Kevin,
Assuming you are referencing 319 MHz and 345 MHz sensors, the loop is specific to the device type and sometimes the manufacturer. There is not really a standard that manufacturers follow for 319 MHz and 345 MHz devices, so it can vary from one device to another.
We have some documentation based on the 319 MHz sensors we offer, along with additional information on the 345 MHz sensors we have tested. I will link those documents below.
Max Out 345mhz Sensor Settings
If you have questions about specific devices, please let us know and we will do our best to help identify the proper loop.
Thanks again,
Mike