier is at about 250 MHz and the modulation is up to 5 kHz


I have tried using a FET modulator, using the non-linearities but have had trouble in quantifying the non-linearities. I have also used a voltage variable attenuator with a linear voltage attenuation vs control voltage which gives reasonable linearity but not perfect (modulation harmonic side-bands about -20dB). So, my question is, can anyone suggest a better method?




John Lillington