Communications

ATA Chapter 23 — N720AK Systems Reference

Overview

N720AK’s communications stack includes the Garmin GMA 245 audio panel, Dynon Com Panel, and intercom system. The audio panel provides Bluetooth connectivity for phone calls and music.

Components

How It Works

NAV Audio (VOR/ILS Ident)

The GTN 650’s nav receiver audio (Morse ident for VOR/LOC identification) reaches the headsets through two gates in series — both must be open:

1. GTN 650: press the small right knob to activate the Nav window, then push the Volume knob to enable nav ident (an “ID” annunciation appears in the Nav window). Turning the Volume knob while the Nav window is active sets nav audio volume, independent of Com volume. (GTN 650 Pilot’s Guide §3.5.1.)
2. GMA 245: press the NAV1 key — nav receiver audio is heard only when its green in-key annunciator is lit. (GMA 245 Pilot’s Guide p. 15.)

The GTN also auto-decodes the Morse and displays the identifier next to the active nav frequency, but audible identification requires the chain above.

Related GMA 245 behaviors: the SPKR key routes selected radios to the cabin speaker (aural alerts always play on the speaker regardless); press-hold RADIO MUTE toggles intercom muting while radio (COM/NAV/AUX) audio is active.

Antennas

COM Antennas

The CI-121 is a straight vertical whip (standard Cessna-style). The CI-122 is a bent configuration designed for underside mounting.

All antenna coax is RG-400. See wing root connectors for the right wing COM antenna coax routing through the wing root CPC.

NAV Antenna

• Bob Archer (Sportcraft) — single wingtip nav antenna feeding the GTN 650. VOR, localizer and glideslope all come off this one antenna; the GTN’s glideslope diplexer is internal, so no external splitter is fitted.
• Mounted in the right wingtip. The coax reaches the panel through an inline BNC at the right wing root — see wing root connectors.

Grounding caveat specific to N720AK. Archer’s design grounds the antenna’s base strip by clamping it between the wingtip and the wing skin under the nutplate screws. N720AK’s wingtips are on piano hinges, so that path does not exist here. Anodized hinge stock is a poor RF conductor, and two RV-10 owners with hinge-mounted tips traced a wagging needle and a dead antenna to exactly this, both fixed with a strap from the base leg to the outboard rib. Verify the base leg reads under 1 Ω to the rib whenever the tip is off.

Known-good reference numbers for a stock Archer, from owners who measured: SWR under 2:1 across 108–118 MHz, and 4:1 to 6:1 at glideslope frequencies. The poor glideslope match is normal — Archer never designed for 330 MHz, and a GTN 650 works through it.

Diagnostics: plans/vor-antenna-diagnostic.md covers the RF interference survey, VNA measurement, and the antenna rebuild dimensions.

Transponder & ADS-B Antennas

See also Navigation & Instruments.

Both are non-TSO monopole antennas fed by 50 Ω RG-400 coax, with omnidirectional vertically-polarized radiation patterns.

GPS Antennas

Dynon SV-GPS-250/A

Garmin GA 35

• Installation Instructions (Rev F)

ELT Remote Switch

N720AK has a panel-mounted ELT remote switch (part of the Artex ELT 345 installation). It allows manual activation from the cockpit, so the beacon can be turned on before an off-airport landing instead of depending on the crash-activated g-switch.

This matters more than it looks: ELTs transmit after a crash only about half the time — some fail to activate, but more are separated from their antennas or buried. Activating while still airborne also gets the signal out from altitude.

The ELT Is GPS-Aided — Wiring

Confirmed from the SteinAir SkyView interconnect (SV_Interconnect.pdf, read off the drawing, 2026-09-14):

So the 406 MHz burst carries a GPS position rather than relying on Doppler resolution alone. That is worth more than it sounds: in the Embry-Riddle data cited by PilotWorkshops, mean search duration was 11.8 hours for a 406 ELT without GPS aiding against two hours with it.

Rest of the ELT DB15, same drawing:

The remote switch head wires to pins 3 and 14 (Wht/Blu and Wht/Ora).

Consequence for the position feed: the GPS data comes from the GTN, not from the ELT’s own receiver, so it is only as good as the GTN’s power and lock. In a total electrical failure the ELT still transmits on its internal battery, but without a live feed the position reverts to whatever it last had. One more reason the forced-landing checklists activate it early, while the panel is still up.

ELT Antenna

Antenna Summary

Wiring

GTN 650 → GMA 245 Audio Connections

Pin assignments traced on the SteinAir SkyView Interconnect schematic (verified visually end-to-end, 2026-08). Both runs are shielded twisted pairs with backshell-grounded shields:

The GMA 245’s NAV 2 input (J1-19/20) is unwired — the GTN is the only nav receiver. GTN nav audio and GTN alert audio arrive on separate audio panel inputs (NAV1 key vs. always-on alert input).

COM audio routing per the same drawing: GTN 650 com (P1003) is the GMA 245’s COM 1; the Dynon SV-COM C25 is COM 2.

Backup NavCom — Yaesu FTA-850 (handheld)

Carry-aboard backup transceiver (purchased 2026-08). COM 118–136.975 MHz transmit/receive, plus VOR and ILS CDI display on the NAV band (108–117.975) and a built-in GPS with waypoint/route navigation — so a total electrical failure still leaves com, a nav needle, and a position source. Nav functions are supplemental aids only, per Yaesu.

In the box (FTA-850L): SBR-39LI 7.2 V 2200 mAh lithium pack (~10 hr receive-heavy; 5.5 hr fast charge in the cradle), SAD-25 AC charger + SBH-11 cradle, SDD-12 cigarette-lighter DC adapter (12–24 V — runs off the panel power port), SCU-42 headset adapter cable (aviation headset → radio), SBT-12 alkaline AA tray (do NOT put rechargeables in it — no protection circuits), SRA-20A antenna, belt clip, USB cable.

Condensed operating guide

• 121.5 in one action: press and hold [121.5] — four beeps, tuned. Works even with the keypad locked. Exit: [COMM], confirm YES.
• Frequency entry: five keypad digits (134.35 → 1-3-4-3-5; trailing 5/0 of 8.33-style channels auto-completes), or the outer DIAL knob. [ENT] on the freq field recalls a recently-used list.
• Volume/squelch: inner knob = volume; hold SQL to open squelch for setting level against noise. Monitor switch un-mutes weak signals.
• Transmit: PTT on the left side; speak close to the grille mic (it’s waterproof-sealed and needs directed voice) — or use the SCU-42 with a real headset, which is the plan in the airplane.
• Memories: 400 channels in 9 groups. MENU → MEMORY → group → ▲/▼. [SAVE] from COMM mode stores the current freq. Bulk-load from a browser with the FTA-850 Memory Book Programmer (Chrome/Edge, USB, no driver) or Yaesu’s Windows-only YCE46 software — preload home/mission channels (KBDU, KBJC, KLMO, Denver App sectors, KEGE and mountain AWOS/CTAFs, Flight Service 122.2).
• VOR: tune a NAV-band VOR frequency and the CDI screen appears automatically — compass rose, deviation needle, TO/FROM, GPS speed-over-ground. Set the course: [FUNC] → OBS → enter the radial.
• ILS: tune the localizer frequency; LOC and GS needles display automatically. Combined with GPS groundspeed this is a genuine get-down-through-a-layer backup.
• Dual watch: polls a priority channel while listening to another (SETUP → COMM Setup sets the priority; FUNC menu toggles it).
• Weather: NOAA weather channels via MENU → WX; GPS position readout under the GPS menu for the “where am I” call.
• Battery discipline: battery-saver sleep cycles are on by default; the display battery icon blinks when charge is critical. AA tray rides in the flight bag as the deep reserve.

Carriage doctrine

• Lives charged and reachable from the pilot seat — not in the baggage area. The whole point is the panel-dark scenario.
• The SCU-42 headset adapter stays WITH the radio; using the internal mic/speaker against cabin noise at cruise is marginal.
• Rubber-duck antenna inside an aluminum cabin costs serious range — community consensus is roughly a factor of five versus an external antenna. Usable for pattern/tower work; for a real IFR lost-com the fix is an external antenna jack (BNC to a spare or belly whip) — candidate future wiring project.
• Exercised on a recurring schedule (flight-school sys-handheld-navcom drill): power on, recall a memory, hold [121.5], tune a VOR and set the OBS — so the first fumble happens on the ground.

Inspection & Maintenance

PC programming (YCE46) and the web programmer

Yaesu’s YCE46 (v1.0.0.0, 2021) is a .NET 4.6 WinForms program; its “driver” is just an INF binding the radio to Windows’ stock USB CDC-ACM serial driver (VID 26AA, PID 0024), so macOS and Linux need no driver at all. The radio must be in CP mode (hold SQL while powering on). The wire protocol is plain ASCII at 115200 8N1: tab-delimited commands with a one-byte XOR checksum (#CMDSY sync, #CVRRQ firmware version, #CEPSR status poll, #CEPRD/#CEPWR 64-byte reads and writes of a 32 KiB memory image), plus MediaTek PMTK sentences for the GPS logger. A .dat file is that raw image; model code 0352 sits at offsets 0x0100 and 0x7FFE, the 400 memory-book entries (48 bytes each) start at 0x3000, group names at 0x0300.

The web programmer in this handbook reimplements that protocol over Web Serial and edits only the memory-book areas. Source: sections/tools/fta850/; tests run with node --test tests/*.test.mjs against a fake radio. As of 2026-09 the write path has not yet been tried against the real radio.

References

• Yaesu FTA-850 Operating Manual
• Garmin GMA 245 Pilot’s Guide
• Garmin GTN 650 Pilot’s Guide
• Artex ELT 345 Manual
• Comant CI-121 Datasheet
• Comant CI-122 Datasheet
• Dynon SV-COM-425 Customer Drawing
• Bob Archer — Antennas for Aircraft
• Bob Archer — Wing Tip vs More Common Types of VOR Antennas
• AeroElectric Connection Fig. 13-12 — wingtip VOR antenna drawing (dimensions transcribed in plans/vor-antenna-diagnostic.md)
• Archer glideslope add-on — dimensioned PDF and Onshape CAD
• Bob Archer Antenna Installation Instructions
• Garmin GA 35 Installation Instructions (Rev F)
• Garmin GA 35 Product Page
• Dynon SV-GPS-250/A Product Page
• Dynon SkyView System Installation Guide
• ACR Artex 110-773 Whip Antenna
• Artex ELT 345 Manual