One speaker is picking up radio module noise

[mik3ca]

Then again I looked at another site and they suggest I should include isolators at the antenna or speaker output connection. but which one tho?

So I did run more tests with the radio module disconnected and I never heard the oscillation. When I put the module back in again, I still get the oscillation as before every time I transmit data.

 

[ermine]

The audio line and the data cable are different


After reading literature, I decided to redo my PCB so that the audio output is more at the top left (farther away from the transmitter by at least one inch) and I made the ground plane bigger. I'll try a 10K resistor connected direct from input to ground and if that fails then I'll look into a small pf capacitor

Getting your radio further from the audio stage is good. The reason for taking the audio cable out is that somewhere in your system you have wires to the LM 386 acting as an antenna leading RF into the chip. You are trying to chase where this is coming into the chip. Obviously if you take the audio cable out you get no audio, but if the interference goes as well then you know that the audio input is one way it gets in.

Shame it seems the 100pf across the input of the LM386 doesn't help, it's the first obvious place. However, it normally wants some series resistance to help - in general any audio circuit wants about 100pf and some series resistance in to thin out any RF wanting to get in. Speaker cables are another way RF gets into your project, and you do of course have about 0.1uF close to the LM386 power pins as well as the big electrolytic PSU decoupling cap that I, ahem, can't see in your schematic. Every time I have used these, they hoot like banshees if I forget that, the datasheet ain't kidding you when it says

10 Power Supply Recommendations
The LM386 is specified
for operation up to 12 V or 18 V. The power supply should be well regulated and the voltage must be within the specified values.
It is recommended to place a capacitor to GND close to the LM386 power supply pin

When the man says close he means close - within 0.5 inch. You could do worse than look at the AM radio example in the datasheet to see how the manufacturer suggests you keep RF away from the chip - and that's just a receiver... You might want to put a bypass capacitor from pin 7 to ground, the datasheet is cagey about that but fig.2 gives you a hint, about 1uF would be good

I wonder if I could get things working by wrapping the entire radio module (minus antenna) first in electrical tape then in aluminum foil.

It's usually nice to ground the shielding - adhesive copper tape used to keep slugs off your plants is a good win there and easy to solder the ground wire to.

I did notice the interference went a bit fuzzled when I hooked a 100pF cap between adjacent pins of the radio module itself.

Which particular adjacent pins? Hopefully not the output and ground

Usually pays to be methodical about chasing RF problems, bypassing inputs, power supplies and then outputs. Always get your bypass caps as close to the LM386 chip as possible. What frequency is your radio system? Ferrite beads can help on your speaker output cables if it's a VHF or UHF system.

 

[mik3ca]

I'm gonna follow the advice on this because I haven't tried it yet: https://audiophile-musings.blogspot.com/2013/04/what-heck-is-ground-loop.html