Noisy feed - RTLDSR-Airband

[freema22]

Hi team,
I just updated my feed to use an RTL-SDR and RTLSDR-Airband. I'm wondering if any of you could listen to some of my archived feeds and give me some ideas as to what adjustment I need to make to the .conf file. The feed has a loud hum and is very noisy. I suspect my gain setting is too high, at 25. It also seems that the RTL-SDR is not nearly as sensitive as the old scanner/USB soundcard configuration I was using before, as there are a lot of missed radio calls. I suspect the auto squelch that RTLSDR-Airband uses is a little aggressive. I'm interested in feedback there as well. Thanks for helping me fine-tune my setup.

Oakland County International Airport (KPTK) Tower Audio Archives

 

[wgbecks]

Hi team,
I just updated my feed to use an RTL-SDR and RTLSDR-Airband. I'm wondering if any of you could listen to some of my archived feeds and give me some ideas as to what adjustment I need to make to the .conf file. The feed has a loud hum and is very noisy. I suspect my gain setting is too high, at 25. It also seems that the RTL-SDR is not nearly as sensitive as the old scanner/USB soundcard configuration I was using before, as there are a lot of missed radio calls. I suspect the auto squelch that RTLSDR-Airband uses is a little aggressive. I'm interested in feedback there as well. Thanks for helping me fine-tune my setup.

Oakland County International Airport (KPTK) Tower Audio Archives

You're correct that the squelch functions of SDR receivers leave a lot to be desired, regardless of demodulating AM or FM transmissions.
I'd like to look at your rtl_airband.conf file if you'd care to post it.

 

[freema22]

You're correct that the squelch functions of SDR receivers leave a lot to be desired, regardless of demodulating AM or FM transmissions.
I'd like to look at your rtl_airband.conf file if you'd care to post it.

Thanks for the quick response. Here's the part that matters:

 

[wgbecks]

Thanks for the quick response. Here's the part that matters:
View attachment 176114

Not at all useful. I am interested in looking at how you've configured the "Outputs: section. You can redact anything confidential.
However, if you're sending the audio directly to BCFY using Icecast, then your noise is not actually an audio problem, but is more likely
RF interference or overload from other strong signals in the spectrum.

 

[freema22]

Yes, I am feeding directly to BCFY with Icecast. Not sure if the interference is coming from the Pi itself or elsewhere. I did not have this noise issue when using a scanner and USB soundcard.

 

[wgbecks]

Yes, I am feeding directly to BCFY with Icecast. Not sure if the interference is coming from the Pi itself or elsewhere. I did not have this noise issue when using a scanner and USB soundcard.

Are you using an indoor or an outdoor antenna? It's very likely that you're either hearing RFI from a local source or perhaps that the SDR
is getting overloaded with strong nearby signals that is causing the issue Antenna's being equal, the scanner would be a better receiver
that an RTL SDR and deal with a busy spectrum much better.

You could pull the SDR and connect it to a PC and run a program like SDR# tuned to the aviation band to have a look at the spectrum
surrounding the desired frequency or frequencies broadcast on your feed.

 

[freema22]

I know I am going to jinx myself, but I may have fixed it. I had the RTL-SDR jammed into the USB slot on the RPi right under the Wifi dongle. I got a USB extension and moved the SDR physically further away. I also snapped on a ferrite on the extension just incase. The audio sounds 100% better.

 

[ChrisABQ]

Care to share an audio sound clip of the fix? I'm currently feeding bcfy with local ATC using a scanner and may switch to sdr dongles. My first thought about the hum was using a ground loop isolator.

 

[wgbecks]

My first thought about the hum was using a ground loop isolator.

The rtl_airband configuration in use by @freema22 sends audio directly in the digital domain as MP3 to BCFY and does not breakdown to raw audio where you'd consider installing a ground loop isolator between the receiver (scanner) and PC soundcard.

It appears his noise was due to RFI getting into his SDR from the WiFI dongle.