Re: radio will transmit CW but not voice


I had another go at the whole thing tonight.  I resoldered most of the joints.  The issue is still the same.  When I scream into the microphone I get nothing.  If I switch to cw and key the mic I get tones.  I connected a 3.5 mm jack up to my frequency generator.  The head pin was positive and the top ring was ground.  If I shorted the middle ring with ground the radio would try to transmit.  I fed a 1kHz signal at a voltage level of 0.01V.  I wasn’t sure what level I should set, but I could just barely hear that signal with headphones.


I also checked the microphones on the oscilloscope.  I didn’t realize the voltage from them was so low.  I could see my voice when I screamed but not well for sure.  I don’t think the problem is the mic’s.  I took a picture of my board thinking that perhaps something is missing.  There are 2 components that are not filled in but perhaps they aren’t supposed to be there.


I am bummed about this thing.  I am relatively new to ham and I just wanted to get this working to get me more comfortable with the whole thing.


Thanks for the help and suggestions.


From: <> On Behalf Of W2CTX via
Sent: Sunday, April 18, 2021 11:33 AM
Subject: Re: [BITX20] radio will transmit CW but not voice


This may be an obvious statement but you say you key the mic.  Do you speak into the mic

to generate SSB signal?




On Saturday, April 17, 2021, 9:16:15 PM EDT, theaddies@... <theaddies@...> wrote:




I should have also said that I am using an SDR as a receiver.  On the waveform when I key the microphone I see nothing.  Whilst, when I key the microphone with CW selected I can see the signal loud and clear.




From: <> On Behalf Of Evan Hand
Sent: Saturday, April 17, 2021 8:38 PM
Subject: Re: [BITX20] radio will transmit CW but not voice



The first thing to do is always verify that the measurement is correct.  In this case that both rigs are set up to receive the other rig.  Same frequency and sideband.

Assuming that is correct, and still no audio, then I would suspect the microphone.  What test equipment do you have to help in diagnosing the issue?  At this point an oscilloscope would be nice, however, an RFProbe with a DMM can help in tracking the signal from the mic to the product detector/modulator if you do not have an oscilloscope.
Here is how to build one if you do not have an RF probe or oscilloscope:

Another test is to connect an audio tone source (your PC with an audio tone program as an example) and then key the PTT ring.  I made an adapter that connects the tip of a 3.5mm plug with the tip of the plug to the computer, shield to shield, and a switch between the shield and the ring of the plug that goes to the rig mic input.  If you get rf out of this setup then the mic is most likely the issue.

Let us know what test equipment that you have so we can give you suggestions based on your equipment.

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