Nat 246 User manual

Northern Airborne Technology Ltd.
1925 Kirschner Road
Kelowna, BC, Canada.
V1Y 4N7
Telephone [phone]
Facsimile [phone]
Issued on the authority of Northern Airborne Technology Ltd.
Copyright 1996
Installation and Operation Manual
Model 246
Isolation Amplifier
SM246
ISSUE 2.00

Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Installation and Operation Manual Page ii
ENG-FORM: 820-0114.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
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.

Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Installation and Operation Manual Page iv
ENG-FORM: 820-0114.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
Table of Contents
Section Title Page
1. Description
1.1 Introduction 1-1
1.2 Product Description 1-1
1.3 Design Features 1-1
1.4 Specifications 1-1
1.4.1 Electrical Specifications 1-1
1.4.2 Physical Specifications 1-1
1.4.3 Environmental Specifications 1-2
1.4.3 Product Approval 1-2
2. Installation
2.1 Introduction 2-1
2.2 Unpacking and Inspection 2-1
2.2.1 Warranty 2-1
2.3 Continued Airworthiness 2-1
2.4 Installation Procedures 2-1
2.4.1 Warnings 2-1
2.4.2 Cautions 2-2
2.4.3 Cabling and Wiring 2-2
2.4.4 Pin Identification 2-2
2.4.5 Beech/King Air Interphone Interconnect 2-3
2.4.6 Typical Collins Interconnect 2-4
2.4.7 Post Installation Checks 2-5
2.5 Adjustments and Connections 2-5
2.5.1 Mechanical Installation 2-5
2.5.2 Adjustments 2-5
2.6 Accessories Required But Not Supplied 2-6
2.7 Installation Drawings 2-6
3. Operation
3.1 Introduction 3-1
3.2 General Information 3-1

Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Section 1 Rev: 1.00 Issue 2 Page 1-1
ENG-FORM: 800-0113.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
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 0.0775 Vrms into 470 ohms
Output 100 mWrms into 600 ohms at <1 % distortion
Microphone Bias 15 Vdc at 30 ±5 mA (enabled by internal jumper)
Output Noise 70 dB below 100 mW
Power Supply <0.5 amp at 28 Vdc, 1 A circuit breaker recommended
1.4.2 Physical Specifications
Height 1.53" (38.86 mm) max
Depth 2.81" (71.37 mm) max including flanges
Width 2.78" (70.61 mm) max excluding connector
Weight 0.35 lbs (159 g)

Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Section 1 Rev: 1.00 Issue 2 Page 1-2
ENG-FORM: 800-0113.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
1.4.3 Environmental Specifications
Temperature -55°C to +70°C
Altitude 70,000 ft
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.
1.4.4 Product Approval
FAA: TSO-C50c (RTCA/DO-214, RTCA/DO-160C)
Section 1 ends

Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Section 2 Rev: 1.00 Issue 2 Page 2-1
ENG-FORM: 805-0115.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
Section 2 Installation
2.1 Introduction
Information in this section consists of unpacking and inspection procedures, installation procedures, post-
installation 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.

Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Section 2 Rev: 1.00 Issue 2 Page 2-2
ENG-FORM: 805-0115.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
2.4.2 Cautions
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 + Signal input E + Output
B Signal ground F Power ground
C - Signal input G + 28 VDC IN
D Output ground
Phasing: Output pin E is in phase with input pin A and 180 degrees out of phase with input pin C.

Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Section 2 Rev: 1.00 Issue 2 Page 2-3
2.4.5 Beech/King Air Interphone Interconnect
ENG-FORM: 805-0115.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.

Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Section 2 Rev: 1.00 Issue 2 Page 2-4
2.4.6 Typical Collins Interconnect
ENG-FORM: 805-0115.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.

Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Section 2 Rev: 1.00 Issue 2 Page 2-5
ENG-FORM: 805-0115.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
2.4.7 Post Installation Checks
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:
a) Check pin <G> for +28 Vdc relative to ground.
b) Check pin <F> 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.

Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Section 2 Rev: 1.00 Issue 2 Page 2-6
2.5.2.1 Jumper Adjustments
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.
Pin 3 Pin 2 Pin 1
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
DRAWING REV. DESCRIPTION TYPE SERIAL No.
246
246\246\246 1.41 Isolation Amplifier Outline All
246\246\521-0 1.00 Isolation Amplifier Environmental Qual Form All
Section 2 ends following the above documents
ENG-FORM: 805-0115.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.

This page intentionally left blank

246-xxx 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.
Conditions Section Description of Conducted Tests
Power input 16.0 Categories B and Z
•Emergency operating voltage was tested
Voltage spike 17.0 Category A
Audio frequency conducted
susceptibility 18.0 Category A
Induced signal susceptibility 19.0 Category A
Radio frequency susceptibility 20.0
Change No. 3 Category T
Emission of radio frequency
energy 21.0 Category Z.
Lightning induced transient
susceptibility 22.0 Change No. 2 Category XXC2
Lightning direct effect 23.0 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

Model 246 Isolation Amplifier
SM246 Installation and Operation Manual
Section 3 Rev: 1.00 Issue 2 Page 3-1
ENG-FORM: 806-0111.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
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