S Meter Web

Current — dB rel S9

S Unit — S

Min — dB

Max — dB

Avg — dB

Update period:

Ruler: drag on chart to measure dB span (Ctrl+release to stamp) —

Scale:

0.0° Bearing (°): Auto

Idle

Statistics

Points 0

Peak bearing —

Peak signal —

Min signal —

Notes

Manual bearing — type the current antenna heading in the Bearing field before or during capture. Update it whenever you rotate the antenna and a new point will be plotted at that angle.

Auto mode — tick Auto and enter how fast your rotator turns in Degrees/sec (e.g. 3 °/s = full 360° rotation in 2 minutes). The bearing advances automatically in real-time based on elapsed time, so you just start the rotator and hit Start — no manual updates needed.

Each sample captured during the update period is averaged and plotted at the current bearing. Use CSV export for detailed post-processing.

Sample Log

Calibration Points — Raw value (0–255) → S-label & dB relative to S9

Raw (0–255)	S Label	dB (rel S9=0)

Values are linearly interpolated between points. S9 = 0 dB; each S-unit below S9 = −6 dB. Calibration is saved automatically and persists across sessions.

Serial Port (Web Serial API)

Click to open Chrome's port picker. Grant permission to proceed.

Baud Rate Stop Bits Parity

Radio Brand

Radio Model CI-V Address (hex)

CI-V command used: FE FE [addr] E0 15 02 FD · Response parsed: two BCD bytes, range 0–255

Connection Mode

Secure (wss:// via nginx/TLS) Local (ws://, no TLS)

Hostname

SDR: wss://<host>/ws/sdr · GPS: wss://<host>/ws/gps

Not connected

—

Center Frequency

MHz

Sample Rate Gain Mode

Automatic (AGC) Manual

Manual Gain Freq Correction

PPM

RTL2832U Digital AGC Enabled Reference Level

-30 dBFS

Stream Interval

Integration

Signal Stream

No data

GPS Stream Console log only — position display in a future update

Sampling & Update Rates

Sampling Rate Update Period

Update / Sample rate	4 Hz	8 Hz	12 Hz	20 Hz
2 s	8	16	24	40
1 s	4	8	12	20
0.5 s	2	4	6	10
0.25 s	1	2	3	5

Samples per update period averaged together.

Requirements

Browser: Chrome 89+ (or any Chromium-based browser) with Web Serial API and WebUSB API enabled.
Serial Connection: USB-to-serial adapter (FTDI, CP210x, CH340, etc.) or built-in USB-CAT interface.
ICOM: CI-V interface cable (CT-17 or equivalent). Set radio CI-V baud rate to match below.
Yaesu: CAT cable (SCU-17, CT-62, or equivalent). Enable CAT in radio menu.
RTL-SDR: RTL2832U-based USB dongle (dvb-t stick).
Windows 11 (RTL-SDR): Use Zadig to replace the default Realtek TV driver with WinUSB driver. Chrome will fail to claim the interface without this step.
Linux (RTL-SDR): Add udev rule: SUBSYSTEM=="usb", ATTRS{idVendor}=="0bda", MODE="0666" in /etc/udev/rules.d/99-rtlsdr.rules and reload: sudo udevadm control --reload-rules
Secure Context: WebUSB requires HTTPS or localhost. File:// protocol will not work for RTL-SDR.
Note: Only one application can hold the port/device open at a time.

Diagnostics — Raw Serial Monitor

Shows raw hex bytes TX (sent to radio) and RX (received from radio). Use this to confirm the radio is responding. Disable when not needed.

Diagnostics disabled. Click Enable to start logging.