AN316 AM/FM TUNER FIELD TEST PROCEDURE. 1. Introduction. Table 1. AM/FM Tuner Field Test Equipment

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1 AM/FM TUNER FIELD TEST PROCEDURE 1. Introduction This document describes the recommended field test procedures for Silicon Laboratories AM/FM tuners. Field tests listed in this document exercise the tuners with radiated signals. It is beneficial to perform field tests since these 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. It should 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 Seek Performance IP3 Device Under Test Antenna(s) to be used with the DUT Image Rejection Rev /08 Copyright 2008 by Silicon Laboratories AN316

2 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. Do you recognize any sound? NO 0 YES Do you experience static >50% of the time? NO Can you generate static? NO 4 YES YES 3 Can you eliminate static? NO 1 YES 2 Figure 1. Channel Rating Flow Chart 2 Rev. 0.2

3 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 on your device, you can use another tuner with comparable performance as a benchmark device. During testing you will notice that even a small average rating difference between two devices translates into a significant difference in listening experience. To get a full list of stations available in a particular area, you can refer to websites that share radio location information. An example can be found at 3. Seek Performance Seek performance can be tested in different locations to verify performance under weak and strong signal environments. For weak performance area you can use a rural location, and for strong signal environment you can use an urban location. While conducting a seek performance test, make sure you have the same orientation for all antennas of the same type. 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 correct one, otherwise it might be an image or third order intermodulation product. See "FM Seek Performance Example" on page 6 for test results. Rev

4 4. IP3 In strong signal strength environments, intermodulation product of two strong channels might fall on top of a valid channel or can be detected as a station at a frequency that it's not intended to be transmitted. A good measure of intermodulation distortion is IP3. IP3 is the theoretical RF level at which two blockers offset from the desired frequency by f and 2 f, and their intermodulation product would be of the same amplitude. This test evaluates the IP3 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. 4 Rev. 0.2

5 APPENDIX EXAMPLES Introduction In 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 Competitive Si470x Solution #1 Solution # KNLE Candle KYCM 88.7 KAZI The Voice of Austin KMFA Voice of the Arts for Central Texas KTSW The Other Side of Radio 90.5 KUT National Public Radio KNCT 91.7 KOOP Austin Co-op Radio KQJZ K-Love 92.5 KKLB Club KDHT Hot KLBJ Austin s Rock Classic KAMX Mix KKMJ Majic KHFI 96.7 Kiss FM KVET 98.1 KVET KRXT Real Country KHHL Exitos KLGO The Word 99.7 KDHT Hot Pirate KASE Kase KROX 101-X KACQ KPEZ The River KBPA Bob FM KQBT The Beat KXXS Sol Música Romántica KMHF KFMK Jammin KQQT K-Love KXPW Power FM KHLB KGSR Radio Austin KINV La Recuerda KFAN Que Buena Channel Rating Total Total # Valid Stations Average Rating Rev

6 FM Seek Performance Example Legend: x: invalid seek. : valid seek; Frequency (MHz) Code Station Name Competitive Si470x Solution 88.1 KNLE Candle 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 x 93.3 KDHT Hot KLBJ Austin s Rock Classic 94.4 x 94.7 KAMX Mix x 95.5 KKMJ Majic 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 KLGO The Word 99.7 KDHT Hot Pirate x KASE Kase KROX 101-X KACQ x KPEZ The River Note: Stations in red are invalid stations that the devices reported during seek. 6 Rev. 0.2

7 Frequency (MHz) Code Station Name Competitive Solution x KBPA Bob FM 104 x KQBT The Beat KXXS Sol Música Romántica KMHF x KFMK Jammin KQQT K-Love KXPW Power FM x KHLB KGSR Radio Austin KINV La Recuerda KFAN Que Buena Total number of valid stations Total number of invalid stations 15 0 Note: Stations in red are invalid stations that the devices reported during seek. Si470x Rev

8 FM IP3 Example The table below shows all the strong stations from the channel rating example and their IP3 components. For simplicity, 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 at a 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 x x x x x x (2) x x x x x x x x x x x x x x x x (3) x x x x x x x x x x x (1) x (2) x (2) x Total # channels with intermodulation problems Rev. 0.2

9 FM Image Rejection Example AN316 The table below shows all the strong stations from the channel rating example. For simplicity, only stations with a rating of 4 have been chosen. Listening test checks whether the image frequency should be heard on these strong channels. 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 x x x x x Total # of channels where image frequency is audible 5 0 Rev

10 NOTES: 10 Rev. 0.2

11 DOCUMENT CHANGE LIST Revision 0.1 to 0.2 Added AM Receiver Information. Corrected information on Image Rejection definition. Rev

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