Give it some time. Optimize for ADS-B tracking (gain, e-value) and see if that helps catch MLAT.
In my case I had problems getting MLAT with sample_rate of 20 MHz. I stuck with 12 MHz and high -e value since that seemed to produce the best total results for me. However, 20 MHz MLAT is probably worth the effort for you since I’m assuming you get a lot more MLAT traffic than I do here in the US. I’m not sure what the trick is for 20 MHz MLAT, it just never sync’d in my 20 or 30 minute tests in the past (I only get 15 to 25 MLAT per day so testing isn’t that easy).
If you set sample_rate to 20, you may need to decrease -e value to keep ADS-B CPU utilization reasonable.
In case it helps
- The best gain for me with Uputronics 1090 LN.A (about +16 db via bias-tee) was 20 (I thought this would be crazy high, but it worked best for aircraft count and msgs).
- I just started testing rtl-sdr blog triple filter LNA (+27 db) late yesterday and so far gain at 17 seems about the same as gain of 20 with the Uputronics, currently testing at 16 to see if I get better dynamic range.
Most people seem to suggest starting out with gain testing 17 or 18 and testing up or down a bit from there. It took me a long time to actually try 19 or 20 and the results in terms of plane count were significant and immediate.