If the antenna is shorted, this is what you'll observe.
Touching just the center pin alone will turn the outside surface of the coax into a demented receiving antenna.
But connecting the shield to the grounded outer part of the socket turns that coax braid into a shield. Keeps out all RF signals.
If your antenna is toast, that can cause this problem
If the center-wire connection at the far end of the coax is broken, you'll see this symptom.
If the far end of the coax is shorted from center wire to shield, you'll see this symptom.
And if someone has pushed a straight pin through the coax outside the house, this will short the center wire to the shield braid and cause this symptom.
Troubleshooting a fault is a process of elimination, finding all the parts of the system that are NOT bad, one by one. Eventually this will lead you to what HAS gone bad.
A SWR meter is a handy tool to keep around a base station. Even if an antenna is perfect when you put it up, it won't stay that way forever. Anything you put outside into the weather and sun will deteriorate, no matter what it is.
The coax plug at the bottom of the antenna must be waterproofed. If you don't, the connector will soak up rainwater like a sponge. Capillary attraction will suck that water down inside the coax, between the strands of the shield braid.
Bad juju when that happens.
Soldering the shield braid to the plug is not easy. Lots of folks just fold over the braid and call it good enough. So long as you don't mind replacing that connection a few times a year, it will be. Soldering the braid to the plug prevents the copper strands from oxidizing and disturbing the metal-to-metal contact between the braid and the body of the plug. Makes it last longer.
And yeah, putting up a base antenna should be simpler.
73