How to Select the Correct Replacement Aircraft Antenna

Start with the existing installation

Before comparing products, assemble a short identification record:

• Existing antenna manufacturer and complete part number, including suffixes.
• Aircraft make, model, serial number, and antenna location.
• Exact model of the connected radio, navigator, transponder, ELT, or other equipment.
• Relevant maintenance entries, equipment list, installation drawings, and modification records.
• Applicable antenna and equipment installation or maintenance instructions.
• Photographs of the antenna identification, mounting area, and accessible cable connection.

Use the aircraft records to establish what configuration was installed, then compare that information with the actual hardware. If the label and records disagree, resolve the discrepancy before ordering.

Suffixes deserve attention. RAMI’s AV-534 and AV-534L instructions, for example, describe different supplied cable arrangements despite their shared antenna family. A family name alone may not identify everything needed for the replacement. RAMI installation instructions

If the original part is unavailable, ask for documented supersession or replacement information. Record who identifies the substitute and the conditions attached to that identification. FAA replacement-parts guidance emphasizes eligibility, identification, and traceability; a catalog cross-reference should support that investigation, not end it. FAA AC 20-62E, Change 1

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Match the replacement aircraft antenna to the equipment

Identify the function before selecting the frequency range. “VHF antenna,” “GPS antenna,” and “transponder blade” are useful search terms, but incomplete specifications.

Apparently similar antennas can cover different bands. RAMI lists its AV-534 communications antenna for 118–137 MHz, while its AV-535 is listed for 138–174 MHz. Both appear in the manufacturer’s communications category; they do not cover the same operating range. RAMI COM antenna catalog

For the application being replaced, check the following distinctions:

• VHF COM: Confirm the radio’s complete required band, polarization, impedance, and transmitting-power requirements.
• NAV/VOR/LOC/glideslope: Identify the complete receiving arrangement, including any coupler or splitter. RAMI’s AV-585, for example, is a receive-only antenna coupler; replacing an external antenna does not eliminate the need to verify the associated components. RAMI AV-585 instructions
• Transponder, Mode S, ADS-B, and DME: Determine the exact equipment and RF connection involved. ADS-B Out may use a 1090 MHz extended- squitter transponder or a 978 MHz UAT. “ADS-B compatible” without the system and frequency is insufficient purchasing information. An antenna sold for transponder/DME use still requires equipment-specific verification. FAA ADS-B installation guidance, FAA ADS-B frequencies
• Marker beacon: Confirm the dedicated receiver installation. A low-profile receiving antenna should not be identified by shape alone; RAMI explicitly identifies its marker-beacon models as receive-only. RAMI marker-beacon catalog
• Multifunction antennas: Verify every function and port. RAMI’s AV-290, for example, assigns different frequency bands to its BNC and TNC connections. One compatible connection does not establish compatibility for the entire assembly. RAMI AV-290 specifications

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Give GPS/GNSS and ELT replacements extra scrutiny

For an active GPS/GNSS antenna, check the receiver’s permitted antenna models or performance requirements, including amplifier power, gain, and cable-loss requirements. The Trig TN72 illustrates why frequency alone is insufficient: its receiver powers the antenna’s low-noise amplifier through the coax. Trig TN72 installation manual

For an ELT, verify the antenna against the exact ELT system documentation. ARTEX’s ELT 345 manual, Revision P, requires an antenna approved for use with that unit and separately requires suitability for the aircraft installation. A matching connector and advertised frequency coverage are not sufficient evidence. Confirm the applicable current manual before selecting the replacement. ARTEX ELT 345 manual, Rev. P

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Compare electrical specifications as a set

Check nominal impedance, VSWR over the required band, polarization, radiation-pattern requirements, and RF power handling together.

Where the equipment specifies a 50-ohm antenna system, the replacement antenna and transmission line must satisfy that requirement. Do not assume that every aviation antenna or every coaxial connector is interchangeable merely because 50-ohm systems are common.

Read VSWR specifications with their frequency ranges and stated conditions. A favorable value at one frequency does not establish acceptable performance across the required band. RAMI’s AV-289 data sheet, for example, gives different VSWR limits for different portions of its coverage.

For transmitting systems, compare the equipment’s requirements with the antenna’s applicable power rating. Peak and continuous ratings are distinct specifications; the AV-289 sheet lists them separately. A receive-only product should not be selected for a transmitter without explicit supporting documentation. RAMI AV-289 data sheet

Treat catalog specifications as the starting point for comparison. The installed system must also meet the applicable inspection and operational-test requirements.

Verify the connector and cable termination

Aircraft antenna products use connector families including BNC, TNC, N-type, and SMA. Dayton-Granger’s antenna catalog includes all four, but the exact antenna variant determines the connection. Dayton-Granger antenna catalog

Record more than the connector family:

• Plug or receptacle, including the specified contact arrangement.
• Required impedance and frequency capability.
• Straight or angled connection and available mating clearance.
• Compatibility of the cable connector with the actual coax.
• Required assembly, securing, and environmental protection.

Appearance is insufficient. Amphenol, for example, offers BNC adapters for both 50-ohm and 75-ohm applications. A familiar connector outline does not establish the correct electrical specification. Amphenol BNC adapters

An adapter is not automatically an acceptable substitute for the specified connection. Check whether the installation data permits the arrangement, whether it fits, and whether its loss is included in the system calculation. Garmin explicitly accounts for connector and adapter losses in its GPS antenna installation guidance. Garmin 400W Series installation manual

Compare the mounting drawing with the aircraft

Electrical compatibility does not establish mechanical interchangeability. Compare the manufacturer’s installation drawing with the existing mounting provisions before committing to a replacement.

Ask the installer to check the space beneath the skin, not just the visible footprint. Include room for the mating connector, cable bend, hardware, and access.

Mounting-surface curvature also matters. FAA AC 43.13-2C favors a flat mounting surface and warns against overtightening fasteners to distort the aircraft structure into contact with the antenna base. Its structural-support guidance also addresses loading, vibration, and flutter. FAA AC 43.13-2C, Chapter 4, § 4.4

Dayton-Granger’s installation guidance specifically addresses mounting holes, doublers, hardware, gaskets, and sealing. Determine which items the replacement includes and which must be ordered separately. Dayton-Granger installation guidance

Check the ground plane and electrical bond separately

For antenna designs that require a ground plane, the conductive surface forms part of the RF installation. Trig’s transponder instructions explain that a conventional monopole relies on this surface for correct operation. Metal skin can provide it; composite or fabric construction may require an added conductive plane. Trig TT21/TT22 installation manual

Requirements vary by antenna design and equipment installation. Do not adopt a generic aircraft antenna ground-plane size.

For example, Trig’s TA14 guide addresses installation on metal-skinned aircraft and requires an added metallic ground plane behind the antenna on composite aircraft. It specifies at least 150 cm², with 24 square inches given parenthetically. Those are the manufacturer’s printed values, not an exact unit conversion. Confirm the required dimensions against the applicable instructions before fabrication. These are TA14 instructions, not a universal requirement for COM, GPS, ELT, or other antennas. Trig TA14 installation guide

Electrical bonding is a related but separate check. Where the design requires a conductive connection to the airframe or ground plane, the installation must provide that connection through the prescribed path.

Dayton-Granger’s guidance includes surface preparation, sealing, and a measured bond check, linking the bond to lightning protection and radiation-pattern performance. Use the requirements applicable to the actual antenna and aircraft; do not transfer a resistance limit or surface-preparation procedure from an unrelated installation. Dayton-Granger installation guidance

Before ordering, establish whether the existing ground plane and bonding arrangement can be retained.

Evaluate the coax, not just the antenna

A replacement decision should include the existing cable assembly. Have the installer assess cable condition, termination quality, routing, moisture protection, and compliance with the equipment’s loss requirements.

Coax attenuation depends on cable type, length, and operating frequency. Manufacturer cable data shows that attenuation rises with frequency, so a run acceptable for a lower-frequency application may have excessive loss in a higher-frequency system. Use attenuation data at the relevant frequency, not a convenient value elsewhere on the data sheet. Harbour M17/128-RG400 cable data

Account for the complete RF path, including connectors and any permitted intervening components.

Garmin’s GTX 23 installation manual, Revision J, provides a useful example: it limits attenuation between the unit and antenna to 1.5 dB at 1090 MHz, including connectors. Its cable-selection table relates permissible run length to cable attenuation. That is a GTX 23 requirement, not a general transponder limit. Garmin GTX 23 installation manual

Do not assume that the shortest possible cable always satisfies the equipment. Garmin’s older 400W Series manual, Revision G, specifies both minimum and maximum GPS antenna cable loss, with different limits for different antenna groups. This illustrates why the current instructions for the actual equipment-and-antenna combination must control cable selection. Garmin 400W Series installation manual

If the proposed antenna needs a different connector, include the cost and feasibility of a compliant cable assembly in the purchasing decision.

Confirm that the location remains suitable

A replacement should preserve the required coverage and separation for the installed system.

For GPS, Trig’s TN72 instructions call for an unobstructed view of the sky and separation from transmitting antennas that could cause interference. For the GTX 23 transponder installation, Garmin specifies a bottom-mounted antenna and addresses shadowing by nearby structures and openings. These are application-specific instructions. Trig TN72 manual, Garmin GTX 23 manual

Check nearby antennas, metal protrusions, landing gear, doors, and other structures. A changed antenna height or form factor deserves review even when the mounting position remains unchanged.

FAA AC 43.13-2C explains that separation depends on operating frequency and system characteristics, and that gear or flap extension can affect belly-mounted antenna performance. Use applicable equipment and antenna instructions to establish spacing; general guidance is not a universal separation rule. FAA AC 43.13-2C, Chapter 4, §§ 4.2.2 and 4.7

Plan the required interference and operational checks before ordering, particularly when substituting a different model.

Check airspeed and environmental limitations

Compare the antenna’s maximum rated airspeed, altitude limitations, and environmental qualification with the installation requirements. Confirm the exact variant and the basis of any speed rating rather than treating a catalog number as self-explanatory.

Review relevant vibration, temperature, moisture, and external-exposure qualifications. A blade or whip description alone establishes none of these limits. RAMI, for example, publishes model-specific operating limits for its AV-534 and separate environmental information for its airborne RAV30512. Those qualifications belong to those products. RAMI AV-534, RAMI RAV30512

For ELT antennas, ARTEX also directs the installer to consider aircraft speed, location restrictions, and aerodynamic loading. An electrically suitable antenna may still be unsuitable for the intended airframe installation. ARTEX ELT 345 manual, Rev. P

Establish the installation basis before purchase

Keep these distinctions clear:

• TSO authorization: FAA design and production approval showing that an article meets the applicable minimum performance standard. It does not, by itself, approve installation on a particular aircraft.
• Application suitability or eligibility: Evidence that the exact part meets the requirements and limitations of the intended equipment and application.
• Aircraft installation approval: The applicable basis for installing that article in the particular aircraft configuration.

The FAA expressly distinguishes TSO authorization from installation approval. An eligible article still needs an appropriate installation basis. FAA TSO guidance

Likewise, distinguish purchasing descriptions:

• Manufacturer-declared direct replacement: An explicit replacement statement whose scope and conditions must be checked.
• Equivalent specifications: Matching published characteristics that support comparison but may not address every installation requirement.
• Physically similar product: A resemblance that establishes no substitution approval.
• Approved substitute for the installation: A replacement supported by the applicable aircraft or alteration data and approval basis.

Have the installer identify that basis before ordering a substitute. For work subject to Part 43, the performance rules require current manufacturer maintenance instructions or other methods acceptable to the Administrator, subject to the regulation’s provisions. 14 CFR § 43.13

FAA AC 43.13-2C superseded AC 43.13-2B on July 29, 2026. The current AC addresses inspection and alteration of nonpressurized areas of civil aircraft weighing 12,500 pounds gross weight or less. Its data generally concerns minor alterations. Use as approved data for a major alteration is conditional: the data must be appropriate, directly applicable, and consistent with manufacturer data, with the specified chapter, page, and paragraph identified in the required Form 337 entry. Antenna installation is now Chapter 4. The AC is not blanket approval for an antenna substitution. FAA AC 43.13-2C status and scope

Experimental aircraft require assessment under their applicable certification and operating limitations. Do not assume that every certificated-aircraft maintenance provision applies identically; Part 43 contains specific applicability exceptions. 14 CFR § 43.1

Before ordering: practical replacement antenna checklist

Confirm and record:

• 01Existing antenna manufacturer and complete part number.
• 02Aircraft model, serial number, airframe material, and mounting location.
• 03Exact connected equipment and every function served.
• 04Required frequency coverage, impedance, polarization, and VSWR.
• 05Applicable transmit-power rating or receive-only designation.
• 06Active-antenna power and performance requirements, where applicable.
• 07Connector family, mating configuration, cable compatibility, and clearance.
• 08Mounting-hole pattern, base dimensions, height, and internal space.
• 09Surface contour, support or doubler requirements, and specified hardware.
• 10Ground-plane arrangement and electrical-bonding requirements.
• 11Gasket, sealing materials, and installation-kit contents.
• 12Coax condition, type, length, shielding, and complete allowable loss.
• 13Location, separation, shadowing, and interference requirements.
• 14Airspeed, altitude, and environmental limitations.
• 15Applicable aircraft and equipment documentation, including revision status.
• 16Documentary basis for any supersession, direct-replacement claim, or approved substitution.
• 17Part identification, traceability documents, and required installation checks.

Ask the installer to resolve any unanswered item that could change the part selection before placing the order.