The recommended Inductance is 1.337mH to be used with the internal tuning capacitor of 1n2. In general the bigger the antenna the better, provided the reader is generating enough field strength to excite the tag. The ID-3LA is relatively low power so a maximum coil size of 15x15cm is recommended if it is intended to read ISO cards. If the reader is intended to read glass tags the maximum coil size should be smaller, say 10x10cm.
Long read ranges, up to 30cm and more, can be achieved with Innovations Long Range Clamshell Cards using 10x10cm Antennas. There is a science to determine the exact size of an antenna but there are so many variables that in general it is best to get a general idea after which a degree of ‘Try it and see’ is unavoidable. If the reader is located in a position where there is a lot of heavy interference then less range cannot be avoided. In this situation the coil should be made smaller to increase the field strength and coupling. It is difficult to give actual examples of coils for hand wounding because the closeness and tightness of the winding will significantly change the inductance. A professionally wound coil will have much more inductance than a similar hand wound coil.