What will create a "traffic puck" on the UAT band?
The answer is "yes" if 

a) you configure your 1090 out system to request ADS-B uplink at 978 MHZ (this feature was added to the message structure in DO-260B)
b) your 1090 ADS-B out message is confirming certain minimum "quality" standards related to both the quality of the position information (GPS Integrity or "NIC") and the quality of the avionics (SDA or system design assurance)and the quality of the install or SIL  The specifics of what quality message triggers the system is under review by the FAA, but if you equipment is certified (TSO'd) and the install is in accordance with AC-20/165B you will be fine.

Note, if you have a UAT ADS-B you can specify which uplink frequency you want in the same way.

Further note - almost all ADS-B system are single band transmitters (ADS-B Out) and dual band receivers (ADS-B In). 

Nuance - the uplink is broadcast to the quadrant (relative to the ground station) where you are flying.  This can lead to aircraft with no or "below quality" ADS-B out receiving traffic intended for another aircraft.  Depending on geometry this can create a partial traffic picture which can be quite misleading and potentially dangerous