Without seeing your set or schematic I would guess.......
The AM radio uses an internal ferrite loop stick antenna. Just like
almost all AM radios. Sometimes they provide an input for a
random length wire.
FM starts just above Ch 6. On most sets you can fine tune the TV
& start getting FM.
To my knowledge olden days antennas were not designed to reject FM
so everything can come in together. Newer antennas, at least the
Jerrolds I used had break off elements to reject FM. This was done
to better get Ch6 if it were fringe.
Bottom line is use a 75 to 300 ohm adapter to hook up FM & TV.
Be sure its rated to pass up to 800 MHZ.
For AM to add an external ant is involved You would have to couple
it to the loopstick by adding a winding. Hope that all helps.
73 Zeno
LFOD !