On Sat, Sep 4, 2010 at 8:07 PM, Dale Boresz <[email protected]> wrote:
> I used a 3K carbon comp for no reason other than that it was the most > suitable value that came out of the junkbox when I reached in for a 'pinch' > of resistors. :-) It worked fine for the Icom HM-12 microphone that I was > trying to use. > Well, it depends on what the operating current of the electret element is. For a quick and dirty setup, adjust the value of the bias resistor to yield a voltage across the mic element of at least 3V. Most of those electret mic elements are just an open collector or open drain output. The "bias" resistor is really the collector or drain resistor of a common source/emitter amplifier. If the resistor value is too high, you will not have enough voltage drop across the device to get it to operate in its linear region and you will get distortion and low output. OK, I just measured an electret mic element I had sitting on the bench and with a 5V supply a 2K resistor yields a drop across the mic of about 3.5V. The output looks good on a 'scope and sounds good. For this mic the value 220 ohm is probably too low. Anyway, change the value of the resistor in order to get the correct bias on the mic's amplifier and see if that doesn't work just fine, even using the radio-supplied +5V. And it is probably better to make the mic bias resistor too small rather than too large. -- Brian Lloyd, WB6RQN/J79BPL 3191 Western Dr. Cameron Park, CA 95682 [email protected] +1.767.617.1365 (Dominica) +1.931.492.6776 (USA) (+1.931.4.WB6RQN) _______________________________________________ Flexedge mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexedge_flex-radio.biz This is the FlexRadio Systems e-mail Reflector called FlexEdge. It is used for posting topics related to SDR software development and experimentalist who are using beta versions of the software.
