SkyWalker Multi-Mode RF Tool

skywalker.py provides five alternative operating modes beyond satellite feed tuning. These modes repurpose the BCM4500’s AGC registers as a crude power detector across the 950—2150 MHz IF range, allowing spectrum sweeps, blind transponder scanning, real-time dish alignment, L-band direct input analysis, and carrier tracking — all without requiring demodulator lock.

Requires custom firmware v3.02.0+

Commands 0xB7 (SIGNAL_MONITOR), 0xB8 (TUNE_MONITOR), and 0xB9 (BLIND_SCAN) must be present in the FX2 firmware. See Custom v3.01 for the base firmware these commands build on.

Subcommands

Subcommand	Purpose
spectrum	Sweep spectrum analyzer (950—2150 MHz IF range)
scan	Automated transponder scanner (sweep + blind scan)
monitor	Real-time signal strength / dish alignment
lband	L-band direct input analyzer (no LNB)
track	Carrier/beacon tracker with logging

Global Options

Flag	Description
-v, --verbose	Show raw USB traffic

---

spectrum — Sweep Spectrum Analyzer

Sweeps the IF range using TUNE_MONITOR (0xB8) at each step and renders an ASCII bar chart to the terminal. Optionally produces waterfall displays, matplotlib plots, and CSV exports.

Options

Flag	Description
--start FLOAT	Start IF frequency in MHz (default: 950)
--stop FLOAT	Stop IF frequency in MHz (default: 2150)
--step FLOAT	Step size in MHz (default: 5)
--dwell INT	Dwell time per step in ms (default: 10)
--lnb-lo FLOAT	LNB LO frequency in MHz; 0 = direct input (default: 0)
--sr INT	Symbol rate for measurement in ksps (default: 20000)
--waterfall	Waterfall display (time x frequency x power)
--sweeps INT	Number of sweeps (default: 1)
--threshold FLOAT	Peak detection threshold in dB above noise floor (default: 3)
--plot	Show matplotlib plot after sweep completes
--csv FILE	Save sweep data to CSV

Examples

Full IF range sweep

sudo python3 tools/skywalker.py spectrum

Narrow sweep with LNB LO, save CSV

sudo python3 tools/skywalker.py spectrum --start 1200 --stop 1400 --step 2 --lnb-lo 9750 --csv sweep.csv

Waterfall display, 10 sweeps

sudo python3 tools/skywalker.py spectrum --waterfall --sweeps 10 --step 10

Plot with peak markers

sudo python3 tools/skywalker.py spectrum --plot --threshold 5

Sample Output

SkyWalker-1 Spectrum Sweep
==================================================
  Range:  950.0 - 2150.0 MHz IF  (step 5.0 MHz)
  Dwell:  10 ms/step   SR: 20000 ksps
  Steps:  240   Est. time: ~2.9s

 950.0 |                                     -62.3 dBm
 955.0 |                                     -61.8 dBm
 960.0 |                                     -62.1 dBm
  ...
1120.0 | ████████████████████                 -48.2 dBm
1125.0 | ██████████████████████████████████   -42.7 dBm  << PEAK
1130.0 | ████████████████████                 -48.5 dBm
  ...
1920.0 | █████████████████████████████        -44.1 dBm  << PEAK
1925.0 | ████████████████████████████████████ -41.3 dBm  << PEAK
1930.0 | ████████████████████████             -46.0 dBm
  ...
2145.0 |                                     -63.1 dBm
2150.0 |                                     -62.9 dBm

Peaks detected (>3.0 dB above floor):
  1125.0 MHz IF  -42.7 dBm  (RF: 1125.0 MHz)
  1925.0 MHz IF  -41.3 dBm  (RF: 1925.0 MHz)

Sweep complete: 240 steps in 2.88s

Tip

When --lnb-lo is set, the X-axis labels and peak report convert IF to RF using actual_rf = if_freq + lnb_lo. This makes it straightforward to identify transponders by their published downlink frequency.

Note

Sweep time scales linearly: 240 steps at 5 MHz spacing takes approximately 2.9 seconds (12 ms per step including USB overhead). Reduce --step for finer resolution at the cost of longer sweep times.

---

scan — Automated Transponder Scanner

Performs a three-phase automated transponder search: coarse spectrum sweep, fine sweep around detected peaks, and blind scan at each refined peak across a range of symbol rates.

Phases

1. Coarse sweep at 10 MHz steps across the full IF range to identify candidate carriers.
2. Fine sweep at 2 MHz steps around each peak detected in the coarse pass.
3. Blind scan (0xB3) at each refined peak, trying symbol rates from --sr-min to --sr-max in --sr-step increments.

Options

Flag	Description
--start FLOAT	Start IF frequency in MHz (default: 950)
--stop FLOAT	Stop IF frequency in MHz (default: 2150)
--threshold FLOAT	Peak detection threshold in dB (default: 3)
--sr-min INT	Minimum symbol rate in ksps (default: 1000)
--sr-max INT	Maximum symbol rate in ksps (default: 30000)
--sr-step INT	Symbol rate step in ksps (default: 500)
--lnb-lo FLOAT	LNB LO frequency in MHz (default: 9750)
--pol H/V/L/R	Polarization
--band low/high	LNB band
--json	JSON output
--csv FILE	CSV output

Examples

Full Ku-band low scan, horizontal

sudo python3 tools/skywalker.py scan --pol H --band low

Narrow scan, fast SR range, JSON output

sudo python3 tools/skywalker.py scan --start 1100 --stop 1200 --sr-min 10000 --sr-max 30000 --sr-step 1000 --json

C-band scan with custom LO

sudo python3 tools/skywalker.py scan --lnb-lo 5150 --pol V --csv cband_scan.csv

Caution

A full scan across the default frequency and symbol rate ranges can take several minutes. Narrowing --start/--stop or --sr-min/--sr-max significantly reduces scan time.

---

monitor — Real-Time Signal Strength

Tunes to a specified frequency and symbol rate, then polls SIGNAL_MONITOR (0xB7) at a configurable rate to display a continuously updating signal strength indicator. Designed for hands-free dish alignment.

Required Arguments

Argument	Description
FREQ_MHZ	Transponder frequency in MHz
SR_KSPS	Symbol rate in ksps

Options

Flag	Description
--pol H/V/L/R	Polarization
--band low/high	LNB band
--lnb-lo FLOAT	LNB LO frequency in MHz (default: 9750)
--rate FLOAT	Poll rate in Hz (default: 10, max ~50)
--audio	Pitch-proportional beep for hands-free alignment
--peak-hold	Track and display maximum signal level
--history INT	Sparkline history length in samples (default: 60)
--plot	Show matplotlib plot after stopping

Examples

Basic monitor, horizontal low-band

sudo python3 tools/skywalker.py monitor 12520 27500 --pol H --band high

Audio-assisted dish alignment

sudo python3 tools/skywalker.py monitor 11836 27500 --pol V --band low --audio --peak-hold

Fast polling with long history

sudo python3 tools/skywalker.py monitor 12520 27500 --pol H --band high --rate 30 --history 120

Display Format

[LOCK] SNR 8.2dB  AGC 0x3A  [████████████████░░░░░░░░░░░░░░░░░░░░░░░░] 42%  ▁▃▅▇█▇▅▃▅▇█▇▅▃▁
[----] SNR 0.0dB  AGC 0xFF  [░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░]  0%  ▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

The display updates in-place using terminal control codes. The sparkline at the right edge shows --history samples of recent signal strength. Press Ctrl-C to stop.

Tip

The --audio mode produces a tone whose pitch rises with signal strength. This frees you from watching the screen while adjusting the dish. Combine with --peak-hold to know when you have passed the optimum position.

Note

SIGNAL_MONITOR returns 8 bytes per read. Practical poll rates above 50 Hz are limited by USB round-trip latency, not the BCM4500.

---

lband — L-Band Direct Input Analyzer

Identical to spectrum mode but with lnb_lo=0 and LNB power disabled. Intended for direct RF input in the 950—2150 MHz range (L-band). Annotates known L-band frequency allocations in the output.

Options

Flag	Description
--start FLOAT	Start frequency in MHz (default: 950)
--stop FLOAT	Stop frequency in MHz (default: 2150)
--step FLOAT	Step size in MHz (default: 2)
--dwell INT	Dwell time per step in ms (default: 20)
--23cm	Narrow to 1240—1300 MHz with 500 kHz steps
--band-info	Print L-band allocation table and exit
--waterfall	Waterfall display
--plot	Show matplotlib plot
--csv FILE	Save data to CSV

L-Band Frequency Allocations

Range (MHz)	Service
1240—1300	Amateur 23cm
1525—1559	Inmarsat downlink
1559—1610	GNSS (GPS L1, Galileo E1)
1610—1626	Iridium downlink
1670—1710	MetSat (GOES LRIT, NOAA HRPT)
1710—1785	LTE/AWS uplink
1920—2025	UMTS uplink

Examples

Full L-band sweep

sudo python3 tools/skywalker.py lband

23cm amateur band, fine resolution

sudo python3 tools/skywalker.py lband --23cm

Waterfall with CSV export

sudo python3 tools/skywalker.py lband --waterfall --csv lband_sweep.csv

Print allocation table only

sudo python3 tools/skywalker.py lband --band-info

Caution

Can detect carrier presence at any frequency even if the modulation is incompatible with the BCM4500 demodulator. The AGC power reading does not depend on demodulation — only on RF energy at the tuned frequency. This makes L-band mode useful for detecting GNSS, Inmarsat, Iridium, and other signals that the BCM4500 cannot decode.

Tip

Connect an L-band antenna or filtered preamp directly to the SkyWalker-1’s F-type input. Do not power an LNB through this mode — LNB voltage output is explicitly disabled.

---

track — Carrier/Beacon Tracker

Tunes to a single frequency and symbol rate, then polls SIGNAL_MONITOR continuously with timestamped logging. Detects lock/unlock transitions and optionally tracks frequency drift by periodically sweeping a narrow window around the target.

Required Arguments

Argument	Description
FREQ_MHZ	Carrier frequency in MHz
SR_KSPS	Symbol rate in ksps

Options

Flag	Description
--pol H/V/L/R	Polarization
--band low/high	LNB band
--lnb-lo FLOAT	LNB LO frequency in MHz (default: 9750)
--rate FLOAT	Poll rate in Hz (default: 1)
--duration FLOAT	Duration in seconds (default: until Ctrl-C)
--log FILE	CSV log file
--drift-track	Sweep +/-5 MHz every 5s to measure frequency drift
--plot	Show matplotlib plot after stopping
--json-lines FILE	JSON-lines log file

Examples

Track a beacon for 1 hour, log to CSV

sudo python3 tools/skywalker.py track 11700 27500 --pol V --band low --duration 3600 --log beacon.csv

Drift tracking with JSON-lines output

sudo python3 tools/skywalker.py track 12520 27500 --pol H --band high --drift-track --json-lines drift.jsonl

Quick track with matplotlib plot on exit

sudo python3 tools/skywalker.py track 11836 27500 --pol V --band low --rate 5 --plot

Note

Lock/unlock transitions are detected and logged with timestamps. Each transition line in the CSV includes the previous state duration, making it straightforward to calculate uptime and outage windows.

Tip

The --drift-track option sweeps +/-5 MHz around the target frequency every 5 seconds. This is useful for characterizing LNB drift over temperature changes or for tracking satellites with measurable Doppler shift.

---

See Also

• Signal Monitoring — SIGNAL_MONITOR register protocol and data format
• Vendor Commands — complete USB vendor command reference including 0xB7—0xB9
• Tuning Tool — primary tuning, LNB control, and transport stream capture
• RF Coverage — frequency coverage and antenna considerations
• Spectrum Analysis How-to — practical guides for each operating mode