Data Sheet

www.id-innovations.com
13
ID-2/12/20 LA Series Datasheet X1
11.04.2013
13. Designing Coils for ID-2LA
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-2LA 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.
For those who want a starting point into practical antenna winding it was found that 71 turns on a
120mm diameter former gave an inductance of 1.33mH.
Sometimes the antenna coil is necessarily surrounded by a metallic enclosure or has an adjacent
copper PCB plane. Both these can behave like a shorted turn. A shorted turn has the effect of
setting up a current in opposition to the ID-2LA antenna coil current and is analogous to adding a
negative inductance. Some range can be clawed back by either increasing the inductance or
increasing the capacitance. If the experimenter has an inductance meter that works at 100 KHz then
he can adjust the inductance back to 1.337mH by winding extra turns. Failing this an external
capacitance, C3, can be increased to offset the lower inductance and bring the antenna back to
tune.
Remember, that normally there is no need for external capacitance, because the ID2-LA has an
internal capacitor of 1N2, which perfectly tunes the recommended inductance of 1.337mH.
Warning. Do not exceed the stated maximum voltages and currents for the ID2-LA RF output.
Anybody who wishes to be more theoretical we recommend a trip to the Microchip Website where we found an
application sheet for Loop Antennas. All the same, once the user has got some theoretical knowledge, the advice of
most experts is to suck it and see. http://ww1.microchip.com/downloads/en/AppNotes/00831b.pdf