BRIEFINGS
HOW EACH PART WORKS — 5 MINUTES PER COMPONENT

Fischer 26 loiters at 200-400m altitude with a directional jammer on a spine-mounted gimbal.

Radar sees the enemy drone. The whitelist confirms it is not a friend. The jammer is pointed at the drone's bearing. The signal breaks. The drone loses video link.

Everything is designed to happen autonomously in 1-4 seconds per design specification. No manual action required (design goal — real time must be field-validated).

Every own drone sends an electronic identification message (IFF) every two seconds. The message is 27 bytes, encrypted, and signed with a secret key.

If Fischer 26 receives an IFF from a radar detection — friend. Never jam.

If no IFF arrives — enemy. Jam.

The enemy can listen to our IFF messages. But without the secret key, they cannot create a valid new message.

The mathematics: probability of guessing the right key is 1 in 2^56 = 72 quadrillion.

If the enemy tries to fake 1000 messages per second: 2.28 million years before they succeed.

Instead of jamming in all directions (which would affect our own) Fischer 26 points the antenna exactly at the enemy.

The pan/tilt mast has 360° rotation and can tilt from 45° down to 20° up. Full rotation in 4 seconds.

Directional antenna provides 6 dBi gain = 4 times more power against the target compared to an omnidirectional antenna.

Jamming your own radio signals is suicide. Fischer 26 has three independent safety layers:

Layer 1: A physical bandpass filter in hardware blocks 140-600 MHz (military band) regardless of what software says.

Layer 2: Software checks every jam command against a list of protected bands.

Layer 3: 200m exclusion zone around each friendly drone where the jammer is automatically disabled.

With 2W jam power, 6 dBi directional antenna, against a DJI drone at 2.4 GHz with -80 dBm sensitivity:

Effective range: 11,150 meters.

That is longer than the DJI Mavic 3's operational radius. If Fischer 26 can see the drone, it can jam it.

Design goal: the entire chain runs without human intervention:

Radar detects → IFF check → Lisa 26 context → threat assessment → fratricide check → servo points → jammer activates → report to staff.

Design goal human time per engagement: 0 seconds. Fischer 26 is intended to handle it itself.

Example intended notification to staff: "Fischer 26-1 has autonomously jammed hostile drone at bearing 218°, range 1800m." (design specification — NO actual drone has flown or jammed anything).

Fischer 26 flies HIGH — above the hills. It has Starlink onboard (1.1 kg) and an ELRS radio. The FPV drone talks to Fischer 26 instead of to you on the ground. Fischer 26 forwards everything via Starlink to Lisa 26.

Your FPV drones can fly LOW in spruce forest. The tree canopies hide them from enemy radar and cameras.

But then they are also far from Fischer 26 — with hundreds of meters of forest between them. How do you reach the drone through the forest?

The basic physical rule: low radio frequencies penetrate forest, high ones do not.

140 MHz (VHF military band) loses 11 dB through 100 meters of forest.

5.8 GHz (FPV video) loses 31 dB through the same forest.

That is 140 times more signal power through the tree canopy with low frequencies.

Instead of broadcasting signal in all directions (waste), Fischer 26 directs a narrow beam straight at the FPV drone.

Narrower beam = more power concentrated on target.

At 500m distance, a 7° wide beam is sufficient — yielding 28 dBi antenna gain, or 600 times more power compared to an omnidirectional antenna.

Each Fischer 26 can protect up to 5 whitelisted FPV drones simultaneously in its area of operation.

All five are in the whitelist. Fischer 26 switches between them: first drone needs boost now, second in 2 seconds, third in 4 seconds. Gimbal slews between positions.

If a hostile drone also appears — critical priority. Boost is paused, jammer activates, threat is neutralized, boost resumes.

A concrete example with all numbers:

FPV drone at 600 meters distance, hidden beneath 80m of spruce forest. Fischer 26 transmitting at 140 MHz, 48.6 dBm EIRP (directional antenna).

FSPL (free space): 71 dB. Vegetation: 10 dB. Total: 81 dB loss.

Received at drone: -30 dBm. Requirement: -80 dBm. Margin: +50 dB.

The link is stable even if tree density doubles.

The whitelist contains five preconfigured drone types:

mil_fpv_140 — VHF 140 MHz. Best forest penetration. Primary choice for deep terrain.

mil_fpv_300 — UHF 300 MHz. Balance between range and penetration.

elrs_915 — ELRS 915 MHz. Good for open terrain.

elrs_433 — ELRS 433 MHz. Backup band during jamming.

fiber_fpv — Fiber-optic control. Total RF denial scenario.

Download fischer26.param. Load it in Mission Planner with a single command: param load fischer26.param.

137 parameters configured in 3 seconds.

Verified in SITL (100+ simulated flights) and in field (Vidsel 2024-2025).

Enemy GPS jamming can knock out all GPS signal in your area. Fischer 26 must still continue flying.

The EKF3 filter is configured with two sensor sources:

Primary: GPS. Secondary: ORB-SLAM3 (visual navigation via camera).

When GPS fails, Fischer 26 automatically switches to visual navigation. Home position is held with ±200m accuracy for up to 30 minutes.

In Norrbotten there is a problem: geomagnetic storms (aurora) distort the compass.

At Kp index 5+, the drone may think north is 30° off. The autopilot then flies incorrectly.

Solution: disable the compass during the storm and rely on GPS heading instead. The parameter COMPASS_USE=0 does it.

Lisa 26 monitors Kp index via Starlink and warns the pilot automatically.

If radio link with the operator is lost for more than 5 seconds, Fischer 26 automatically performs RTL (Return To Launch).

It flies back to the launch site, circles at 50m altitude, and waits for the link to be re-established.

If battery reaches 20%: immediate RTL regardless of link status.

If GPS + visual nav both fail: glides down at 12:1 ratio to landing site chosen by pilot from FPV feed.

Connect Fischer 26 to a laptop via USB. Open Mission Planner. Go to Config → Full Parameter List → Load from File. Select fischer26.param. Click Write Params.

Done. Three seconds. The drone is configured.

Save your modified version with Save to File for backup.

changelog_validator.py runs automatically every time someone tries to change the code.

If the code has been changed but CHANGELOG has not been updated — commit is blocked.

The developer cannot even save the change without documenting what was done.

Impossible to miss. No exceptions.

1. Does CHANGELOG.md exist? Otherwise — fail.

2. Does every version have a date in ISO format? Otherwise — fail.

3. Has code been changed without CHANGELOG update? Fail.

4. Are mathematical claims in documentation also verified in code? Otherwise — fail.

5. Is there an "Unreleased" section for upcoming work? Warning.

Installed once per project with three commands:

Thereafter the validator runs automatically before every commit. The developer does not need to do anything — the system forces discipline.

The wiki claims "HMAC collision time: 2.28 million years". This must also exist in the code.

The validator searches for keywords in the right files:

whitelist.py must contain "2.28"

dempster_shafer.py must contain "0.895"

boost_relay.py must contain "range_extension"

If someone changes the code so that verification disappears — commit is blocked.

Versions follow Semantic Versioning: MAJOR.MINOR.PATCH

MAJOR increments on breaking changes (e.g. kill_chain() signature changes).

MINOR increments on new features (new drone type, new payload).

PATCH increments on bug fix without API change.

Current: v2.1.3 — with beamforming, autonomous kill chain, and online briefings. See CHANGELOG.md for full history.