Introduction

FPV Detect is a PortaPack application for detecting analog FPV (first-person view) video signals and identifying their channel across the 5.8 GHz band. It covers all standard FPV bands — A, B, E, F, and R — used by most analog drone video transmitters (VTX) and goggles. The app can scan a single selected band or run AutoScan across all 40 channels simultaneously.

Its use is not limited to drone racing — it can be used to locate any analog FPV carrier in the 5.6–5.9 GHz range.

Controls

Top row:

• LNA: Low Noise Amplifier gain (0–40 dB).
• VGA: Variable Gain Amplifier / baseband gain (0–62 dB).
• AMP: RF preamplifier — 0 = off, 1 = on (+14 dB). Use with caution near strong signals.
• VOL: Audio output volume.

Second row:

• Band selector: Choose which band to scan — Band A, Band B, Band E, Band F, Band R, or AutoScan (default). AutoScan steps through all 5 bands × 8 channels = 40 channels in order.
• Frequency display: Shows the current channel being monitored in the format B3 5771 MHz (band letter, channel number, frequency).

Third row:

• State badge: Current detection state — SCANNING, VERIFY FPV, or DRONE FOUND (red when locked).
• Conf X%: Detection confidence percentage (0–99%). Increases during verification and lock.
• Thr> / threshold field: Detection threshold in dBm, adjustable from −100 to +20. Default: −38 dB. Only signals above this level trigger detection. Increase to reduce false positives in noisy environments; decrease if signals are weak.

Fourth row:

• RSSI min/avg/max: Scrolling RSSI bar graph (256 columns) showing min, average, and maximum received levels.
• PWR X dB: Current peak channel power in dB.

Status lines:

• Status text: Human-readable summary — band/channel/frequency when verifying or locked.
• Detail text: During scanning: shows the threshold requirement. During verification: shows average dB, peak dB, hit/sample counts. During lock: shows locked channel, confidence, and hold counter.

The lower part of the screen shows the scrolling RSSI history graph and a vertical peak-hold RSSI indicator on the right.

Detection algorithm

The app uses a three-state machine. The key insight is that a real FPV carrier is a narrow peak — it stands out clearly from adjacent channels. Broadband interference (Wi-Fi, noise) does not, so it gets filtered out during the neighbor check in the Candidate state.

stateDiagram-v2
    [*] --> Scanning

    Scanning --> Candidate : power ≥ threshold (default −38 dB)\nbeep 1150 Hz / 60 ms
    Candidate --> Locked : ≥4/5 hits AND conf ≥72%\nAND center ≥ neighbors+3 dB\nbeep 1850 Hz / 180 ms
    Candidate --> Scanning : verification failed\n(too few hits or weak neighbor margin)

    Locked --> Scanning : hold counter reaches 0\n(power stays below threshold−6 dB)\nbeep 650 Hz / 90 ms

    state Scanning {
        [*] --> stepping
        stepping --> stepping : 1 frame dwell per channel\nAutoscan: 40 ch total\nSingle band: 8 ch
    }

    state Candidate {
        [*] --> sampling
        sampling --> neighbor_check : after 2nd sample
        neighbor_check --> sampling : retune left+right neighbors\nto measure their power
        sampling --> lock_decision : 5 samples collected
    }

    state Locked {
        [*] --> holding
        holding --> holding : power ≥ threshold−6 dB\nhold counter stays at 12\nconf++ (up to 99%)
        holding --> draining : power < threshold−6 dB\nhold counter-- per frame
    }

Scanning — the receiver steps through channels one by one, dwelling for 1 frame per channel. When power exceeds the detection threshold, it enters Candidate.

Candidate — the app stays on the suspected channel and collects up to 5 power samples. After the 2nd sample it briefly re-tunes to the adjacent channels (left neighbor, then right neighbor) to measure their current power. A confidence score is computed from: average power above threshold, peak margin, hit/miss ratio, and neighbor margin (center power minus the strongest adjacent channel). Lock requires all three: ≥4 hits out of 5 samples, confidence ≥72%, and center channel at least 3 dB above neighbors. A fast-lock path fires earlier if peak exceeds threshold by ≥8 dB and confidence ≥80%.

Locked — the app stays on the confirmed channel, shows DRONE FOUND in red, and emits a long beep. A hold counter (max 12) prevents brief signal fades from unlocking immediately — each frame below the unlock threshold (= detection threshold − 6 dB) decrements the counter; unlock only occurs when it reaches zero.

FPV channel frequencies

All 40 standard channels covered by the app:

Ch	Band A (MHz)	Band B (MHz)	Band E (MHz)	Band F (MHz)	Band R (MHz)
1	5865	5733	5705	5740	5658
2	5845	5752	5685	5760	5695
3	5825	5771	5665	5780	5732
4	5805	5790	5645	5800	5769
5	5785	5809	5885	5820	5806
6	5765	5828	5905	5840	5843
7	5745	5847	5925	5860	5880
8	5725	5866	5945	5880	5917

The receive bandwidth is 750 kHz per channel (IQ capture mode, no audio demodulation during scanning).

Note: Band E channels 5–8 (5885–5945 MHz) and Band R channel 8 (5917 MHz) fall outside the standard 5.725–5.875 GHz ISM band. These are legal to receive but may not be legal to transmit on in all regions.

⚠️ False positives

FPV Detect can trigger false positives, particularly indoors or in urban environments where the 5.8 GHz band is crowded with non-FPV sources. Detection is based on signal power, not video content analysis — any sufficiently strong narrow emission near an FPV channel frequency can cause a lock. Common interference sources include Wi-Fi 5/6 routers (5.725–5.825 GHz overlap), ISM band devices (wireless cameras, baby monitors), wireless HDMI senders, and harmonic emissions from other transmitters.

If false locks occur frequently: raise the detection threshold, select a specific band instead of AutoScan, or move to an area with less RF congestion. When locked, the audio output lets you verify: an actual FPV analog video carrier produces a characteristic buzz, while interference typically sounds like noise or silence.

Settings persistence

The detection threshold value is saved automatically and restored on next launch. Settings are stored in SETTINGS/rx_fpv.ini on the SD card.e.