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SN3308 Primary Navigation Display Support: Installation TipsThe SN3308 Primary Navigation Display is an extremely flexible and versatile instrument, and a well-planned installation is essential. This page describes the main areas of consideration when planning for an SN3308 Primary Navigation Display installation:
Heading InputThe SN3308 is a display device, intended to interface to multiple sensors. It does not contain a gyro or a compass, and must be connected to both an external remote gyro (either electric or vacuum) and to an external fluxgate compass. Examples of these items would be the Allied Signal (Bendix/King) KG102 Remote Gyro and the KMT112 Remote Fluxgate Compass. The Sandel SN3308 performs the slaving and compass calibration, so the KA-51 Slaving Accessory (normally installed as part of a KCS55 Compass System) is not required. Many other gyro/fluxgate combinations are also supported, such as those from Collins and Honeywell. Certain S-TEC gyros are compatible - please contact Sandel for specific information. Otherwise, the SN3308 is compatible with any standard XYZ synchro (ARINC 407) gyro. Another option is to retain an existing slaved mechanical HSI such as a KI-525A, Collins PN101 or Century NSD360 and use its output as a heading source for the Sandel SN3308. In this case, the old HSI can be either moved to the co-pilot's panel or perhaps installed as the NAV2 indicator. This approach is the most cost-effective, although adding an additional remote gyro and fluxgate would provide greater redundancy. NAV/GPS SwitchingThe SN3308 can control external NAV/GPS selectors such as an RS08-type relay box, but it does not do any analog switching internally. A single set of analog left/right, up/down and flag inputs is provided. This typically requires that an external relay be used to select between nav sources, and to provide a "selected" set of inputs that run in parallel to the SN3308 and to the aircraft's autopilot. See the illustration below:  NAV InterfacingWhile the SN3308 does have two different inputs for composite nav signals, these are used only for driving the RMI bearing pointers on the SN3308. The SN3308 does not contain a built-in nav converter, but does interface to virtually any external nav converter. The SN3308 presents a standard course resolver interface to the external nav converter, and receives analog left/right signals from it. In addition, the SN3308 receives vertical (glideslope) deviation signals directly from any standard glideslope receiver. Version 1.33 software, released on 5/19/99, introduced support for the differential resolvers used on the Collins VIR-30A and the Bendix/King KNR634 receivers. GPS/Loran InterfacingGPS and Loran receivers, known collectively as Long-Range Nav or LNAV, interface to the SN3308 using analog left/right/flag signals as well as a serial port for waypoint and navigation data. Analog signals are typically sent to the SN3308 via an external relay which allows the selection of NAV (VOR/LOC) or LNAV as the primary navigation source. The serial connection can be via RS232, RS422 or even ARINC 429. Supported serial formats include all major manufacturers: Garmin, Allied Signal (Bendix/King), II Morrow, Trimble, Northstar and Magellan. If it is available from your LNAV receiver, ARINC 429 is the recommended interface. ARINC 429 data received by the SN3308 includes, in addition to the normal nav info, the locations of the 100 nearest "off-route" waypoints and the status of all external annunciators. The waypoint data is used by the SN3308 to enhance the moving map display. The SN3308 also uses the ARINC 429 port to send "selected course" data to the LNAV receiver. This eliminates the need to switch the resolver lines through the external relay - no resolver connection is needed between the SN3308 and the LNAV if ARINC 429 is used. The SN3308 can legally replace the remote pushbutton/annunciator units required for some IFR GPSs. All remote annunciators are displayed right on the the SN3308's screen, using the color and nomenclature specified by each GPS manufacturer. Softkeys are provided for pushbutton functions such as ARM and OBS/HOLD. The SN3308 sends these signals directly to the GPS. GARMIN GNS 430 InterfacingThe GNS 430 is the first of a new generation of "all-in-one" NAV/GPS/COMM receivers. Sandel and GARMIN have jointly developed a complete ARINC 429 digital interface between the two products. A complete interface consists of four wires (two ARINC 429 pairs). This includes GPS waypoint, flightplan and nav data, VOR/LOC information, glideslope, resolver, and all flags and annunciators. No analog or discrete digital wiring is needed. Even NAV/GPS source selection is done over ARINC 429 - you can press either the NAV button on the SN3308 or the CDI button on the GNS 430 and both units will switch accordingly! A dual GNS 430 installation is slightly more involved. To have all four sources (NAV 1, GPS 1, NAV 2 and GPS 2) selectable on the SN3308 course pointer, a small relay must be installed to switch the ARINC 429 lines. Another alternative is to connect the #1 GNS 430 to the SN3308 with the four-wire interface described above, and connect the #2 GNS 430 to a standalone mechanical CDI such as the GARMIN GI 106 or the Bendix/King KI-206. This eliminates the need for any relays. In this configuration, the composite nav signal from the #2 GNS 430 can be connected to the SN3308 to provide an RMI bearing pointer to the #2 NAV. Either the GPS ARINC 429 or the RS-232 from the #2 GNS 430 can be connected to the SN3308 to provide an RMI bearing pointer to the #2 GPS, although this is not currently supported in the SN3308 software. A future software upgrade will support the selection of a #2 GPS bearing pointer, and it is recommended that the wiring be done now to allow this. A complete description of the SN3308 / GNS 430 interface is also available. See the Documentation section of this site for the GNS430-related drawings in the SN3308 Installation Manual. ADF InterfacingThe SN3308 can either supplement or replace the existing remote indicator on ADF receivers with a remote display head. The SN3308 accepts AC or DC sin/cosine inputs, as well as XYZ synchro (ARINC 407) inputs. DME InterfacingThe SN3308 accepts DME data in either "King serial digital" format as found on the KN62/KN64 and KN63, or in the older analog format of 40 millivolts per nautical mile. One or two DME receivers may be connected. If only one DME receiver is present, a "DME2 common" line can be used to signal the SN3308 that the NAV2 receiver is channeling the DME. The SN3308 will then display the DME data in the appropriate NAV2 data block. If a KN63 DME is interfaced to the SN3308, the KDI572 controller must also be retained. The KDI572 provides master timing signals to the KN63 and cannot be removed. Note that the SN3308 uses the same ports for both ARINC 429 and King serial digital DME data. With a single GNS430 connected, one input port remains available on the SN3308 for a DME input. With dual GNS430s both connected as primary nav sources, a digital DME such as the KN62 or KN63 cannot be interfaced. An older analog-style DME may still be interfaced in this situation, however. AutopilotsThe SN3308 can be configured to output either AC or DC signals for course datum and heading datum to the autopilot. These choices are made in the maintenance setup pages, where the course and heading datum signals can be made to emulate either a KI-525A, IN-832, Collins PN101 or a Century NSD360. These signals, along with vertical and horizontal deviation and flags, are typically connected directly to the autopilot. The SN3308 has demonstrated compatibility with King KFC150 and 200 systems, all current S-TEC systems, and Century I, II, III, IV and 2000 autopilots. Century autopilots such as the Century III using the 1C388 radio coupler will require the addition of a few small isolation transformers. See the installation documentation for details. Other EquipmentMarker BeaconsThe SN3308 accepts remote lamp driver outputs from virtually any marker beacon receiver. Outputs may be active high or active low, with a settable threshold. StormscopeThe WX-500 remote Stormscope sensor is the only weather detection device supported by the SN3308 at this time. All other models of Stormscope either do not output any electronic data, or output data in a format which is unusable by the SN3308. The WX-500 can receive its heading input from the SN3308's serial port. This eliminates the need to connect a heading bootstrap or a stepper motor interface to the WX-500. At a minimum, the WX-500 needs only power, ground, antenna, and RS232 Transmit and Receive lines to the SN3308. Required AccessoriesTwo panel-mounted accessories are required, and are included with the SN3308: a dimmer control and a dataload jack. The dimmer control is a 10K pot with a small diode, to be mounted in a convenient location near the SN3308. This pot generates a control voltage which adjusts the brightness - it does not function as a rheostat, so power dissipation is negligible. The dataload jack is a 1/4" phone jack, which can be mounted anywhere in the cockpit. The installer fabricates a mating cable which terminates in a DB9 connector. This allows connection to a standard PC serial comm port for software uploads and future database updates. Not SupportedAt this time, the following interfaces are not supported on the SN3308:
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