To reduce the amount of messages, the planes above 19,000 ft broadcast at 1080 MHz, and general aviation below 19,000 broadcast 978 MHz. Not as many messages on the 978 MHz frequency yet. Dump978 programs the software defined radio (SDR) to tune to that frequency, and then decodes the resulting data and it is merged with the Dump1080 data. It will require a second dongle tunable to 978 MHz, and antenna. The Blue FlightAware dongle has a filter in it and will probably be lousy at 978 MHz. The older yellow SDR dongle may work well on 978 MHz. I have not tried it, so wish you well.
Note, Antennas do not like to be too close to other antennas. The close distances affect the reception patterns. At these frequencies, 2 to 3 ft separation should help. Vertically, one ft separation will work well. Putting antennas just inches apart can cause all kinds of reception problems. I made these mistakes and thought it might be helpful for others to avoid the interactions.