The issue on 39602 has been resolved and here’s what I did to fix it.
Eric’s suggestion of changing the gain setting from -10 (Auto Gain Control) to 44 is almost perfect for my setup. Before I had few aircraft below 7000 to 9000 AGL and can now see the local Police helicopters patrolling at lower altitudes. The weather here right now is not suitable for the small aircraft not certified for none-icing.
My RSSI numbers, displayed by closing the map in Skyview, originally had 30 to 40 aircraft that were in the 0 to -3 range Eric spoke of and it is now down below 5 aircraft. I set it to 44 as wiedehopt suggested.
wiedehopt’s comment and link to (Thoughts on optimizing gain) was a big help and thank you for that reply.
My Unit is an RPi 3B+ running Raspbian Stretch with PiAware installed over the net. These commands using SSH taken from wiedehopts link did the trick. Note: changing the gain setting in the piaware-config file has no effect on this installation.
Raspbian image written to microSD card, then Piaware Add-on Package and dump1090-fa Add-on package installed
(Raspbian image downloaded from https://www.raspberrypi.org/downloads/raspbian/
Piaware and dump1090-fa Add-on packages installed as per instructions on https://flightaware.com/adsb/piaware/install 4 )
(a) In this example gain is set to 30. Instead of 30 use the gain value you want to set
(b) Gain is set to 29.7 instead of 30 as shown in last line. This is due to fact that dongle cannot be set to any value, but to one of the permissible values nearest to the value you specify in the gain setting command.
Open file /etc/default/dump1090-fa in nano to edit it
sudo nano /etc/default/dump1090-fa
Above command will open file /etc/default/dump1090-fa which has following content:
# dump1090-fa configuration
# This is read by the systemd service file as an environment file,
# and evaluated by some scripts as a POSIX shell fragment.
# If you are using a PiAware sdcard image, this config file is regenerated
# on boot based on the contents of piaware-config.txt; any changes made to this
# file will be lost.
RECEIVER_OPTIONS="--device-index 0 --gain -10 --ppm 0 --net-bo-port 30005"
NET_OPTIONS="--net --net-heartbeat 60 --net-ro-size 1000 --net-ro-interval 1 --net-ri-port 0 --net-ro-port 30002 --net-sbs-port 30003 --net-bi-port 30004,30104 --net-bo-port 30005"
In the line starting with RECEIVER_OPTIONS, change the gain value from -10 to the required value. In this example it will be changed to 30.
Line before change:
RECEIVER_OPTIONS="–device-index 0 –gain -10 --ppm 0 --net-bo-port 30005"
Line after change:
RECEIVER_OPTIONS="–device-index 0 –gain 30 --ppm 0 --net-bo-port 30005"
After changes are made as above, save changes (Ctrl+o) and close file (Ctrl+x)
Restart dump1090-fa to implement the newly set gain value
pi@raspberrypi:~ $ sudo systemctl restart dump1090-fa
Verify that the new value of gain is actually implemented
pi@raspberrypi:~ $ sudo systemctl status dump1090-fa -l
The last line of output of above command will show gain actually set
piaware dump1090-fa: rtlsdr: tuner gain set to 29.7 dB