Nat 246 Installation And Operation Manual
The Nat 246 Isolation Amplifier is a high-quality audio device designed to enhance your aviation experience. With its ability to drive 100 mWrms into a 600 Ohm load and 5 Wrms into an 8 Ohm load, it delivers crystal-clear audio output. The internal gain adjustment feature allows you to customize the sound level to your preference, ranging from 4.5 dB to 42 dB. Enjoy distortion-free audio even at high volumes, thanks to its low distortion rate of less than 1%. The Nat 246 also features a built-in microphone bias of 15 Vdc at 30 ±5 mA, making it compatible with a wide range of microphones.
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Installation and Operation Manual
Model 246
Isolation Amplifier
SM246
ISSUE 2.00
Northern Airborne Technology Ltd.
1925 Kirschner Road
Kelowna, BC, Canada.
V1Y 4N7
Telephone (250) 763-2232
Facsimile (250) 762-3374
Issued on the authority of Northern Airborne Technology Ltd.
Copyright 1996
Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Northern Airborne Technology Ltd.
has acquired the assets of dB Systems Inc., and has revised and reissued this manual in standard NAT format.
Northern Airborne Technology Ltd.
will be responsible for all future amendments and revisions.
Installation and Operation Manual
ENG-FORM: 820-0114.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
Page ii
Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Table of Contents
Section Title
1. Description
1.1 Introduction
1.3
1.4
1.4.1
1.4.2
1.4.3
1.4.3
Design Features
Specifications
Electrical Specifications
Physical Specifications
Environmental Specifications
Product Approval
2. Installation
2.1 Introduction
2.2 Unpacking and Inspection
2.2.1 Warranty
2.3 Continued Airworthiness
2.4
2.4.1
2.4.2
2.4.3
2.4.4
2.4.5
2.4.6
2.4.7
Installation Procedures
Warnings
Cautions
Cabling and Wiring
Pin Identification
Beech/King Air Interphone Interconnect
Typical Collins Interconnect
Post Installation Checks
2.5
2.5.1
2.5.2
2.6
2.7
Adjustments and Connections
Mechanical Installation
Adjustments
Accessories Required But Not Supplied
Installation Drawings
3. Operation
3.1 Introduction
Page
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2-2
2-3
2-4
2-5
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2-5
2-6
2-6
2-1
2-1
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Installation and Operation Manual
ENG-FORM: 820-0114.DOT
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CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Section 1 Description
1.1 Introduction
Information in this section consists of product description, design features and specifications for the
Model 246 Isolation Amplifier. All derivative product information shall be contained in the applicable manual supplement, which may be obtained from NAT as required.
Review all notes, warnings and cautions.
1.2 Product Description
The Model 246 Isolation Amplifier is an electronic device capable of driving 100 mWrms into a
600 Ohm load. It is intended as a direct replacement for the Collins model 356C-4. The Model 246 is also capable of driving 5 Wrms into an 8 Ohm load.
1.3 Design Features
The Model 246 Isolation Amplifier is based on a solid-state integrated circuit. It has a 470 Ohm differential input and an output compatible with a 600 Ohm or a 4 Ohm load. It provides an internal gain adjustment (accessible through a hole in the cover) of 4.5 dB to 42 dB and is capable of supplying a minimum of 100 mW into a 600 Ohm load. It will drive headphones with impedance ratings of 4 to 600 ohms. With the unit adjusted for a gain of 40 dB, an input level of 77.5 mVrms will produce an output level of 7.75 Vrms (100 mW into 600 ohms.)
1.4 Specifications
1.4.1 Electrical Specifications
Input
Output
Microphone Bias
Output Noise
Power Supply
0.0775 Vrms into 470 ohms
100 mWrms into 600 ohms at <1 % distortion
15 Vdc at 30 ± 5 mA (enabled by internal jumper)
70 dB below 100 mW
<0.5 amp at 28 Vdc, 1 A circuit breaker recommended
1.4.2
Height
Depth
Width
Weight
Physical Specifications
1.53" (38.86 mm) max
2.81" (71.37 mm) max including flanges
2.78" (70.61 mm) max excluding connector
0.35 lbs (159 g)
Section 1 Rev: 1.00
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CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
1.4.3 Environmental Specifications
Temperature -55
°
C to +70
°
C
Altitude
Qualification of the Model 246 Isolation Amplifier was completed in accordance with
RTCA/DO-160C Environmental Categories: [A2F2]-BA[CL]XXXXXXZ[BZ]AAATZ[XXC2]XX
Note : Refer to Environmental Qualification Form located in Section 2 of this Manual for complete details of the environmental categories.
FAA: TSO-C50c (RTCA/DO-214, RTCA/DO-160C)
Section 1 ends
Section 1 Rev: 1.00
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CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Section 2 Installation
2.1 Introduction
Information in this section consists of unpacking and inspection procedures, installation procedures, postinstallation checks and installation drawings for the Model 246 Isolation Amplifier.
Review all notes, warnings and cautions.
2.2 Unpacking and Inspection
Unpack the equipment carefully and locate the warranty card. Inspect the unit visually for damage due to shipping and report all such claims immediately to the carrier involved. Check that all items listed below are present before proceeding and report any shortage immediately to your supplier:
- Warranty Card
- Certificate of Conformity or Release Certification
2.2.1 Warranty
All Northern Airborne Technology Ltd. products are warranted for 2 years from date of installation by an authorized NAT dealer, to be free of defects in workmanship or performance. This warranty covers all materials and labour, but is exclusive of any transport to deliver the defective unit to and from NAT or its designated warranty repair center, or any labour to remove or re-install the defective unit in the aircraft.
Contact NAT for any questions regarding this warranty, its applicability to your units and/or for return authorization. NAT is the final arbitrator concerning warranty administration. Units which have been physically damaged, burned, immersed in water or otherwise abused beyond the scope of normal use will not be considered for warranty. WARRANTY IS VOID UNLESS THE PRODUCT IS INSTALLED BY AN
AUTHORIZED NAT DEALER . Product for which a warranty card is not returned shall be warranted from date of manufacture.
2.3 Continued Airworthiness
Maintenance of the Model 246 Isolation Amplifier is ‘on condition’ only. Periodic maintenance of this product is not required.
2.4 Installation Procedures
2.4.1 Warnings
WARNING:
High volume settings can cause hearing damage.
Set the headset volume control to the minimum volume setting prior to conducting tests, and slowly increase the headset volume to a comfortable listening level.
Section 2 Rev: 1.00
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CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
2.4.2 Cautions
Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
CAUTION:
In all installations, use shielded cable exactly as shown, and ground only as indicated. Significant problems may result from not following these guidelines.
Failure to follow the installation and wiring instructions provided in this manual for power and ground connections, including the rating of the circuit breaker, may lead to damage in the power input circuitry of the unit.
2.4.3 Cabling and Wiring
All wire shall be selected in accordance with the original aircraft manufacturer's Maintenance Instructions or AC43.13-1B Change 1, Paragraphs 11-76 through 11-78. Unshielded wire types shall qualify to
MIL-W-22759 as specified in AC43.13-1B Change 1, Paragraphs 11-85, 11-86, and listed in Table 11-11.
For shielded 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 connector map in
Section 2.7 as required.
Allow 3" from the end of the shielded wiring to the shield termination to allow the connector hood to be easily installed. Reference the interconnect drawing in Section 2.7 for shield termination details.
Maintain wire segregation and route wiring in accordance with the original aircraft manufacturer's
Maintenance Instructions.
The input pins (A, B, and C) should be wired using 22 to 24 AWG shielded cable. The shield is attached to the airframe at one end only.
The output pins (D and E) and power pins (F and G) should be wired using wire no smaller than 20 AWG.
Reference the Interconnect drawings for additional specifications. Check that the ground connection is clean and well secured, and that it shares no path with any electrically noisy aircraft accessories such as blowers, turn and bank instruments or similar loads. Power to this unit must be supplied from a separate circuit breaker or fuse (fast blow), and not attached to any other circuit breaker without additional protection. Verify that the selected circuit breaker size and wire gauge are adequate for the installation using the techniques specified in AC43.13-1B Change 1, Paragraphs 11-47 through 11-51 and 11-66 through 11-69.
2.4.4 Pin Identification
The table below shows the pin identifications for the 7-pin connector:
Pin Number Function Pin Number Function
A
B
C
+ Signal input
Signal ground
- Signal input
E
F
G
+ Output
Power ground
+ 28 VDC IN
Phasing: Output pin E is in phase with input pin A and 180 degrees out of phase with input pin C.
Section 2 Rev: 1.00
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CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
2.4.5
Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Beech/King Air Interphone Interconnect
Section 2 Rev: 1.00
ENG-FORM: 805-0115.DOT
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CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
2.4.6
Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Typical Collins Interconnect
Section 2 Rev: 1.00
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CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Post Installation Checks 2.4.7
If any preset requires adjustment, be sure this is carried out before the aircraft leaves, and that the unit and its mating connector are secured before departure. Make all required log book entries, electrical load, weight and balance amendments and other paperwork as required by your local regulatory agency.
2.4.7.1 Voltage/Resistance Checks
Do not attach the Model 246 until the following conditions are met.
Check the following: pin for +28 Vdc relative to ground. pin for continuity to ground (less than 0.5 Ω ).
2.4.7.2 Power On Checks
WARNING:
High volume settings can cause hearing damage .
Set the headset volume control to the minimum volume setting prior to conducting audio tests, and slowly increase the headset volume level to a comfortable listening level.
Power up the aircraft’s systems and verify normal operation of all functions of the model 246.
Upon satisfactory completion of all performance checks, make all required log book entries, electrical load, weight and balance amendments and other documentation as required by your local regulatory agency before releasing the aircraft for service.
2.5 Adjustments and Connections
2.5.1 Mechanical Installation
The Model 246 may be mounted and operated in any position; however, access to the gain adjustment should be considered. The amplifier chassis must be electrically bonded to the airframe. The finish on the chassis is electrically conductive and need not be removed for electrical bonding. If the Model 246 will be driving more than approximately 2 Watts into a load, it is recommended that the unit be mounted on a metal surface of no less than 100 square inches.
2.5.2 Adjustments
2.5.2.1 Internal Gain Adjustment
The Model 246 has an internal gain adjustment, accessible through an opening in the cover.
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CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Jumper Adjustments 2.5.2.1
Access to the jumper is by cover removal. Refer to Assembly drawing 246-1 in the SM246 Maintenance manual. To remove the Model 246 cover, remove the 4 screws in the sides of the unit (do not remove screws under the base of the unit). Lift the cover to remove. Reinstall the cover by following the same steps in reverse order. Tighten all screws securely but do not over-tighten.
CAUTION
The Model 246 Series Isolation Amplifier contains static sensitive devices. Proper ESD handling procedures must be followed to prevent damage to the unit.
An internal jumper J1 allows the installer to apply a 30 mA microphone bias current to pins A and C. The microphone may be connected between pins A and B or pins C and B. This makes the Model 246 compatible with the Model 210 Voice Activated Switch.
Note : The Collins unit provides only 5 mA bias current.
When jumper J1 is connected between P2 pins 1 and 2 (closest to connector), the microphone bias current is enabled. When it is connected between pins 2 and 3 (furthest from the connector), it is disabled.
2.6 Accessories Required But Not Supplied
To complete the installation, a 246-IKC crimp Installation kit, NAT Part # C16S-1-IKC , is required. The kit consists of the following:
NAT Part #: C16S-1-IKC
Quantity Description NAT Part #
1 Circular Socket, Crimp, Bulkhead 20-33-944
2.7 Installation Drawings
246
246\246\521-0 1.00 Isolation Amplifier
Outline
Environmental Qual Form
Section 2 ends following the above documents
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Conditions Section Description of Conducted Tests
Power input
Voltage spike
Audio frequency conducted susceptibility
Induced signal susceptibility
Radio frequency susceptibility
16.0
17.0
18.0
19.0
20.0
Change No. 3
Categories B and Z
• Emergency operating voltage was tested
Category A
Category A
Category A
Category T
Emission of radio frequency energy
Lightning induced transient susceptibility
Lightning direct effect
22.0
Change No. 2
23.0
Category XXC2
Category X, no test required
Icing 24.0 Category X, no test required
REMARKS :
- Tests of DO-160C, Sections 6.0, 7.0 and 8.0 were conducted at Northern Airborne
Technology Ltd. (NAT) in Kelowna, BC on Model 246.
- Tests of DO-160C, Sections 16.0 and 18.0 were conducted at dB Systems, Inc. in
Redmond, WA on Model 246.
- Tests of DO-160C, Sections 4.0 (paragraphs 4.5.1, 4.5.2, & 4.5.3) and 5.0 were conducted at dB Systems, Inc. in Redmond, WA on Model 245.
- Tests of DO-160C, Sections 4.0 (paragraphs 4.6.1, 4.6.2, 4.6.3), 15.0, 17.0, 19.0,
20.0, 21.0, and 22.0 were conducted at Allied Signal Aerospace, Inc. in Redmond,
WA, on Model 245.
- Model 246-[ ] meets the requirements of RTCA DO-160C sections 4.0, 5.0, 15.0,
17.0, 19.0, 20.0, 21.0, and 22.0 by similarity to Model 245-[ ].
End of Environmental Qualification Form
Rev: 1.00 Jun 17, 2008 Page 2 of 2
ENG-FORM: 521-0102.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Section 3 Operation
3.1 Introduction
Information in this section consists of the functional and operational procedures for the Model 246 Isolation
Amplifier.
3.2 General Information
The Model 246 Isolation Amplifier is an electronic device capable of driving 100 mWrms into a
600 Ohm load. It is intended as a direct replacement for the Collins model 356C-4. The Model 246 is also capable of driving 5 Watts RMS into an 8 Ohm load.
The Model 246 Isolation Amplifier has no operator accessible controls. During installation, it may be determined that level adjustments are required. Qualified personnel only shall complete level adjustments.
Section 3 ends
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CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.

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