Garmin GTXTM 327 TRANSPONDER INSTALLATION MANUAL
Brand: Garmin, Pages: 55
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Page 8GTX 327 Installation Manual
2.3.3 Installation Approval Considerations for Pressurized Aircraft
Antenna and cable installations on pressurized cabin aircraft require FAA approved installation design
and engineering substantiation data whenever such installations incorporate alteration (penetration) of the
cabin pressure vessel by connector holes and/or mounting arrangements.
For needed engineering support pertaining to the design and approval of such pressurized aircraft antenna
installations, it is recommended that the installer proceed according to any of the following listed
1. Obtain approved antenna installation design data from the aircraft manufacturer.
2. Obtain an FAA approved Supplemental Type Certificate (STC) pertaining to and valid for the
subject antenna installation.
3. Contact the FAA Aircraft Certification Office in the appropriate Region and request identification
of FAA Designated Engineering Representatives (DERs) who are authorized to prepare and
approve the required antenna installation engineering data.
4. Obtain FAA Advisory Circular AC-183C and select (and contact) a DER from the roster of
individuals identified thereunder.
5. Contact an aviation industry organization such as the Aircraft Electronics Association and request
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GTX 327 Installation ManualPage 9
2.3.4 Antenna Cable Installation
When routing antenna cables, observe the following precautions:
•All cable routing should be kept as short as possible and as direct as possible.
•Avoid sharp bends.
•Avoid routing cables near power sources (e.g., 400 Hz generators, trim motors, etc.) or
near power for fluorescent lighting.
•Avoid routing cable near ADF antenna cable (allow at least a 12-inch separation).
The following table lists examples of the recommended antenna cable vendors and the type of cable to be
used for specific lengths of cable. Any cable meeting specifications is acceptable for the installation. The
maximum coaxial cable attenuation at 1090 MHz must not exceed 1.5 dB.
Table 2-1. Recommended Antenna Cable Type
Max. Length (feet) ECS Type MIL-C-17 Type RG Type
8.8 M17/128 RG400
12.5 M17/112 RG304
17.0 311601 M17/127 RG393
Supplier InformationVendor: Electronic
5300 W. Franklin Drive
Franklin, WI 53132
www.ecsdirect.comMIL-C-17 types: See
current issue of
Qualified Products List
QPL-17.RG types: See current
issue of Qualified
Products List QPL-17.
2.3.5 Antenna Cable Connectors
One of two rack connectors are provided (item 6 or 12 in the installation drawing, figure B2 on page 39).
RF Adapter item 12 (Garmin P/N 330-00326-00) requires the cable to be terminated to an appropriate
type BNC plug (provided by installer), which is then attached to item 12. Any 50 ohm, double shielded
cable may be used, provided it introduces less than 1.5 dB attenuation at 1 GHz including the connector.
Connector item 6 (Garmin P/N 330-00198-00) requires the cable to be terminated directly to it and can
accommodate only M17/128 (RG-400) cable. The completed cable including connectors must introduce
no more than 1.5 dB attenuation at 1 GHz. Instructions for installing the item 6 are shown below (steps
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Page 10 GTX 327 Installation Manual
Figure 2-1. RF Connector Assembly
A. Trim coax outer insulation back 0.50”.
B. Trim braid (not center conductor or insulation) back 0.25”.
C. Strip Insulation back 0.12”.
Place the ferrule over the coax braid, flush against the coax outer insulation before
performing the next step if the outside diameter of the coax braid is smaller than the inside
diameter of the center connector sidewall opening.
D. Insert cable (center conductor, dielectric and shield braid) through the sidewall of the
connector and solder the center conductor to the center pin of the connector.
When using low loss cable it may be necessary to flatten the solid wire center conductor
slightly so it can fit the slot on the RF connector center pin. When soldering, avoid applying
excess heat to the connector body, and center conductor insulator.
E. Heat the outside of the connector sleeve and at the same time apply solder between the braid
and the sleeve. Continue to apply heat until the solder flows evenly.
F. Install 50 1 Matching Bushing.
G. Insert connector cap and tack solder in two places.
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GTX 327 Installation Manual Page 11
2.4 GTX 327 INSTALLATION
Avoid installing the unit near heat sources. If this is not possible, ensure that additional
cooling is provided. Allow adequate space for installation of cables and connectors. The
installer will supply and fabricate all of the cables. All wiring must be in accordance with
FAA AC 43.13-1B and AC 43.13-2A.
A. Assemble the connector/rack kit according to figure B2. Install the rack assembly
according to the dimensions given in figure B1 and paragraph 1.4.2, Physical
Characteristics of the GTX 327. Mounting brackets are not supplied due to the wide
range of mounting configurations available. Suitable mounting brackets may be
fabricated from sheet metal or angle stock. To ensure a sturdy mount, provide rear
support for the unit.
B. The two recessed screw holes in the rear plate are not used. Do not insert screws through
the rear plate of the mounting rack into the transponder, as the two holes are not intended
for use with the GTX 327. Refer to figure B2.
C. Looking at the bottom of the transponder, make sure the front lobe of the locking
mechanism is in a vertical position. This can be accomplished by using a 3/32” Allen
wrench through the face plate.
D. Slide the unit into the rack until the front lobe of the unit touches the rack. Guide pins on
the back plate will help in the proper alignment of the unit in the rack.
E. Turn the Allen wrench clockwise until the unit is secured in the rack. Continue turning
until tight. Do not overtighten the screw.
F. To remove the unit from the rack, turn the 3/32” Allen wrench counterclockwise until it
disengages from the rack.
2.5 COOLING AIR
The GTX 327 meets all applicable TSO requirements without forced-air cooling. The application of
forced-air cooling to the rear heat sink of the GTX 327 provides beneficial cooling to the unit. The
GTX 327 is designed to dissipate its internal heat to the rear heat sink without the need of blowing air
inside the unit.
The GTX 327 was designed to handle a constant 450 PRF, with short periods of 1200 PRF. Rate limit is
set at 1200 PRF. A typical radar site would interrogate the transponder once every 5 to 10 seconds for
approximately 100 msec at a 400 PRF rate. In very high traffic areas with multiple ground stations and
TCAS traffic it is possible to have long term PRF rates above 450 PRF. The GTX 327 measures the unit
temperature and without forced-air cooling the reply rate will be reduced to protect the transmitter from
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Page 12 GTX 327 Installation Manual
2.6 ELECTRICAL CONNECTIONS
All electrical connections, except for the antenna, are made through a single, 25-pin D subminiature
connector. Table 2-4 defines the electrical characteristics of all input and output signals and identifies the
cable requirements for each signal. Required connector and associated hardware are supplied with the
Mounting Rack, Backplate and Connector kit (Garmin P/N 010-10161-01). See figures B4 and B5 on
pages 43 and 45 for interconnect wiring diagrams.
Larger pins are supplied for the connector to provide power and ground at pins 13, 14, 15, and 25 when
required. Refer to figure B4, Note 1.
Table 2-2. Pin Contact Part Numbers
25 pin connector (P3271)
Wire Gauge 18 AWG 20-24 AWG
Garmin P/N 336-00023-00 336-00022-00
Military P/N N/A M39029/63-368
AMP N/A 205090-1
Positronic FC6018D M39029/63-368
ITT Cannon See Note 3 031-1007-042
Table 2-3. Recommended Crimp Tools
Wire Gauge18 AWG 20-24 AWG
Extraction ToolPositioner Insertion/
Military P/N M22520/2-01 N/A M81969/1-02 M22520/2-08 M81969/1-02Positronic 9507 9502-11 M81969/1-02 9502-5 M81969/1-02ITT Cannon 995-0001-584 N/A N/A 995-0001-604 980-2000-426AMP 601966-1 N/A N/A 601966-5 91067-2Daniels AFM8 K774 M81969/1-02K13-1 M81969/1-02Astro 615717 N/A M81969/1-02 615724 M81969/1-02
1. Insertion/extraction tools from ITT Cannon are all plastic; others are plastic with metal tip.
2.Non-Garmin part numbers shown are not maintained by Garmin and consequently are subject
to change without notice.
3. Alternate contacts for 18 AWG wire: As an alternative to the Positronic contacts listed (and
provided in the installation kit), the installer may use contacts made by ITT Cannon under P/N
031-1007-001. These contacts require the use of a different crimp tool positioner than shown
in the table, with the part numbers as follows: Daniels P/N K250, Astro P/N 616245, or ITT
Cannon P/N 980-0005-722.
4. All wires must be passed through the backshell before being assembled to connector.
5. In aircraft equipped with a dropping resistor for +28 Vdc bus voltage, make sure the dropping
resistor is bypassed.