Texas Instruments 2000 LF Series, Application Note, Page: 28 / 38

Lit Number: 11-06-21-068
Page (22)
Texas Instrument’s antennas use heat shrink (method A) to hold the two Litze wires
together but plastic braid (method B) is a less expensive substitute. Method C relies
on the figure-of-eight construction of the ‘Jumbo’ Hi-Fi wire but the method will always
have a join in the wires between the loop and tail and cannot be recommended for
moist or wet conditions. For road loops method D is preferred and the twist is
achieved by using a portable electric drill. The disadvantage of this method is that it
increases the resistance and inductance because of the extra wire.
4.6 Ferrite Cored Antennas
Ferrite cored antennas, like Texas Instrument’s stick antennas (RI-ANT-S01C and RI-
ANT-S02C) provide a strong localized RF field and perform well in noisy
environments. They are easy to construct but do need the correct grade of ferrite for
the core – Texas Instruments recommend Philips 3F3 grade. Figure 26 shows the
design of a small, 60 mm (2.4”) long antenna.
Figure 26. Ferrite Cored Antenna
5 Other Antennas
5.1 Field Lines
Texas Instruments LF system uses the magnetic (H) field to transfer energy to the
transponder. When a current moves through an antenna it generates field lines similar
as those shown in Figure 27.