If the LAVA antenna is amplified it requires 12 volt power which is sent up the coax. If this is the case, connecting a cable directly from the TV to antenna will not work. Also connecting to the cable TV connector will not work.
Many
"Digital TV" antennas are tuned mainly for UHF channels (14 thru 51) and work poorly for VHF channels (2 thru 13). Many newer RVs are using the King Jack antenna which doesn't do well for VHF channels. The NBC station KPNX broadcasts on VHF channel 12. Make sure the antenna is pointed in the right direction. Phoenix TV transmitters are located southeast of your location. If you have a Jack, the flat edge should point toward the transmitter.
Here's a link to an article by Chris Bryant that may help:
https://web.archive.org/web/20130814121735/http://blog.rv.net/2008/06/tech-tune-up-your-tv-antenna