Signal Level Loss in Binuaral Project

Well, the signal level loss was not as bad as I first thought…but the ability to discern AF is not what I was hoping for. With a -40 dBm input signal level, the AF (in headphones) is just barely noticeable. Actually, from -35dBm input and lower, the AF is nearly useable.

I have post the signal level loss with a -3dBm input signal level to show the loss for the RF portion of the receiver to be about -7dBm (from input to product detector).

sig levels - input amp and product detector

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4 Responses to “Signal Level Loss in Binuaral Project”

  1. Mark Dunning Says:

    Hello I made up an LTspice model for your circuit. Given that it is a simplified model not including stray capacitances etc. and I don’t know the inductance of your 4 turn link or effective impedance of the diodes (guessed as 200 Ohms), it still shows that your circuit has a peak response at around 6.2 MHz with a gain at that frequency of 39dB. Gain at 3.55MHz is 15dB. Maybe you have a bad transistor. Also is your local oscillator providing enough drive to the diodes?

    I could send you a JPEG of the simulation if you like.

    Good luck I know how frustrating these things can be.

    73’s Mark VK6WV

    • wb8icn Says:

      Mark, the four-turn link is just four turns wrapped around the inductor (about the size of a half watt resistor). The transistor is working OK. I would be interested in your LTspice model…I run LTspice but never had built a model for this project. Please send a copy to me so I can play with it. My e-mail is wb8icn@gmail.com.

  2. Mark Dunning Says:

    I forgot to include the antenna source resistance. When I assume 50 Ohms, the peak frequency moves to 7MHz and voltage gain changes to 26dB. I had a look back through your posts and note that you only have 300mV out of your oscillator. With silicon diodes I think you will need about 700mV or more to get good mixer conversion.

    73’s Mark VK6WV

    • wb8icn Says:

      You may have something there…I didn’t think about the LO voltage being too low for the 1N4148 diodes. I will have to take a look at that! Thanks Mark!!!

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