Hello - I’ve got a horrible high pitched whine in my node that i cannot seem to beat Originally, I had everything kind of haphazardly assembled, and the whine would vary greatly if I moved any component of the system, so in an effort to eliminate it, I built a shielded enclosure, and added all kinda of filtering nad shielding, and it won’t go away.
Currently, I have the PI sitting a few feet away from everything else. The fob is connected via a shielded USB cable that runs into an enclosure made of PCB blanks soldered together, and surrounding it completely, except fro the hole where the cable enters. The cable itself has a choke on all of the leads inside of the enclosure. The cables going from the enclosure to the radio are shielded, and have chokes. The power into the radios has chokes, and I added decoupling caps at the radios. The radios are also in shielded cases. The fob is also isolated from the radios via isolation transformers on both audio lines, and optos on the PTT and COS lines. The only electrical connection between the radios and the fob is via ground since they share a common power source, but even if I separate the power supplies I get the whine.
If I disconnect the RX radio, and key the TX radio, the sound is there until I unplug the fob from the PI. Moving literally anything, changing anything about the antenna output, or touching anything changes the volume of the noise.
I’ve seen other people alluding to this issue, the only one who fixed it fixed it by adding a choke on the USB, which i have done. Someone else said it was due to the buck converter for the 3v3 on the CM108, in which case I don’t know how it would be possible to eliminate.
Any ideas? I’m at my wits end with this.