They are a standard size.
Assuming the threaded connector on the antenna engages with the threads on the 75 ohm connection on the tuner and tightens normally (it should if both are undamaged), then the problem is often that the center bare wire that inserts into the connection is too short to make proper contact.
Possible solutions (in order to try:
1) The connection on the antenna you bought probably should work but doesn't. Return the antenna you bought and get a different one and try that. If that doesn't work....
2) Assuming the tuner has a 2 terminal 300 ohm flat wire connection also, also pick up a 75 to 300 ohm adapter while at Radio Shack, attach the current 75 ohm lead to that and then the two wires from the adapter to the 300 ohm terminals on the tuner and see if that now works.
3) If 1 or 2 doesn't work, and your tuner has the 300 ohm 2 wire conenction, return the antenna and just get a simple 300 ohm FM dipole wire antenna and attach that to the 300 ohm antenna terminals on the tuner. This is often the failsafe thing to do and the cheaper dipole often will match or outperform many fancier indoor FM antennas that you might try otherwise.
Good luck!
Assuming the threaded connector on the antenna engages with the threads on the 75 ohm connection on the tuner and tightens normally (it should if both are undamaged), then the problem is often that the center bare wire that inserts into the connection is too short to make proper contact.
Possible solutions (in order to try:
1) The connection on the antenna you bought probably should work but doesn't. Return the antenna you bought and get a different one and try that. If that doesn't work....
2) Assuming the tuner has a 2 terminal 300 ohm flat wire connection also, also pick up a 75 to 300 ohm adapter while at Radio Shack, attach the current 75 ohm lead to that and then the two wires from the adapter to the 300 ohm terminals on the tuner and see if that now works.
3) If 1 or 2 doesn't work, and your tuner has the 300 ohm 2 wire conenction, return the antenna and just get a simple 300 ohm FM dipole wire antenna and attach that to the 300 ohm antenna terminals on the tuner. This is often the failsafe thing to do and the cheaper dipole often will match or outperform many fancier indoor FM antennas that you might try otherwise.
Good luck!