I (not recently because it's been too long due to me being busy) got an FM transmitter. I wanted to broadcast loud and with a very good signal! I mean, of course, I am a perfectionist. Haha
When I tried to broadcast, I got a huge amount of tilt up & down showing up on my RTLSDR on the MPX. Including a lot going out of bounds of the 200khz bandwidth. If I used a highpass filter on stereotool and removed all the bass to 150hz it would fix it.
I tried using the Tilt Correction on Stereo Tool. I wasn't able to fix the tilt (or not enough for me to notice).
Using that, I would be able to make square waves straight at around ~100khz when testing those but it wouldn't be able to fix the issue. Plus, adding more tilt correction would just end up increasing the modulation level and making the square waves not straight.
I then got the HiFiberry sound card as it was recommended as a cheaper way but provides a good signal. I was thinking it would be better but it wasn't. It still had the same problem as a Realtek ALC892 I have on my PC and as another Realtek from an old PC I had laying around.
The FM transmitter is from PCS Electronics which said it would produce a good signal. I even tried contacting them about this issue and they told me it wasn't an issue with the FM Transmitter.
My setup:
Yeah, I do not have the proper equipment for looking at modulation levels. That may also be an added problem. I am using RTLSDR and outputting MPX to a virtual audio cable. I am using MPXTool to look at the output.
Currently, I am outputting from HiFiberry on the raspberry pi. Stereotool is running on the raspberry pi 4b. I have RCA cables connected to the Fm transmitter from the hifiberry. I have the FM Transmitter set to MONO.
This is what the tilt looks like:
I could send an MPX recording if you helpful.
Any feedback would seriously be so helpful on how to fix this!