Rev. 0.2 4/08 Copyright © 2008 by Silicon Laboratories AN316

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AM/FM TUNER FIELD TEST PROCEDURE

1. Introduction

This document describes the recommended field test procedures for Silicon Laboratories AM/FM tuners. Fieldtests listed in this document exercise the tuners with radiated signals. It is beneficial to perform field tests sincethese will simulate the user performance more closely than bench tests.

Due to the nature of radiated tests, consistency regarding test parameters is crucial. Parameters such as location,environment, position, and orientation of the equipment should be the same when comparing different devices. Itshould be noted that all results obtained following the procedures in this document are relative measurements.

Table 1. AM/FM Tuner Field Test Equipment

Test Equipment

Channel Rating

Device Under TestAntenna(s) to be used with the DUT

Seek Performance

IP3

Image Rejection

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2. Channel Rating

1. Set up the DUTs with the desired antennas.

2. Tune to every local AM/FM radio station and rate the sound quality according to the following flow chart.

Figure 1. Channel Rating Flow Chart

Do you recognize any sound?

0

Do you experience static >50% of the time?

NO

YES

4

Can you eliminate static?

3

1

2

NO NO

NO

YES

YES

Can you generate static?

YES

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3. Recognizing a sound means being able to identify a spoken word or music coming from the headphone or speakers, even if there is static with it. Rate 0 if static is all that can be heard.

a. If you experience static more than 50% of the time, try to eliminate it by unwinding the headphone cable and moving it to different positions or orientations. Different orientations include positions in all axes; x, y, and z. If you are using an antenna other than the headphones, you can change its orientation as well.

i. Rate 1 if these changes do not remove static completely.

ii. Rate 2 if they remove static completely.

b. If there is no static more than 50% of the time, try to generate it by winding the headphone cable and moving it to different positions or orientations. If you are using an antenna other than the headphones, you can change its orientation as well.

i. Rate 3 if these changes generate any static.

ii. Rate 4 if the sound is always clear.

See "FM Channel Rating Examples" on page 5 for channel rating test results. While performing the field tests onyour device, you can use another tuner with comparable performance as a benchmark device. During testing youwill notice that even a small average rating difference between two devices translates into a significant difference inlistening experience.

To get a full list of stations available in a particular area, you can refer to websites that share radio locationinformation. An example can be found at http://www.radio-locator.com/

3. Seek Performance

Seek performance can be tested in different locations to verify performance under weak and strong signalenvironments. For weak performance area you can use a rural location, and for strong signal environment you canuse an urban location.

While conducting a seek performance test, make sure you have the same orientation for all antennas of the sametype. If trying different antennas, record the antenna type and orientation in your test results.

1. Setup the DUTs with the desired antennas.

2. Search for radio stations using the auto scan function of the device (if available) or using the seek function. Record all the stations that the device recognizes.

3. Check whether the station was found at its correct frequency, and record it as valid or invalid.

When a device recognizes a station at an incorrect frequency, it is usually one channel up or down from the correctone, otherwise it might be an image or third order intermodulation product.

See "FM Seek Performance Example" on page 6 for test results.

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4. IP3

In strong signal strength environments, intermodulation product of two strong channels might fall on top of a validchannel or can be detected as a station at a frequency that it's not intended to be transmitted. A good measure ofintermodulation distortion is IP3. IP3 is the theoretical RF level at which two blockers offset from the desiredfrequency by f and 2f, and their intermodulation product would be of the same amplitude. This test evaluates theIP3 performance of tuners under such conditions.

1. If a radio station is at frequency F1 and another station is at F2, IP3 occurs at frequencies 2 × F1 – F2 and 2 × F2 – F1. Calculate the IP3 frequencies for every pair of strong stations (stations that had ratings 3 and 4 in the channel rating test). Only consider pairs of stations that are more than 0.5 MHz apart in FM band and more than 180 kHz apart in AM band. This is to make sure that the station heard is a result of IP3 and not an image of it (See the image rejection test below for details.) Create a list showing the calculated IP3 frequencies and the generating stations for each IP3. Another method of selecting strong stations is to perform an RSSI scan and choose the stations with high RSSI values. The channel spacing recommendations are for Si47xx receivers. For other DUTs, choose channels to avoid the image frequency of the specific DUT.

2. Setup the DUTs with the desired antennas.

3. Tune to each IP3 frequency on the list, and try to recognize any sound. Compare it to the respective generating stations, and record the IP3 frequency if it outputs the same audio as one of those stations. Normally the audio from an IP3 frequency has a lower sound quality. Repeat the same for the other device and compare results.

See "FM IP3 Example" on page 8 for test results.

5. Image rejection

In strong signal environments, another interferer might be the image frequency of the desired channel.

1. Setup the DUTs with the desired antennas.

2. Audible images are usually caused by strong stations (stations that had ratings 3 and 4 in the channel rating (outdoor) test.) In FM band, for each strong station, tune to the frequencies that are 0.2 to 0.3 MHz (or at the image frequency for the DUT) below or above the correct frequency for the station, and try to recognize any sound. In AM band, for each strong station, tune to the frequencies that are 90 to 100 kHz (or at the image frequency for the DUT) below or above the correct frequency for the station. Compare it to the station at the correct frequency, and record the image frequency if it outputs the same audio as the station. Normally the audio from an image frequency has a lower sound quality.

See "FM Image Rejection Example" on page 9 for test results.

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APPENDIX—EXAMPLES

IntroductionIn these examples, test results are shown for radio stations in Austin, TX with different cell phones.

FM Channel Rating Examples

Frequency (MHz) Code Station Name Competitive Solution #1

Competitive Solution #2

Si470x

88.1 KNLE Candle-88 1 1 088.5 KYCM88.7 KAZI The Voice of Austin 4 4 489.5 KMFA Voice of the Arts for Central Texas 4 3 489.9 KTSW The Other Side of Radio90.5 KUT National Public Radio 3 3 391.3 KNCT91.7 KOOP Austin Co-op Radio 3 4 492.1 KQJZ K-Love92.5 KKLB Club 92.5 3 2 393.3 KDHT Hot 93.3 3 2 393.7 KLBJ Austin’s Rock Classic 4 3 494.7 KAMX Mix 94.7 4 3 495.5 KKMJ Majic 95.5 3 3 496.7 KHFI 96.7 Kiss FM 3 3 498.1 KVET 98.1 KVET 4 4 498.5 KRXT Real Country 2 2 298.9 KHHL Exitos 98.9 3 3 499.3 KLGO The Word99.7 KDHT Hot 99.7 1 1 1100.1 Pirate 1 1 2100.7 KASE Kase 101 4 3 3101.5 KROX 101-X 4 4 4101.9 KACQ 0 2 0102.3 KPEZ 102.3 The River 4 4 4103.5 KBPA Bob FM 3 3 4104.3 KQBT The Beat 104.3 2 1 1104.9 KXXS Sol Música Romántica 4 3 3105.1 KMHF 0 1 0105.9 KFMK Jammin 105.9 4 4 4106.3 KQQT K-Love 1 1 1106.7 KXPW Power FM106.9 KHLB107.1 KGSR Radio Austin 4 4 4107.7 KINV La Recuerda 2 1 1107.9 KFAN Que Buena

Channel Rating Total 78 73 79Total # Valid Stations 28 28 28

Average Rating 2.78 2.61 2.82

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FM Seek Performance ExampleLegend:

x: invalid seek.

: valid seek;

Frequency (MHz) Code Station Name Competitive Solution

Si470x

88.1 KNLE Candle-88

88.5 KYCM

88.6 x

88.7 KAZI The Voice of Austin

89.5 KMFA Voice of the Arts for Central Texas

89.9 KTSW The Other Side of Radio

90.5 KUT National Public Radio

91.3 KNCT

91.7 KOOP Austin Co-op Radio

92.1 KQJZ K-Love

92.5 KKLB Club 92.5

93.1 x

93.3 KDHT Hot 93.3

93.7 KLBJ Austin’s Rock Classic

94.4 x

94.7 KAMX Mix 94.7

95.4 x

95.5 KKMJ Majic 95.5

96 x

96.4 x

96.7 KHFI 96.7 Kiss FM

97.6 x

98.1 KVET 98.1 KVET

98.5 KRXT Real Country

98.8 x

98.9 KHHL Exitos 98.9

99.3 KLGO The Word

99.7 KDHT Hot 99.7

100.1 Pirate

100.4 x

100.7 KASE Kase 101

101.5 KROX 101-X

101.9 KACQ

102.1 x

102.3 KPEZ 102.3 The River

Note: Stations in red are invalid stations that the devices reported during seek.

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102.7 x

103.5 KBPA Bob FM

104 x

104.3 KQBT The Beat 104.3

104.9 KXXS Sol Música Romántica

105.1 KMHF

105.8 x

105.9 KFMK Jammin 105.9

106.3 KQQT K-Love

106.7 KXPW Power FM

106.8 x

106.9 KHLB

107.1 KGSR Radio Austin

107.7 KINV La Recuerda

107.9 KFAN Que Buena

Total number of valid stations 18 19

Total number of invalid stations 15 0

Frequency (MHz) Code Station Name Competitive Solution

Si470x

Note: Stations in red are invalid stations that the devices reported during seek.

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FM IP3 ExampleThe table below shows all the strong stations from the channel rating example and their IP3 components. Forsimplicity, only stations with a rating of 4 have been chosen.

Legend:

x: Cannot hear any of the generating signals at the IP3.

Frequency OR can only hear the radio channel that is at the IP3 frequency (in cases where the IP3 product is ata frequency where there is a radio channel.)

: Can hear either of generating channels.

1: Can hear generating signal 1 at the IP3 frequency.

2: Can hear generating signal 2 at the IP3 frequency.

3: Can hear both generating signals at the IP3 frequency.

IP3 Frequency (MHz)

Generating Channel 1

Generating Channel 2

Competitive Solution

Si470x

87.9 88.7 89.5 x x

90.3 88.7 89.5 x x

98.7 88.7 93.7 x x

97.9 89.5 93.7 (2) x

89.3 93.7 98.1 x x

107.5 88.7 98.1 x x

106.7 89.5 98.1 x x

102.5 93.7 98.1 1 x

94.7 98.1 101.5 x x

93.9 98.1 102.3 x x

90.3 98.1 105.9 x x

89.1 98.1 107.1 x x

104.9 98.1 101.5 (3) x

100.7 101.5 102.3 x x

97.1 101.5 105.9 x x

95.9 101.5 107.1 x x

106.5 98.1 102.3 x x

103.1 101.5 102.3 x x

98.7 102.3 105.9 (1) x

97.5 102.3 107.1 (2) x

104.7 105.9 107.1 (2) x

Total # channels with intermodulation problems 6 0

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FM Image Rejection ExampleThe table below shows all the strong stations from the channel rating example. For simplicity, only stations with arating of 4 have been chosen. Listening test checks whether the image frequency should be heard on these strongchannels.

Legend:

x: Cannot hear the original station at the image frequency.

: Can hear the original station at the image frequency.

Original Frequency (MHz) Competitive Solution

Si470x

88.7 x x

89.5 x

93.7 x

98.1 x x

101.5 x

102.3 x x

105.9 x

107.1 x

Total # of channels where image frequency is audible

5 0

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NOTES:

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DOCUMENT CHANGE LIST

Revision 0.1 to 0.2 Added AM Receiver Information.

Corrected information on Image Rejection definition.

DisclaimerSilicon Laboratories intends to provide customers with the latest, accurate, and in-depth documentation of all peripherals and modules available for system and software implementers using or intending to use the Silicon Laboratories products. Characterization data, available modules and peripherals, memory sizes and memory addresses refer to each specific device, and "Typical" parameters provided can and do vary in different applications. Application examples described herein are for illustrative purposes only. Silicon Laboratories reserves the right to make changes without further notice and limitation to product information, specifications, and descriptions herein, and does not give warranties as to the accuracy or completeness of the included information. Silicon Laboratories shall have no liability for the consequences of use of the information supplied herein. This document does not imply or express copyright licenses granted hereunder to design or fabricate any integrated circuits. The products must not be used within any Life Support System without the specific written consent of Silicon Laboratories. A "Life Support System" is any product or system intended to support or sustain life and/or health, which, if it fails, can be reasonably expected to result in significant personal injury or death. Silicon Laboratories products are generally not intended for military applications. Silicon Laboratories products shall under no circumstances be used in weapons of mass destruction including (but not limited to) nuclear, biological or chemical weapons, or missiles capable of delivering such weapons.

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