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TEC-ELEC48-06 · Lesson 5 · 14.5 clock hours · lab

Coaxial Connectors and Termination Lab

Objective. Students terminate coaxial cables with N-type, PL-259 (UHF), F-type, and BNC connectors using the correct tools and technique, achieving measured insertion loss within the connector manufacturer's specified maximum.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by an industry-certified professional or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

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Coaxial Connectors and Termination

A coaxial assembly is only as good as its connectors. A poorly terminated connector introduces excess insertion loss, reflects signal power back toward the source, and can fail mechanically in the field. This lab covers the four connector types you will encounter most often in electronics and telecom work: the N-type, PL-259 (UHF), F-type, and BNC.

Why Termination Quality Matters

Coaxial cable carries RF signal on the center conductor and returns it through the outer braid or foil shield. The connector must maintain the same characteristic impedance as the cable — typically 50 Ω or 75 Ω — across the transition from cable to device. Any gap, misalignment, or solder bridge at that transition creates an impedance discontinuity. The result is reflected energy (measured as return loss) and energy absorbed by the connector itself (measured as insertion loss). Manufacturers publish a maximum insertion loss for each connector, and professional installations must meet that figure.

Connector Types at a Glance

N-type connectors are threaded, weatherproof, and rated for use well into the microwave range. They are common on test equipment, base-station antennas, and outdoor RF runs. N-type connectors are available in 50 Ω and 75 Ω versions; the two are not interchangeable — using the wrong impedance version degrades performance. Most field installations use the crimp style on LMR-240 or similar cable.

PL-259 (UHF) connectors are the large, threaded connectors found on amateur radio equipment, marine VHF radios, and some two-way radio installations. Despite the name "UHF," the design does not maintain controlled impedance and is best suited to frequencies below about 300 MHz. The PL-259 uses a solder-and-screw assembly; the mating socket is the SO-239.

F-type connectors are the standard for cable television, satellite, and over-the-air broadcast distribution. They are inexpensive, small, and available in crimp and compression (push-on) styles. The center conductor of the coaxial cable itself — typically RG-6 — serves as the contact pin, so proper strip length is critical. F-type is a 75 Ω system.

BNC connectors use a quarter-turn bayonet locking mechanism. They are rated to at least 4 GHz on precision versions and are the connector of choice for test-bench work, video (75 Ω), and many 50 Ω instrument connections. Crimp BNC connectors are the most common field type.

Strip Dimensions and Manufacturer Instructions

Every connector manufacturer publishes a specification sheet that lists exact strip dimensions: how much outer jacket to remove, how much braid to fold back or trim, and how much dielectric to remove to expose the center conductor. Always use the manufacturer instruction sheet for the specific connector and cable combination you are working with. Strip dimensions vary by connector family, cable diameter, and whether the connector is crimp or solder type. Using the wrong dimension is the single most common cause of failed assemblies.

Use a dedicated cable-prep tool for each cable size. These tools are set to the correct strip depths and produce clean, square cuts that hand-stripping with a knife cannot reliably match.

Termination Sequence Overview

The general sequence for a crimp connector is: (1) slide any required ferrule or crimp ring onto the cable first — this step cannot be undone after the connector body is on; (2) strip the cable to manufacturer dimensions; (3) fold or trim the braid as specified; (4) seat the center conductor fully into the contact; (5) verify the connector body is fully seated before crimping; (6) apply the correct crimp die and compress fully in one stroke. For solder connectors such as the PL-259, the sequence adds a tinning step on the braid, soldering through the solder holes in the barrel, and soldering the center pin — always allowing each joint to cool before handling.

Torque the mating threads to the manufacturer's specified value using a calibrated torque wrench. Hand-tight is not sufficient for RF connectors in service; over-torquing can crack the dielectric.

Safety in This Lab

Soldering station: Keep the iron in its holder when not in use. Solder containing lead requires hand washing after handling; use lead-free solder where required by your instructor. Work in a ventilated area to avoid inhaling flux fumes. Wear safety glasses.

Crimping tools: Keep fingers clear of the crimp die. Inspect tools for cracks before use.

VNA / test equipment: Follow the instrument's power-on and port-connection procedures. Do not exceed the VNA port's maximum input power. Zero (calibrate) the instrument before measuring; an uncalibrated VNA reading is meaningless.

General: Coaxial cable cut ends are sharp. Dispose of cable trim and braid scraps in the designated container to prevent puncture injuries.

Continuity Check Before RF Testing

Before connecting any assembly to the VNA, perform a continuity check with the coaxial continuity tester: verify the center conductor reads continuous end-to-end and that there is no short between center conductor and shield. A shorted assembly connected to a VNA port can damage the instrument.

Interpreting Insertion Loss Results

Insertion loss is expressed in decibels (dB) as a positive number representing signal lost through the device. A manufacturer might specify a maximum insertion loss of 0.2 dB for an N-type connector at 1 GHz. If your VNA measurement reads 0.15 dB, the assembly passes. If it reads 0.35 dB, the assembly fails and must be remade. Record the measured value, the manufacturer maximum, and a pass/fail notation in your lab log for each of the six assemblies.

Key terms8

Insertion lossThe signal power lost as a result of inserting a component (such as a connector) into a transmission line, expressed in decibels (dB). Lower is better.
Return lossA measure of how much signal power is reflected back toward the source at a discontinuity, expressed in dB. Higher return loss means less reflection and a better impedance match.
Characteristic impedanceThe constant impedance (typically 50 Ω or 75 Ω) that a coaxial cable and its connectors must maintain to prevent signal reflections.
Crimp connectorA coaxial connector that is mechanically secured to the cable by deforming a metal ferrule with a dedicated crimp tool, creating a permanent, gas-tight connection.
Strip dimensionsThe exact lengths of outer jacket, braid, and dielectric that must be removed to prepare a cable end for a specific connector, as listed in the manufacturer's instruction sheet.
Vector network analyzer (VNA)A test instrument that measures both magnitude and phase of RF signals transmitted through or reflected by a device under test, used to quantify insertion loss and return loss.
Impedance discontinuityA point in a transmission line where the impedance changes abruptly, causing some signal energy to be reflected rather than transmitted.
Compression connectorAn F-type or similar coaxial connector that is installed by pushing an internal sleeve onto the cable end with a compression tool, sealing the connector body around the cable jacket.

Worked examples4

1. Your VNA measures an insertion loss of 0.18 dB for a completed BNC assembly. The manufacturer's maximum specified insertion loss is 0.20 dB. Does the assembly pass or fail?
  1. Identify the measured value: 0.18 dB insertion loss.
  2. Identify the manufacturer maximum: 0.20 dB insertion loss.
  3. Compare: 0.18 dB ≤ 0.20 dB.
Answer: The assembly passes because the measured insertion loss is at or below the manufacturer maximum.
2. You measure insertion loss in dB and need to express that loss as a percentage of input power. If an N-type connector shows 0.10 dB insertion loss, what percentage of power is lost?
  1. Use the power ratio formula: Power ratio = 10^(−dB/10).
  2. Calculate: 10^(−0.10/10) = 10^(−0.01) ≈ 0.9772.
  3. This ratio represents the power transmitted (97.72% of input power passes through).
  4. Power lost = 100% − 97.72% = 2.28%.
Answer: Approximately 2.3% of input power is lost in the connector, confirming that even a small dB loss represents a measurable reduction in signal power.
3. An F-type connector instruction sheet specifies the following strip dimensions for RG-6: remove 12 mm of outer jacket, fold back and trim the braid flush with the jacket edge, remove 6 mm of dielectric (exposing the center conductor). Your cable prep tool is set for 10 mm jacket removal. How far off is the center conductor exposure if you use the wrong setting?
  1. The instruction sheet requires 12 mm jacket removal and 6 mm dielectric removal, leaving 12 − 6 = 6 mm of braid exposed at the correct setting.
  2. With the tool set at 10 mm jacket removal (and assuming the dielectric cut remains at 6 mm from the new jacket edge), the exposed center conductor length stays at 6 mm but the braid/jacket region is 2 mm shorter than specified.
  3. The connector body is designed for the 12 mm dimension; seating the connector with only 10 mm of prepared jacket may prevent the center conductor from fully engaging the contact pin by approximately 2 mm.
  4. A center pin that is 2 mm short of full engagement can cause intermittent contact and high insertion loss.
Answer: The center conductor would be approximately 2 mm short of full engagement in the contact, likely causing a high-insertion-loss or failed assembly. Always set the prep tool to the exact manufacturer strip dimension.
4. Two coaxial assemblies are tested. Assembly A measures 0.15 dB insertion loss; Assembly B measures 0.30 dB. The spec maximum is 0.20 dB. By how many dB does Assembly B exceed the limit?
  1. Identify the excess: 0.30 dB − 0.20 dB = 0.10 dB over the maximum.
  2. Assembly A: 0.15 dB ≤ 0.20 dB — passes.
  3. Assembly B: 0.30 dB > 0.20 dB — fails by 0.10 dB.
Answer: Assembly B exceeds the manufacturer maximum by 0.10 dB and must be remade.

The math in this lesson2

Learners compare measured 0.18 dB insertion loss to a 0.20 dB manufacturer maximum.
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Brush up in the math halls at newSchoolWorks.com:
In class: Watch instructor demonstrate the full crimp/solder termination sequence for each connector type on the appropriate cable, noting strip dimensions from the manufacturer instruction sheet, then repeat the demonstration on practice cable ends. · Terminate a set of six coaxial assemblies (one per connector/cable pairing assigned by instructor) following printed step-by-step instructions; use a coaxial continuity tester to verify center-conductor and shield integrity before submitting. · Measure insertion loss of each completed assembly at a designated test frequency using a vector network analyzer or scalar return-loss bridge; record results in a lab log and compare to manufacturer maximum insertion-loss specification.
Materials: Coaxial cable samples (RG-6, RG-58, LMR-240), N-type, PL-259, F-type, and BNC connector kits, cable-prep tools, crimping tools, torque wrench, soldering station, continuity tester, vector network analyzer or return-loss bridge, manufacturer instruction sheets
Check: All six assemblies pass continuity check and measure insertion loss at or below manufacturer maximum; any assembly exceeding spec must be redone before the lab is signed off.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

ETA CET — Safety and Test Equipment
1. Before connecting a completed coaxial assembly to a VNA port, the FIRST verification step should be:
ETA FOI/FOT — RF and Coaxial Systems
2. The characteristic impedance of the F-type connector system used in cable television distribution is:
ETA CET — RF Fundamentals
3. A technician installs a PL-259 connector on RG-58 cable for use at 600 MHz. Which statement BEST describes a limitation of this choice?
BICSI Installer — Installation Quality and Testing
4. A completed N-type connector assembly is measured on a VNA and shows 0.25 dB insertion loss. The manufacturer maximum is 0.20 dB. What action is required?
ETA CET — Connectors and Cabling
5. Which of the following connector types uses a quarter-turn bayonet locking mechanism?
ETA FOI/FOT — Fiber and RF Connector Installation
6. When terminating a crimp-style coaxial connector, which step MUST be completed before sliding the connector body onto the cable?
BICSI Installer — Standards and Manufacturer Requirements
7. Strip dimensions for coaxial connectors should be taken from:
ETA CET — RF Calculations and Measurements
8. Insertion loss is expressed in decibels. If an assembly has 0.10 dB insertion loss, the fraction of input power that is TRANSMITTED through the connector is closest to:
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