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Nat SM41 Installation And Operation Manual
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NPX138 Panel Mount Radio Manual SM41 Rev. 4.00Page 2-2 Nov 10, 2003ENG-FORM: 805-0104.DOT Amendment # 3 Nov 22, 2004PROPRIETARY AND CONFIDENTIAL TO NORTHERN AIRBORNE TECHNOLOGY LTD.2.3.3 NotesThe case of the NPX138 must be electrically grounded for maximum resistance to lowfrequency interference. A pin on the connector (Chassis ground) is provided and mustbe connected by a short wire to a clean ground, not jumpered to the power ground wireconnection.Refer to the aircraft structural repair manual and maintenance manual for instructionsand information pertinent to this installation.2.3.4 Cable and WiringAll unshielded wire shall be selected in accordance with AC43.13-1B Change 1,Paragraphs 11-76 through 11-78. Wire types should be to MIL-W-22759 as specified inAC43.13-1B Change 1, Paragraphs 11-85, 11-86, and listed in Table 11-11. Forshielded wire applications, use Tefzel MIL-C-27500 shielded wire with solder sleeves(for shield terminations) to make the most compact and easily terminated interconnect.Follow the wiring diagrams in Section 2.5 as required.Allow 3 inches from the end of the wire to the shield termination to allow the hood to beeasily installed. Note that the hood is installed after the wiring is complete.Installation cabling must allow the NPX138 to be easily withdrawn for disconnection andfield service adjustments. Ensure an adequate service loop in the routing of the cables.It can be a serious issue if the unit is installed with the cables so short that the unitcannot be removed without disassembly of the surrounding structures. At least 30 cm(1 foot) of free cable is recommended.All wiring should be 22 AWG minimum, except power and ground connections, whichmust be 20 AWG or larger, as indicated on the installation drawings. Ensure that theground connection is clean and well secured. To prevent inadvertent system failure,power to this system must be supplied from a separate breaker or fuse and notconnected to any other device. A 5 A fuse or breaker is recommended (28 Vdc).Coaxial cable should be in accordance with MIL-C-17 unless otherwise specified. Donot use coax with PVC insulation. Teflon dielectric cable is encouraged at or above VHFfrequencies or where cable runs exceed 8 feet. Note that at VHF frequencies, cable lossesdue to long cable runs and tight bends may cut the ERP (Equivalent Radiated Power) toless than 50% of spec.To prevent RF interference between similar systems, it is recommended that VHF FMcoax runs be widely separated, or be made using triaxial cable, with the outer shieldbonded to the airframe at one end only (transceiver end).In communication intensive applications, poor cable routing and shielding maydrastically compromise over-all system performance. Symptoms may be spurioussquelch opening, RFI (Radio-Frequency Interference), and garbled reception.RF cables must be neatly terminated (solder or crimp), and tested for shorts prior tosystem check-out (not while connected to the radio or antenna). Keep cable bends to a |
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