I’m using a splitter with my amplified 1090 coco which is mounted about 40 feet up. It has seen 978 traffic up to about 50-55 miles away even though I’m surrounded by tall trees. I’m also planning a dedicated 978 antenna eventually.
As others have mentioned, there isn’t a large volume of 978 traffic in the US yet. I usually see about a dozen or so aircraft a day, but I am not located in a busy area.
I’m still having a problem with 978 traffic showing up on 1090. Sometimes it does and most times it doesn’t. I eventually ended up using jprochazka’s scripts at: https://discussions.flightaware.com/ads-b-flight-tracking-f21/ads-b-feeder-project-setup-scripts-t36532.html
It allow you to set up everything, dump1090-mutability, dump978, flightaware and performance graphs fairly easily. All the different setups which I have tried still have a problem with most of the 978 traffic not showing on the 1090 map. I’m still working on that.