Re: Microphone appears dead

Bob Lunsford <nocrud222@...>


10) With the V6 connected to a dummy load, try transmitting while monitoring with an existing ham rig, if available, tuned to same frequency and in same mode. If volume is not turned down, you will probably hear a loud squawk from the monitoring receiver due to audio/free air feedback. Turn down monitoring receiver volume and try whispering into the microphone to see if transmitted signal is being received. The receiver can be disconnected from the antenna or it's antenna connector can be shorted out and the V6 can still be received if they are near each other.

I did this with my V6 and verified that there was modulation and that the signal was being received. However, a QRP watt meter between the V6 and dummy load will be required to know the power output. If you whistle into the mic, the tone should be the same on the monitoring receiver or, if not, it will indicate the difference in tuning/calibration on the V6 AND the monitoring receiver. If they are both on frequency, there should be no variation (beat signal) between the V6 transmitter and the receiver.

Note also that the SSB output will be lower than the actual peak power unless the watt meter is designed to read peak power. OR, if your dummy load has the feature, you can measure the voltage across the dummy load resistor on transmit and do the math to know the average/effective power delivered to the dummy load.

Hope that in here somewhere is something you can use and not have to set up a microphone test circuit. By the way, an audio signal tracer, if available, is a cheap and dirty way to see if the mic is working (as long as  bias voltage is applied to the mic) but it will only identify the existence of an audio signal. It will not tell you how strong the signal is (unless it's a top-of-the-line signal tracer) and will not tell you anything about signal quality or voice characteristics.

As indicated in the previous message by Arv, there are many ways to see if the mic is working. Let us know what you find.

By the way, I took the eletret microphone element from an non-working Family Radio el cheapo transceiver and I know it was working until the mode switch went belly-up. Therefore, you can try other elements but remember that all eletret elements are not the same in size or electrical design.

Bob — KK5R

On Saturday, June 27, 2020, 3:29:40 PM EDT, Arv Evans <arvid.evans@...> wrote:

Several ways to test your electret microphone capsule.

1)  make up a simple adapter so you can connect its output 
to the audio  input of the receive side of your transceiver.

2)  Wire up an LM386 as a simple audio amplifier and connect 
the microphone output to this amplifier input.

3)  Wire up a microphone bias circuit and measure the mike 
output with an oscilloscope.  Level should be around 45 to 50 

4) try your microphone on some other rig.

5) Wire up a microphone bias circuit and connect the microphone 
output to a pair of sensitive headphones.

6)  Use an external audio amplifier with input capacitive coupling 
and listen to audio from the microphone amplifier in your BITX.
This may be distorted due to mixer effects.

7)  Wire up a microphone bias circuit and use it to connect your 
microphone to a record player input.

8)  Wire up a microphone bias circuit and use it to connect your 
microphone to the audio input of a VCR or TV.

9)  Wire up a microphone bias circuit and use it to connect your 
microphone to an amplified computer speaker.

When building the microphone bias circuit it could be helpful to 
include connection to the PTT switch through an LED and current 
limiting resistor so you can test PTT operation at the same time.


On Sat, Jun 27, 2020 at 9:58 AM thomas.adair <thomas.adair@...> wrote:
How can I test my microphone to see if it is working? The radio receives well, but I not connect to anyone. With my digital voltmeter I unscrewed the jack, place the negative lead to the negative side of the jack and probed the center with the positive lead and actuated the PTT. 0 mV was the result.  

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