Yes, you used the correct case.
Whenever you want to check if you have used correct method and the gain has actually set to the desired value, give following command and read the LAST line of output. It will show what gain value is actually set.
sudo systemctl status dump1090-fa -l
- The dongle gain can only be set to a value between 0 and 49.6
- The dongle does NOT accept any negative (-) value of gain.
- The gain value -10 is a special number. It does NOT sets gain to -10 . It SWITCHES dongle into AGC mode (Automatic Gain Control mode). In this mode the dongl dynamically adjusts gain according to received signal strength.
-gain 30 given in the “How To” was an example only, and did not mean you adjust your dongle to it. The gain value to be used varies over a wide range, depending on antenna, location, dongle, amplifier etc. The optimum value for any setup is to be determined by trial and error i.e. try different values of gain and watch performance for each value of gain.
For your setup with 1/4 wave ground plane antenna indoors, the best is to keep it at the default setting of AGC (i.e. at