I've read through your other thread on your sdr previously, and I'm glad to see you've gotten to this point! I have also purchased a rtl-sdr recently, and managed to get it working in the way you're looking for. Personally, I'm using UniTrunker instead of airspy, the rest is the same.
First and foremost is the antenna. Are you using the antenna that came with the kit, or are you using something else? If you're using the one with the kit(assuming the current kit available), then we get to play around a bit here. It helps to know your control frequency, as it's going to be key for this. The antenna that comes in the kit is essentially just a beginner antenna. You can do some pretty amazing stuff with it nonetheless, but it requires a bit of tuning. The following assumes you are using the current kit available.
https://www.rtl-sdr.com/dipole
Scroll down to the part labeled "
Choosing the Antenna Element Length"
There is a cheat sheet that tells you the roundabout length for certain frequencies. You can use this as a rough guide instead of flying blind. Additionally, there is a link to a dipole calculator. Input your control frequency, select "One Side" and click "Calculate." This will give you the recommended length of each of the antenna. Just extend them to the measurement calculated! The next step is configuration and orientation. Going back to the link above, the next section is labeled "
Using the Mounts" For the current purposes, having the antenna in a line, and vertical, is what I'd recommend.
With the kit antenna, I found placement to play a big part as well. This will apply to any antenna as well if I understand correctly. Is it close to metal? The wall? Is it inside or outside? For me, my drywall isn't healthy for the signal, neither is metal. UniTrunker has a handy "health status", which basically gives you an idea how good of a signal you're getting. The one window, and apologies for not recalling what it's called, shows bars at the top left. They will change from red, to yellow, to green, depending how good the application thinks your reception is. This can help you determine where to place your antenna. I'm also in an apartment, so it can get pretty tricky. Having that visual representation helps a lot.
Another issue could be calibration. Unfortunately, I don't understand it enough to give you a good explanation or how-to, so google "rtl sdr ppm correction" and read what pops up on the forums here. My device, miraculously, has no need to be corrected. This correction applies in SDR# and UniTrunker(if you decide to use it)
One plus side of UniTrunker is the ability to switch around frequencies(to extent), as well as perform lockouts on talkgroups. Additionally, you can name your talkgroups in accordance with the database here on radio reference. The one part that
really[/u] solved it for me was it telling me what talkgroup I was hearing. In UniTrunker, the frequency being broadcast to DSD+ gets highlighted in green(I think it's default color), as well as the talkgroup transmitting. I found most of the dead air, or "junk" I got was just encrypted channels. The database here has info on if a talkgroup is encrypted. For me, DSD+ tells me it's muting the audio tho when it's being converted, so if you don't get a message, your issue may be reception, or elsewhere.
A handy device I learned about, that could be of use for you, is a low noise amplifier. This is useful if you're in a more rural area and the towers are far away. Of course, it can't beat good antenna placement.
Here are two links that helped me get UniTrunker working, which I'd highly recommend you use. The program looks complicated, but it really isn't. I was able to get it all working within 2 hours of getting my kit and after troubleshooting a bit. I'm able to get a usable signal most of the time, tho I have a slight lack of unencrypted channels.
https://www.youtube.com/watch?v=pN9-1unOsu0
https://www.rtl-sdr.com/rtl-sdr-tutorial-following-trunked-radio-unitrunker/ (scroll to "Monitoring with only One Dongle" if only one rtl-sdr. The section after tells you how to set it up to pipe to DSD+)
I hope this all helps! Go through the antenna setup first, and then UniTracker and let me know your results!
