SI4721 datasheet(39/69 Pages) SILABS

39 / 69 page

AN383

Rev. 0.8

8. Ferrite Loop Antenna for AM/LW Receive on AMI (Si4730/31/34/35/36/37

Only)

There are two types of antenna that will work well for an AM receiver: a ferrite loop antenna or an air loop antenna.

A ferrite loop antenna can be placed internally on the device or externally to the device with a wire connection.

When the ferrite loop antenna is placed internally on the device, it is more susceptible to picking up any noise

within the device. When the ferrite loop antenna is placed outside a device, e.g., at the end of an extension cable,

it is less prone to device noise activity and may result in better AM reception.

8.1. Ferrite Loop Antenna Design

Figure 24 shows an example of ferrite loop antennas. The left figure is the standard size ferrite loop antenna. It is

usually used in products with a lot of space, such as desktop radios. The right figure is the miniature size of the

loop antenna. It is usually used in small products where space is at a premium, such as cell phones. If possible,

use the standard size ferrite loop antenna as it has a better sensitivity than the miniature one.

Figure 24. Standard and Miniature Ferrite Loop Antennas

A loop antenna with a ferrite inside should be designed such that the inductance of the ferrite loop is between 180

and 450 µH for the Si473x AM Receiver.

Table 17 lists the recommended ferrite loop antenna for the Si473x AM Receiver.

The following is the vendor information for the ferrite loop antennas:

Guangzhou Jiaxin Electronics Shenzhen Sales Office

email:sales@firstantenna.com

Web:www.firstantenna.com

Table 17. Recommended Ferrite Loop Antenna

Part #

Diameter Length

Turns

Type

Application

SL8X50MW70T

8 mm

50 mm

400

Mn-Zn

Desktop Radios

SL4X30MW100T

4 mm

30 mm

100

300

Ni-Zn

Portable Radios

(MP3, Cell, GPS, …)

SL3X30MW105T

3 mm

30 mm

105

300

Ni-Zn

SL3X25MW100T

3 mm

25 mm

110

300

Ni-An

SL5X7X100MW70T 5 x 7 mm 100 mm

400

Mn-Zn

Desktop Radios

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