Re: Trouble With Alternate Audio Inputs (BITX40 Module)
|
Are you using screened audio leads or simply two wires? If you are not using screened wired between the source you are using and the mic input you are courting all sorts of problems. Regards Lawrence
On Mon, Mar 27, 2017 at 4:02 AM, <bruce@...> wrote: Hi: I'm trying to feed some different audio sources into the BITX40 mic input.? The stage that I'm feeding the BITX40 has an isolation transformer (pictured below) and some other components that provide RFI suppression.? The stage also has a capacitor to block the DC bias that is provided by the BITX40 (I have not cut out the bias resistor in the radio). ? For some reason when I key the rig there is an oscillation that puts the rig into full RF output.? When I switch back to the supplied electret mic everything is fine. ? I am testing on battery power to rule out any supply issues and I have also shorted the input side of the isolation transformer to rule out any problems with earlier audio stages. ? Obviously, my issue is related to the differences between the supplied electret capsule and the audio stage that I am using to drive the radio.? I'm not very experienced with audio circuit design. Two questions: 1. Does anyone have the actual data-sheet for the microphone capsule that is shipped with the BITX40 module?? It would be good to have some details on impedances, etc. 2. Has anyone come up with pre-amp/audio interface that works well with the BITX40? This is what I have right now: 
Thanks and 73s, Bruce KC1FSZ
|
