Frequency Offset Tuning; Testing Frequency Offset; Adjusting Frequency Offset - Espressif ESP8266 Matching Manual

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2.1. Testing Frequency Offset

The frequency offset can be tested in one of the following ways:
1. GPIO0 outputs crystal oscillator clock signals by default. Customers can compare the
calculated frequency against the standard frequency and get the offset value.
2. Customers can use AT command firmware and send AT + CWLAP command. The
last parameter is the offset value. However, it is a relative value. Customers can use a
standard device for comparison.
3. Customers can use FCC/CE test firmware to send standard wave and get the offset
value with IQView equipment. IQView equipment is as shown in Figure 2-1. FCC/CE
certification and test document can be downloaded from:
http://www.espressif.com/en/support/download/other-tools.
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2.2. Adjusting Frequency Offset

The frequency offset can be adjusted in two ways:
1. Adjust the regulating capacitors on both sides of crystal oscillator.
- Increase capacitance if the frequency offset is positive, for example +50 ppm.
- Decrease capacitance if the frequency offset is negative, for example -50 ppm.
- Generally, the capacitances should be matched and adjusted at the same time.
2. Modify the frequency offset in ESP8266 DOWNLOAD TOOL. Click LoadInitBin to
load esp_init_data_default.bin, modify PraticalFreqOffset and click GenInitBin to
generate a new esp_init_data_default.bin to download to Flash. Please refer to
Figure 2-2.
Espressif
Frequency Offset Tuning
Figure 2-1. IQView Equipment
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2. Frequency Offset Tuning

2016.06