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
| Component | Part Number | Supplier | Notes |
|---|---|---|---|
| Audio panel | GMA 245 | Garmin | Bluetooth, IntelliVox |
| Com radio | GTN 650 Com | Garmin | Integrated in GTN 650 |
| Dynon Com panel | SV-COM-425 | Dynon | Com frequency control |
| Nav antenna | Bob Archer | Single nav antenna for GTN 650 | |
| Com antenna 1 | CI-121 | Comant | Top of fuselage |
| Com antenna 2 | CI-122 | Comant | Bottom of right wing |
| Intercom | GMA 245 internal | Garmin | 4-place |
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:
- 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.)
- 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
| Spec | CI-121 (top of fuselage) | CI-122 (bottom of right wing) |
|---|---|---|
| Frequency | 118–137 MHz | 118–137 MHz |
| VSWR | 2.5:1 max | 3.0:1 |
| Polarization | Vertical | Vertical |
| Pattern | Omnidirectional | Omnidirectional |
| Impedance | 50 Ω | 50 Ω |
| Power | 50 W | 50 W |
| Weight | 0.5 lb max | 0.5 lb max |
| Height | 18.50 in max | 8.75 in max |
| Material | Cast housing / fiberglass whip | Cast housing / stainless whip |
| Connector | BNC female | BNC |
| FAA TSO | C37d, C38d | C37d, C38d |
| Gasket | B12607-3 cork neoprene | C12607-3 cork neoprene |
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 — single nav antenna for GTN 650
Transponder & ADS-B Antennas
See also Navigation & Instruments.
| Spec | 104-12 Transponder | 104-17 ADS-B |
|---|---|---|
| Frequency | 1030–1090 MHz | 978 MHz |
| VSWR | 1.2:1 @ 1090 MHz, <2:1 @ 1030 MHz | — |
| Length | 3-1/8″ (79.4 mm) | 3-3/8″ (85.7 mm) |
| Weight | 0.053 lb | 0.053 lb |
| Connector | BNC female | BNC male |
| Mounting | O-ring sealed bulkhead feed-through | O-ring sealed bulkhead feed-through |
| Source | SteinAir | SteinAir |
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
| Parameter | Value |
|---|---|
| Model | SV-GPS-250/A |
| Type | Combined GPS receiver + antenna module |
| WAAS | Yes |
| Update rate | 5 Hz |
| Weight | 6.7 oz |
| Connections | 4 leads to SkyView DB37 via Serial Port 5 |
| Power | 8 VDC from SkyView DB37 pin 29 (GPS POWER OUT) |
| Ground | SkyView DB37 pin 24 (GPS GND) |
| Data TX | GPS gray/violet wire → DB37 pin 11 (Serial 5 RX) |
| Data RX | GPS gray/orange wire → DB37 pin 12 (Serial 5 TX) |
| Baud rate | 38,400 (SV-GPS-250); Serial Port 5 configured as POS 1 |
| Mounting | Overhead console |
| Used by | Dynon SkyView HDX |
Garmin GA 35
| Parameter | Value |
|---|---|
| Model | GA 35 |
| Part number | 013-00235-00 |
| Type | Passive GPS/WAAS antenna with built-in LNA |
| Frequency | 1575.42 MHz ±10 MHz (L1 GPS/WAAS) |
| Gain | 27+ dB at +25°C nominal |
| Impedance | 50 Ω |
| Connector | Female TNC |
| Supply current | 60 mA max |
| Weight | 0.47 lbs |
| Dimensions | 4.68 × 3.00 × 0.81 in |
| Mounting | 4x #8-32 oval head SS screws, 12–15 in-lbs torque |
| Certification | TSO-C144.9 |
| Mounting | Overhead console |
| Used by | Garmin GTN 650 |
ELT Antenna
| Parameter | Value |
|---|---|
| Model | ACR Artex 110-773 (Rev C) |
| Type | Dual-band whip antenna |
| Frequencies | 121.5 MHz and 406.0 MHz |
| Connector | BNC female |
| Speed rating | Fixed-wing up to 200 knots |
| Included with | Artex ELT 345 kit |
Antenna Summary
| Function | Antenna | Location |
|---|---|---|
| COM 1 | Comant CI-121 | Top of fuselage |
| COM 2 | Comant CI-122 | Bottom of right wing |
| NAV | Bob Archer | |
| Transponder | SteinAir 104-12 | |
| ADS-B | SteinAir 104-17 | |
| Dynon GPS | Dynon SV-GPS-250/A | Overhead console |
| GTN 650 GPS | Garmin GA 35 | Overhead console |
| ELT | ACR Artex 110-773 |
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:
| Signal | GTN 650 | GMA 245 | Wire |
|---|---|---|---|
| NAV audio (VOR/ILS ident) Hi | P1004-16 (VOR/ILS Audio Hi) | J1-17 (NAV 1 Audio Hi) | White |
| NAV audio (VOR/ILS ident) Lo | P1004-17 (VOR/ILS Audio Lo) | J1-18 (NAV 1 Lo) | White/Blue |
| GPS alert audio Hi (approach callouts, GTN tones) | P1001-4 (Audio Out Hi) | J1-31 (Alert 1 Audio Hi) | White |
| GPS alert audio Lo | P1001-23 (Audio Out Lo) | J1-32 (Alert 1 Audio Lo) | White/Blue |
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.
Inspection & Maintenance
References
- 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 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