RF & Coaxial Cable Glossary
Plain-language definitions of terms used in RF engineering, coaxial cable specifications, and connector selection. Click any letter to jump to that section.
A
Attenuation
The reduction in signal strength as it travels through a coaxial cable, expressed in decibels (dB) per 100 feet. Attenuation increases with frequency and run length. Also called insertion loss or cable loss. A 3 dB loss means half your power is dissipated in the cable as heat.
Armored Cable
Coaxial cable with a metallic armor layer (typically corrugated copper or aluminum) over the outer jacket. Provides mechanical protection and rodent resistance for direct-burial or conduit installations.
B
Bandwidth
The range of frequencies over which a cable or connector performs within a specified attenuation or return loss spec. A cable rated DC–6 GHz maintains its specified electrical properties across that entire range.
Bend Radius (Minimum)
The tightest loop a coaxial cable can form without permanently damaging the dielectric or shifting the center conductor. Exceeding the minimum bend radius causes a permanent impedance discontinuity at the kink. RG-58: ~1.5 in. LMR-240: ~2 in. LMR-400: ~4 in. LMR-600: ~6 in.
BNC Connector
Bayonet Neill-Concelman connector. A quarter-turn bayonet-locking RF connector rated DC–4 GHz, used on oscilloscopes, spectrum analyzers, signal generators, CCTV cameras, and portable radios. Available in 50-ohm and 75-ohm versions that are physically identical but electrically incompatible.
Braid Shield
Woven wire mesh surrounding the dielectric of a coaxial cable, forming the outer conductor. Provides shielding against electromagnetic interference (EMI) and RF leakage. Coverage is expressed as a percentage — 95% braid coverage is typical for quality cables. Double-braid cables add a second braid layer for better shielding.
C
Capacitance (Distributed)
The capacitance per unit length between the center conductor and shield of a coaxial cable, expressed in pF/ft. Typical values range from 20–30 pF/ft. Higher capacitance limits bandwidth and affects impedance matching with some source and load types.
Characteristic Impedance
The impedance of a transmission line when terminated in a matched load, determined by the ratio of the center conductor diameter to the inner diameter of the shield and the dielectric constant. The standard for RF systems is 50 ohms. Cable TV and video systems use 75 ohms. Mixing impedances causes signal reflection and elevated SWR.
Coaxial Cable (Coax)
A transmission line consisting of a center conductor, dielectric insulator, outer conductor (shield), and protective jacket, all sharing the same axis. The coaxial geometry confines the RF signal between the center conductor and shield, preventing radiation and interference pickup.
Common-Mode Current
Unwanted RF current flowing along the outside surface of a coaxial cable shield, rather than between the center conductor and inner surface of the shield. Common-mode currents cause the cable to act as an antenna, both radiating interference and picking up noise. Suppressed with ferrite chokes.
Connector Gender
Male connectors have a protruding center pin; female connectors have a center socket. On standard SMA, the male has the pin. On RP-SMA (reverse polarity SMA), the male has a socket and the female has a pin — the opposite of standard. Always verify gender before ordering.
D
dB (Decibel)
A logarithmic unit expressing the ratio of two power levels. In RF, 3 dB = half the power; 6 dB = quarter power; 10 dB = one-tenth power. On the receive side, 3 dB of cable loss effectively doubles the noise figure of the following amplifier or receiver. Cable attenuation specs are given in dB per 100 feet.
Dielectric
The insulating material between the center conductor and outer shield of a coaxial cable. The dielectric material determines the cable's velocity factor, capacitance, and temperature range. Common materials: solid PTFE (Teflon) for maximum stability and temperature range; foam polyethylene for lower loss; solid polyethylene for economy cables.
Dielectric Loss
Signal power absorbed by the dielectric insulator as the electromagnetic field moves through it. Dielectric loss increases with frequency, making it a dominant loss mechanism at microwave frequencies. PTFE has very low dielectric loss, which is why it's used in high-frequency and precision cables.
Double-Shielded
A coaxial cable construction with two separate shielding layers — typically a foil (100% coverage) plus braid — providing greater than 90 dB of shielding effectiveness. Used in test bench applications, sensitive receive systems, and environments with strong interference sources.
E
Electrical Length
The phase delay introduced by a cable, expressed as a fraction of a wavelength or in degrees at a given frequency. Physical length × velocity factor = electrical length (in free-space wavelengths). Used in antenna phasing, cavity tuning, and delay line applications.
EMI (Electromagnetic Interference)
Unwanted electromagnetic energy that disrupts the operation of electronic equipment. Coaxial cables suppress EMI via their shielded construction. Higher shield coverage (double braid, foil+braid) provides better EMI rejection.
F
Fakra Connector
Color-coded automotive RF connector standardized by the German automotive industry (DIN 72594-1). Color indicates application: Z (black) = GPS/GNSS, A (beige) = SDARS/satellite, B (blue) = diversity TV, C (cream) = GSM. Used on OEM antenna ports in European and Asian vehicles.
FEP Jacket
Fluorinated Ethylene Propylene — a fluoropolymer jacket material used on high-temperature cables. Similar to PTFE but slightly more flexible, rated to +200°C. Used on RG-178 and other demanding-environment cables.
Foil Shield
A thin metallic foil (usually aluminum or copper) wrapped around the cable dielectric to form the outer conductor. Provides 100% coverage but cannot be soldered. Foil shields are almost always combined with a drain wire or braid to provide a solderable electrical contact point.
I
Impedance
Opposition to AC current flow in an RF circuit, expressed in ohms. For coaxial cable, this is the characteristic impedance — 50 ohms for RF/communications systems, 75 ohms for cable TV and video. Mismatching impedances causes signal reflection (SWR > 1.0). All cables, connectors, and equipment in an RF system should share the same impedance.
Impedance Matching
Ensuring that the source, transmission line, and load all present the same impedance to minimize reflections and maximize power transfer. At RF, impedance mismatch is measured by SWR — a perfect match is SWR 1.0:1. A tuner or matching network is used to transform one impedance to another.
Insertion Loss
The total signal reduction caused by inserting a cable, connector, or component into a circuit, expressed in dB. For a cable assembly, insertion loss includes both conductor loss and dielectric loss. Distinguished from return loss, which measures reflected energy rather than absorbed energy.
J
Jacket
The outer protective covering of a coaxial cable. Common materials: PE (polyethylene) for outdoor UV resistance; PVC for indoor general-purpose use; PTFE for high-temperature environments; TPE/TPU for highly flexible cables. The jacket color is often gray, black, or white — color has no electrical significance.
M
MCX Connector
Micro Coaxial connector — a snap-on connector about 30% smaller than SMB, used on GPS receivers, automotive head units, and compact RF modules. Rated to 6 GHz. Typically used with short RG-316 pigtails to bring the signal out to a larger connector.
MMCX Connector
Micro Miniature Coaxial — a snap-lock connector (rotating barrel) rated DC–6 GHz. Slightly larger than U.FL; found on industrial modules, WiFi cards, and some GPS receivers. Designed for about 500 mate/unmate cycles before degradation.
MIL-SPEC (Military Specification)
Cables and connectors manufactured to US military specifications (e.g., MIL-C-17 for coaxial cable). MIL-spec cables are tested to more stringent electrical, mechanical, and environmental standards than commercial-grade alternatives. RG-142 and RG-400 are common MIL-spec cables.
N
N-Type Connector
A precision threaded RF connector rated DC–11 GHz, IP67 weatherproof when mated. Named after Paul Neill of Bell Labs. The standard for outdoor antennas, commercial access points, repeaters, and cellular signal boosters. Handles 500+ watts at 1 GHz. The 7/16-inch hex coupling nut provides a reliable weatherproof seal.
Noise Figure
A measure of how much a device (amplifier, cable, receiver) degrades signal-to-noise ratio, expressed in dB. Every dB of cable loss directly adds 1 dB to the effective noise figure of the system. On receive paths (SDR, scanner, ADS-B), minimizing cable loss directly improves sensitivity.
P
Phase Stability
A cable's ability to maintain constant electrical length as it is flexed or subjected to temperature changes. Critical for test bench applications, VNA calibrations, and phased array systems. PTFE-dielectric cables have superior phase stability compared to foam-polyethylene cables.
Pigtail
A short cable assembly — typically 3–24 inches — used to connect a device's RF port to a larger connector or cable. Common examples: U.FL-to-SMA pigtail for a PCB module, or MMCX-to-SMA pigtail for a compact radio. Almost always uses thin flexible cable (RG-316, RG-174, or RGU-178).
PL-259 Connector
Also called UHF connector or SO-239 (female version). The standard antenna connector on ham radio HF transceivers. Despite the "UHF" name, its geometry is uncontrolled above ~300 MHz and it should not be used for serious VHF/UHF antenna connections. Not weatherproof — requires tape or boots for outdoor use.
PTFE (Polytetrafluoroethylene)
Trade name: Teflon. A fluoropolymer dielectric and jacket material used in high-performance RF cables (RG-142, RG-316, RG-400, RG-178). PTFE has very low dielectric loss (tan δ ≈ 0.0002 at 1 GHz), excellent phase stability, and a temperature rating to +260°C. Its low friction also makes cables easier to pull through conduit.
R
Return Loss
The ratio of incident power to reflected power at a connector or cable interface, expressed in dB. Higher return loss is better — 20 dB means only 1% of power is reflected. Return loss is the reciprocal of SWR expressed in dB. A well-matched connection at 2.4 GHz should show >20 dB return loss.
RP-SMA (Reverse Polarity SMA)
Physically identical to SMA but with reversed center pin polarity: RP-SMA male has a socket, RP-SMA female has a pin. Used on consumer WiFi routers, USB adapters, and access points to prevent unauthorized antenna connections. Incompatible with standard SMA — they will thread together but not make electrical contact.
S
Shield Coverage
The percentage of the cable surface covered by the outer conductor braid. 95–98% is typical for quality cables. Higher coverage provides better shielding and lower transfer impedance. Double-shielded cables (foil + braid) achieve near-100% coverage and typically >90 dB shielding effectiveness.
Skin Effect
At RF frequencies, current flows only on the outer skin of a conductor, not through its entire cross-section. The skin depth decreases with increasing frequency. This is why conductor resistance — and thus cable attenuation — increases with frequency. Silver-plating the copper conductor reduces skin-effect resistance at RF frequencies.
SMA Connector
SubMiniature version A. A precision threaded connector rated DC–18 GHz, used on SDR dongles, GPS modules, cellular modems, lab instruments, and professional RF equipment. Maximum torque is 8–12 in-lbs — over-tightening permanently damages the PTFE dielectric. Do not confuse with RP-SMA (WiFi equipment uses RP-SMA).
SMB Connector
SubMiniature version B. A push-on snap connector rated DC–4 GHz, used on precision timing equipment, GPS receivers, and telecom instruments. Smaller than BNC, faster to connect, but not as mechanically secure in vibration environments.
SWR (Standing Wave Ratio)
A measure of impedance mismatch in an RF system, expressed as a ratio (e.g., 1.5:1). SWR 1:1 is a perfect match with no reflected power. SWR 1.5:1 reflects about 4% of power. SWR 2:1 reflects about 11%. High SWR causes power loss and can overheat transmission line components. Most modern transceivers fold back power above SWR 2:1 to protect their final amplifier stage.
T
TNC Connector
Threaded Neill-Concelman — a threaded version of the BNC, rated DC–11 GHz. More resistant to vibration and better weatherproofing than BNC. Common on military radios, aviation equipment, and outdoor installations where vibration would cause BNC bayonet connections to loosen.
Transfer Impedance
A measure of a cable's shielding effectiveness — the voltage induced on the outside of the shield per unit current flowing inside (mΩ/m). Lower is better. Solid-outer-conductor cables (hardline) have near-zero transfer impedance. Braid cables: 1–10 mΩ/m. Poorly shielded cables: >100 mΩ/m.
U
U.FL / IPEX / IPX Connector
Ultra-miniature snap-on PCB connector (Hirose U.FL / Amphenol IPEX) rated DC–6 GHz. The connector body is approximately 2mm in diameter. Used on WiFi cards, LTE mini-PCIe modules, GPS chips, and IoT SoCs. Not intended for repeated connections — typically used with a permanent short pigtail to bring the signal out to a larger connector.
V
Velocity Factor (VF)
The speed of signal propagation through a cable as a fraction of the speed of light in free space. Determined by the dielectric material. PTFE cables: VF ≈ 0.69–0.70. Foam polyethylene (LMR-400): VF ≈ 0.85. Air dielectric hardline: VF ≈ 0.92–0.98. VF affects the electrical length of a cable for antenna matching and timing applications.
VSWR
Voltage Standing Wave Ratio — equivalent to SWR. The ratio of maximum to minimum voltage amplitude along a transmission line. VSWR = (1 + |Γ|) / (1 − |Γ|), where Γ is the reflection coefficient. Often used interchangeably with SWR in practice.
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