Spectrum Analyzer
Spectrum Analyzer Guide
The spectrum analyzer is one of the most powerful features of the rfsplatter firmware. It shows you a real-time view of RF activity across a configurable frequency range, displayed as a bar graph with a squelch trigger line.
Opening the Spectrum Analyzer
F + 5Open the spectrum analyzer from normal operating mode.Side Key 2 (default)If Side Key 2 is programmed to Spectrum (factory default), press it to open the analyzer directly.Press EXIT to close the spectrum analyzer and return to normal operation.
Display Layout
- Spectrum bars — Each vertical bar represents the signal level (RSSI) at a specific frequency. Taller bars = stronger signal.
- Squelch trigger line — A horizontal line across the bar graph. Bars reaching or exceeding this line are considered active signals and can trigger the receiver. Controlled by the
*andFkeys. - Frequency markers — The current center frequency and bandwidth are shown at the bottom of the display. The active/cursor frequency is highlighted.
- Peak hold markers — Small dots or dashes showing the peak level reached at each frequency position since last cleared.
- Center frequency indicator — Shows the frequency at the center or at the cursor position.
Spectrum Analyzer Controls
| Key | Action | Details |
|---|---|---|
| UP arrow | Move cursor right (higher freq) | Moves the highlighted frequency position one step to the right |
| DOWN arrow | Move cursor left (lower freq) | Moves the highlighted frequency position one step to the left |
| 1 | Decrease step size | Zooms in — fewer kHz per bar. Smaller step = narrower view, more detail |
| 7 | Increase step size | Zooms out — more kHz per bar. Larger step = wider view, less detail |
| 2 | Decrease frequency | Shifts the entire spectrum view down in frequency |
| 8 | Increase frequency | Shifts the entire spectrum view up in frequency |
| 3 | Decrease squelch | Lowers the trigger line — opens squelch to weaker signals |
| 9 | Increase squelch | Raises the trigger line — requires stronger signal to trigger |
| 4 | Toggle steps count | Cycles through 16 / 32 / 64 / 128 bars. More bars = wider but slower scan |
| 5 | Frequency input | Opens direct frequency entry — type a frequency to jump the spectrum view there |
| 6 | Toggle bandwidth | Cycles through receiver bandwidth options (affects received audio on triggered frequency) |
| 0 | Toggle modulation | Cycles FM → AM → USB for the received audio when a signal triggers the squelch |
| * | Raise squelch line | Increases the trigger level (same as key 9 in some builds) |
| F | Lower squelch line | Decreases the trigger level (same as key 3 in some builds) |
| MENU | Tune to cursor frequency / enter STILL mode | Tune the active VFO to the current cursor frequency, or enter STILL mode register tuning |
| EXIT | Close spectrum analyzer | Returns to normal radio operation |
| Side Key 1 | Blacklist current peak | Marks the highest signal peak as blacklisted — excluded from triggering |
| PTT | Transmit | Transmit on the cursor frequency (use caution) |
Step Size — Zoom Level
The step size determines how much frequency each bar in the spectrum represents. Smaller steps give you a zoomed-in view; larger steps show a wider span.
| Step | Span (128 bars) | Best for |
|---|---|---|
| 2.5 kHz | 320 kHz | Narrow-band channel details |
| 5 kHz | 640 kHz | Typical amateur band segment |
| 10 kHz | 1.28 MHz | Multiple repeater pairs |
| 25 kHz | 3.2 MHz | Full VHF ham band (144–148 MHz) |
| 50 kHz | 6.4 MHz | Wide-band overview |
| 100 kHz | 12.8 MHz | Large frequency ranges |
Steps Count — Number of Bars
Press 4 to cycle through 16, 32, 64, and 128 bars. More bars give you a wider view at a given step size but update more slowly.
| Bars | Update rate | Tradeoff |
|---|---|---|
| 16 | Fastest | Narrow view, very responsive — good for watching a single channel |
| 32 | Fast | Good balance for most monitoring tasks |
| 64 | Medium | Wide view with reasonable update speed |
| 128 | Slowest | Widest view — best for initial band survey |
STILL Mode — Manual Register Tuning
STILL mode pauses the spectrum sweep and lets you manually adjust the radio's RF front-end registers (LNA, gain stages) for the currently displayed frequency. This is useful for optimizing sensitivity on a specific signal.
Entering STILL mode
- In the spectrum analyzer, position the cursor on a frequency of interest.
- Press
MENUto enter STILL mode. The spectrum sweep stops. - The display shows the current register values.
In STILL mode, use these controls:
| Key | Action |
|---|---|
| MENU | Cycle through registers: LNAs → LNA → PGA → IF |
| UP arrow | Increase current register value |
| DOWN arrow | Decrease current register value |
| EXIT | Exit STILL mode, return to sweep |
Register reference
- LNAs — Low Noise Amplifier (short) — first RF amplification stage. Higher values = more gain.
- LNA — Low Noise Amplifier — second LNA stage.
- PGA — Programmable Gain Amplifier — IF section gain.
- IF — Intermediate Frequency filter selection.
For very strong signals causing overload or audio distortion, reduce LNAs/LNA values. For weak signals in a quiet environment, try increasing them.
Blacklisting Interference Sources
Local interference or spurious signals may always appear tall in the spectrum, preventing the squelch trigger from working usefully.
Side Key 1Blacklist the current highest-strength signal peak. The blacklisted frequency is excluded from squelch triggering. This is session-only (not saved across power cycles).Scan Range Integration
When scan ranges are configured (via VFO A and VFO B as bounds), the spectrum analyzer can display only that defined frequency range. This is useful for staying focused on a specific band segment.
See the Scanning Guide for instructions on setting up scan ranges.
Tips for Effective Spectrum Analysis
- Start wide, then zoom in. Use 128 bars at 25–50 kHz/bar to survey a band, then switch to 32 bars at 2.5–5 kHz/bar for a specific channel area.
- Set step size to match channel spacing. For 12.5 kHz channel plans, use 12.5 kHz step for one channel per bar. For 25 kHz channels, use 25 kHz.
- Use the squelch line aggressively. Raise it until only real signals peek above. This makes triggering on noise impossible.
- Set modulation before opening the analyzer. The spectrum analyzer inherits the active VFO's modulation. You can toggle with key 0 inside the analyzer.
- Bandwidth matters for audio quality. Toggle bandwidth (key 6) if received audio sounds muffled (try Wide) or has adjacent-channel bleed (try Narrow).
- Blacklist local oscillator leakage. Some radios have their own internal spurs that appear in the spectrum. Blacklist them so they don't trigger the receiver.
- STILL mode for marginal signals. If you can barely hear a weak signal, enter STILL mode and carefully increase LNA values to boost sensitivity.