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Warning

This application is intended solely for experimental and educational purposes. Broadcasting GPS signals may be illegal in your jurisdiction and can interfere with navigation systems. You are solely responsible for ensuring compliance with all applicable laws before use.

GPS Sim replays pre-generated GPS baseband signal files (.C8 format) to simulate GPS satellite signals. It can be used to feed a fixed or moving position to GPS receivers for testing and research.

SD Card Setup

Place .C8 data files and their corresponding .TXT metadata files in the GPS/ directory at the root of the SD card. Both files must share the same base name (e.g. gpssim.C8 and gpssim.TXT).

When a .C8 file is opened, the app automatically reads the matching .TXT file and sets the transmit frequency and sample rate accordingly.

Metadata File Format

Create a .TXT file with the same name as the .C8 file containing:

center_frequency=1575420000
sample_rate=SAMPLE_RATE

center_frequency is the GPS L1 carrier frequency and should always be 1575420000. If the metadata file is missing, or if either value is zero, the app falls back to its defaults (1575.420 MHz, 2,600,000 Hz sample rate).

Known working sample rate values:

• 2600000
• 2500000
• 1250000

Generating C8 Files

Use the gps-sdr-sim tool to generate .C8 files. It requires a RINEX navigation file (GPS ephemeris data) as input.

Fixed position:

gps-sdr-sim -e BRDC_FILE.n -l LAT,LON,HEIGHT -b 8 -s 2600000 -o gpssim.C8

Moving position from NMEA file:

gps-sdr-sim -e BRDC_FILE.n -g NMEA_FILE.txt -b 8 -o gpssim.C8

RINEX navigation files (.n / .20n etc.) can be downloaded from public GNSS data archives such as NASA CDDIS or IGS. Use the file dated closest to your intended simulation date.

Example metadata file for the above:

center_frequency=1575420000
sample_rate=2600000

Controls

• Open file: Opens a file browser in GPS/, filtered to .C8 files. After selection, the filename, sample rate, and estimated duration are shown.
• Frequency / Gain / AMP: Transmit frequency, gain, and RF amplifier. Automatically set from the .TXT file when a capture is loaded.
• Loop (checkbox, default: on): When enabled, the file restarts automatically at end of file and transmits continuously.
• ▶ / ■: Start or stop transmission.

The progress bar shows playback position through the file. A live waterfall is displayed during transmission.

Default Transmission Parameters

Parameter	Default value
Frequency	1,575.420 MHz (GPS L1)
Bandwidth	15,000,000 Hz
Sample rate	2,600,000 Hz (overridden by .TXT file)

Improving Reception on Target Devices

Modern devices use multiple positioning sources and may reject spoofed GPS. To improve the chance of a lock:

• Enable airplane mode (disables Wi-Fi, Bluetooth, and cellular assisted positioning)
• Test indoors where real GPS signal is weak
• Reboot the device after enabling airplane mode

Known Device Results

Note

Newer devices increasingly use sensor fusion and network-based positioning. Results may vary by firmware version.

Type	Make	Model	Locks on spoofed GPS?	GPS acts "jammed"?	Notes
Tablet	Samsung	Note 7	No	Yes
Phone	Samsung	S8	Yes	No	Wi-Fi must be off
Phone	Huawei	P30 lite	No	Yes
Phone	Huawei	Mate 10 Pro	No	No	6–7 satellites: no fix
Smartwatch	Huawei	Amazfit Bip	Yes	No
Phone	Apple	iPhone 6	Yes	No	Works with Wi-Fi on
Phone	ZTE	Axon 7	Yes	No	Works with Wi-Fi on
Phone	Xiaomi	Mi5	Yes	No	Works with Wi-Fi on
Phone	Samsung	S20+ 4G	Yes	No	Wi-Fi must be off
Smartwatch	Samsung	Gear S3 WiFi	Yes	No	Location over GPS only
Phone	OnePlus	7 Pro	No	No	No effect observed
Phone	OnePlus	5	Yes	No	3D fix
Phone	Samsung	S21 Ultra	Yes	No

Settings Persistence

Settings are saved to tx_gps.ini.