Try grounding your audio input and see what happens.
Sounds like a ground hum loop to me then. There is a difference in voltage between your audio input ground and the LM317 ground. You should have a capacitor (at least 10uF) from the input pin of the LM317 to the emitter of the 2N2222 and the audio ground should also be connected directly to the emitter. Use a star connection, everything audio returned to the same physical point so they must be at the same potential.
Brian.
Weird? I´m not sure.Weird, changing the ground point a few CM away in the PCB changes the TX carrier level and hence the modulation.
Hi,
Weird? I´m not sure.
This is why a solid GND plane is that important (Like I very often write in my posts).
And then one can see that there is a big difference between copper filled layer and a true GND plane layer.
If you need some support with GND plane: just show us your PCB layout.
Klaus
Hi,
not that bad.
Such copper arts usually are much better than any breadboard...or single layer PCB.
Klaus
Sounds like a ground hum loop to me then. There is a difference in voltage between your audio input ground and the LM317 ground. You should have a capacitor (at least 10uF) from the input pin of the LM317 to the emitter of the 2N2222 and the audio ground should also be connected directly to the emitter. Use a star connection, everything audio returned to the same physical point so they must be at the same potential.
Brian.
Only that there is no frequency modulation on the carrier. When receiving in CW mode you probably wouldn't hear very low frequencies because of the receiver audio filtering.I notice this hum only when switching the RX to AM. On CW no hum is heard. Does this tell you something?
The hum gets louder. But I am touching the shorting metal with my hand...What happens if you short out the audio input, with and without the audio cables connected?
Brian.
Hm... But I have tested this with the simple linear PSU and also with the LAB psu, which has a ground (the mains ground)That suggests you are becoming part of the signal path.
Can you check that the PSU you are using really has a ground connection. There should be one but I'm thinking if you are using a laptop supply it might have a two pin mains connector and if I'm right, there would be no ground at all on your gadget except through the audio cable.
Brian.
Hm... But I have tested this with the simple linear PSU and also with the LAB psu, which has a ground (the mains ground)
Don’t confuse mains ground with the negative supply terminal; they’re generally isolated.it’s the negative terminal(common) that needs attention.
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