SI4721 datasheet(45/69 Pages) SILABS

45 / 69 page

AN383

Rev. 0.8

10. Whip Antenna for SW Receive on AMI (Si4734/35 Only)

The whip antenna is a typical monopole antenna used in portable SW receivers. Additionally, it can be used for FM

applications as covered in Section 6. This whip antenna schematic in this section will include the circuit for FM and

ferrite loop antenna for AM. In-depth analysis of the whip antenna for FM is covered in Section 6, while in-depth

analysis for the AM ferrite loop antenna is covered in Section 7.

10.1. SW Whip Antenna Design

The whip antenna is a monopole antenna with a stiff but flexible wire mounted vertically with one end adjacent to

the ground plane. The whip antenna is capacitive and its output capacitance depends on the length of the antenna

(maximum length ~56 cm). At 56 cm length, the capacitance of the whip antenna is about 12 pF at SW frequencies

and approximately 22 pF at the center of the FM band.

There are various types of whip antennas including the long non-telescopic metal whip antenna, telescopic metal

whip antenna, and rubber whip antenna. The following figure shows the rubber and the telescopic whip antenna.

Figure 28. Telescopic Whip Antenna

SI4721 Datasheet(PDF) 45 Page - Silicon Laboratories