I can't thank you enough...
The 6 volts is there only when the radio is keyed - I assumed it is there to power the amplified mics regularly used in aviation headsets.
Good, then the battery will last a very long time. Yes, most aircraft mics are either amplified dynamic or electret.
Does knowing the mic sensitivity is -39dB help?
That means your mic puts out 11mVrms. The one I modeled in LTSpice puts out 8mV.
What is "PP" on your schematic?
It is just a node label. In LTSpice, if you "name" a circuit node, then you wil see this name in the waveform plot. Note that I plotted V(DD) as one of the traces in the Turn ON/Turn Off plot to show when the preamp is powered.
I can't find R7 on your schematic - is there supposed to be one?
Nope, that is an artifact of LTSpice. If you add a resistor, and then delete it, LTSpice doesn't reorder the reference designators (unless explicitly told to do so).
Does R2 have to be close to the radio or can it be with the other components.
R2 is the Pull-Up inside the radio. I computed its value from your measurements, and included it only for simulation purposes. It is not part of the circuit you will build.
I assume the following:
1. The coin cell battery holder is indicating 2 x 1.5 battery cells.
2. The V2 at the switched bias source is indicating voltage.
3. U1 is the microphone.
Seems like I have some stuff around here that uses a single 3V coin cell CR2025 sticks in my mind, or maybe CR2035?
V2 is the bias source which exists inside your radio. I turn it on and off to simulate what happens when the radio is keyed.
Yes, U1 is the LTSpice model of an amplified electret mic. The SPL parameter adjusts its simulated sensitivity.
Where would you recommend buying my supplies? I have used Mouser in the past but do not have any loyalty there.
My plan is to find a piece of circuit board, layout the components and join them with trails of solder. Then put the board in a small project box attached close to the radio with female mini jacks for microphone and PTT plugs.
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Mouser or Digikey works for me. For a one-of circuit, I use the double-sided Vector board that has plated-through holes on 0.1" centers, and a surround-ground-plane on one side. This works well by providing a good ground plane and allowing bypassing.
**broken link removed**. You can saw it up with a hacksaw to get several projects on it...