Maxwell Bridge Discriminator

Discussion in 'General Electronics Chat' started by sjgallagher2, Oct 15, 2013.

  1. sjgallagher2

    Thread Starter Active Member

    Feb 6, 2013
    I'm in the process of learning about radio circuits, and while learning about discriminators I though up an idea! What if you used a Wheatstone Bridge to output the change in voltage with the IF as the input, and a capacitor as the unknown resistance? So that the change in frequency would result in a change in impedance. Looking into the idea I would actually need a Maxwell bridge which is the Wheatstone bridge AC equivalent.

    Do you think this could work? How well do you think it would work? Obviously I just came up with this idea and haven't put much thought into response time and stuff like that. Let me know! Would it be less efficient than a slope detector? I sort of doubt it could be better than the PLL discriminator. Thoughts?
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    In principle I think the idea might work with some caveats concerning matters like output linearity, circuit Q & transient behavior. The attachment shows how one might conceptually do it with a Twin-T bridge arrangement. How it would compare with established methods would be a matter of test & measure.
    However, I think a basic problem with the concept is that the circuit cannot distinguish whether the instantaneous frequency is above or below the center IF, which would probably be its Achilles' Heel.
    Last edited: Oct 18, 2013