Transcript
AN316 AM/FM TU N E R F IELD TEST P ROCEDURE 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. 0.2 4/08
Copyright © 2008 by Silicon Laboratories
AN316
AN316 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?
YES
YES
3
Can you eliminate static?
NO
1
YES
2
Figure 1. Channel Rating Flow Chart
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Rev. 0.2
NO
4
AN316 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 http://www.radio-locator.com/
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. 0.2
3
AN316 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 2f, 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.
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Rev. 0.2
AN316 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 Solution #1 1
Competitive Solution #2 1
Si470x
88.1 88.5 88.7 89.5 89.9 90.5 91.3 91.7 92.1 92.5 93.3 93.7 94.7 95.5 96.7 98.1 98.5 98.9 99.3 99.7 100.1 100.7 101.5 101.9 102.3 103.5 104.3 104.9 105.1 105.9 106.3 106.7 106.9 107.1 107.7 107.9
KNLE KYCM KAZI KMFA KTSW KUT KNCT KOOP KQJZ KKLB KDHT KLBJ KAMX KKMJ KHFI KVET KRXT KHHL KLGO KDHT
Candle-88 The Voice of Austin Voice of the Arts for Central Texas The Other Side of Radio National Public Radio
4 4
4 3
4 4
3
3
3
Austin Co-op Radio K-Love Club 92.5 Hot 93.3 Austin’s Rock Classic Mix 94.7 Majic 95.5 96.7 Kiss FM 98.1 KVET Real Country Exitos 98.9 The Word Hot 99.7 Pirate Kase 101 101-X
3
4
4
3 3 4 4 3 3 4 2 3
2 2 3 3 3 3 4 2 3
3 3 4 4 4 4 4 2 4
1 1 4 4 0 4 3 2 4 0 4 1
1 1 3 4 2 4 3 1 3 1 4 1
1 2 3 4 0 4 4 1 3 0 4 1
4 2
4 1
4 1
78 28 2.78
73 28 2.61
79 28 2.82
KASE KROX KACQ KPEZ 102.3 The River KBPA Bob FM KQBT The Beat 104.3 KXXS Sol Música Romántica KMHF KFMK Jammin 105.9 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. 0.2
0
5
AN316 FM Seek Performance Example Legend: x: invalid seek.
: valid seek; Frequency (MHz)
Code
Station Name
88.1
KNLE
Candle-88
88.5
KYCM
Competitive Solution
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 94.7
x KAMX
Mix 94.7
95.4 95.5
x KKMJ
Majic 95.5
96
x
96.4
x KHFI
96.7 Kiss FM
98.1
KVET
98.1 KVET
98.5
KRXT
Real Country
96.7 97.6
x
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 102.3 The River
102.1 102.3
x KPEZ
Note: Stations in red are invalid stations that the devices reported during seek.
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Si470x
Rev. 0.2
AN316 Frequency (MHz)
Code
Station Name
Competitive Solution
102.7 103.5
Si470x
x 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
Note: Stations in red are invalid stations that the devices reported during seek.
Rev. 0.2
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AN316 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
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
6
0
Total # channels with intermodulation problems
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Rev. 0.2
AN316 FM Image Rejection Example 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
101.5
x
102.3
x
x
105.9
x
107.1
x
Total # of channels where image frequency is audible
5
0
Rev. 0.2
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AN316 NOTES:
10
Rev. 0.2
AN316 DOCUMENT CHANGE LIST Revision 0.1 to 0.2
Added AM Receiver Information. Corrected information on Image Rejection definition.
Rev. 0.2
11
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Disclaimer Silicon 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. Trademark Information Silicon Laboratories Inc., Silicon Laboratories, Silicon Labs, SiLabs and the Silicon Labs logo, CMEMS®, EFM, EFM32, EFR, Energy Micro, Energy Micro logo and combinations thereof, "the world’s most energy friendly microcontrollers", Ember®, EZLink®, EZMac®, EZRadio®, EZRadioPRO®, DSPLL®, ISOmodem ®, Precision32®, ProSLIC®, SiPHY®, USBXpress® and others are trademarks or registered trademarks of Silicon Laboratories Inc. ARM, CORTEX, Cortex-M3 and THUMB are trademarks or registered trademarks of ARM Holdings. Keil is a registered trademark of ARM Limited. All other products or brand names mentioned herein are trademarks of their respective holders.
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