Why must RF cable cuts be perpendicular?

A non-square cut creates: (1) Uneven dielectric surface: the connector's center contact may not seat properly against the dielectric, creating an air gap. This gap changes the impedance at the connector transition and creates a reflection (VSWR degradation). (2) Connector seating issues: the cable outer conductor must mate flush with the connector body. An angled cut prevents full circumferential contact, degrading both the mechanical connection and the shield continuity. (3) Center conductor protrusion: if the cut angle causes the center conductor to extend beyond the dielectric on one side, it may protrude too far into the connector and damage the mating connector's center contact. (4) For semi-rigid cable: an angled cut on copper tube outer conductor creates burrs that prevent the connector from sliding on. The cut must be perfectly square and deburred.

What tools are used for RF cable cutting?

(1) Rotary cable cutter: the standard tool for flexible coax (RG-series, LMR). A rotating blade scores and cuts the cable cleanly without crushing. Knipex, Klein, and Greenlee make quality rotary cutters. (2) Die-based cutter (hardline): uses matched dies to cut corrugated and smooth-wall hardline cable. The die prevents deformation of the cable. Andrew/CommScope and RFS provide cable-specific cutters. (3) Abrasive wheel (corrugated hardline): a thin abrasive disc cuts through the corrugated outer conductor without deforming it. Used for large-diameter (1-5/8 inch and above) hardline. (4) Tube cutter (semi-rigid): score-and-snap cutters for semi-rigid cable (0.047, 0.085, 0.141 inch). The outer conductor is scored with a cutting wheel, then snapped cleanly. Must not deform the tube. (5) Scissors/diagonal cutters: NEVER use for coaxial cable. These crush the cable, deform the outer conductor, and create jagged cuts.

How do you determine cable cut length?

Cable length must account for: (1) End-to-end routing distance: measure the actual path including all bends and vertical runs. Add extra for service loops at each end (typically 0.3-1m per end). (2) Connector take-up: each connector takes up a portion of the cable. This varies by connector type: N-type crimp: ~15mm per end. 7/16 DIN clamp: ~25mm per end. (3) Electrical length: for phase-matched cables (antenna arrays, combining networks), the electrical length must be controlled. Physical length = electrical length × velocity factor. Temperature: electrical length changes with temperature (~2 ppm/°C for foam cables). (4) Tolerance: typical length tolerance for cell site jumpers: ±5mm. For phase-matched sets: ±1mm or better. (5) Best practice: always cut cables slightly longer than required. You can trim, but you cannot add length. Mark cable ends before cutting with a square and tape to guide the cut.

Cable Assembly

Cable Cutting

/kay-bul kut-ting/

Perpendicular cut to axis: rotary cutter (flex coax), die cutter (hardline), abrasive wheel (corrugated), tube cutter (semi-rigid). Never scissors/diagonal cutters (crush cable). Tolerance: ±5mm (cell jumpers), ±1mm (phase-matched). Deburr outer conductor. Account for connector take-up (15-25mm per end) and service loops.

Tolerance: ±1-5mm

Tool: Rotary cutter

Critical: Square cut

Understanding Cable Cutting

A clean cable cut is the foundation of every good cable assembly. The cut surface is where the cable meets the connector, and any imperfection here propagates through the entire assembly as degraded return loss, poor connector seating, or mechanical unreliability. The right cutting tool for each cable type ensures a square, clean, burr-free end that allows the connector to seat properly and the impedance transition to function as designed.

Cut Quality Impact

Cable Cutting:
Perpendicular cut to axis: rotary cutter (flex coax), die cutter (hardline), abrasive wheel (corrugated), tube cutter (semi-rigid). Never scissors/diagonal cutters (crush cable). Tolerance: ±5mm (cell...

Key specifications:
5 mm | 1 mm | -25 mm

Power: P(dBm) = 10log(P_mW), 0dBm = 1mW

Cutting Tool Comparison

Tool	Cable Type	Cut Quality	Speed	Example
Rotary cutter	Flexible coax	Excellent	Fast	Knipex, Klein
Die cutter	Hardline	Excellent	Medium	Andrew/CommScope
Abrasive wheel	Large corrugated	Good	Slow	1-5/8"+
Tube cutter	Semi-rigid	Excellent	Medium	Score and snap
Scissors/diag	NEVER for coax	Terrible	N/A	Crushes cable

Key Equations

Decibel conversion:
Power: dB = 10log(P₂/P₁)
Voltage: dB = 20log(V₂/V₁)

dBm to watts:
P(W) = 10^{(dBm−30)/10}
0 dBm = 1 mW, +30 dBm = 1 W

Wavelength:
λ = c/f = 300/f(MHz) meters

Comparison

Connector	Freq Max	Impedance	Power	Interface
SMA	18 GHz	50 Ω	0.5 W	Threaded
N-Type	11 GHz	50 Ω	5 W	Threaded
2.92mm (K)	40 GHz	50 Ω	0.3 W	Threaded
1.85mm (V)	67 GHz	50 Ω	0.2 W	Threaded
1.0mm (W)	110 GHz	50 Ω	0.1 W	Threaded

Common Questions

Frequently Asked Questions

Why perpendicular?

Angled cut: air gap at dielectric, connector seat failure, impedance change (50→55Ω), center conductor protrusion issues. Semi-rigid: burrs prevent connector. Full circumferential outer conductor contact requires square cut.

Tools?

Rotary (flex coax), die (hardline), abrasive (large corrugated), tube cutter (semi-rigid). Never scissors or diagonal cutters. Always deburr outer conductor. Use cable-specific tool for best results.

Cut length?

Routing distance + service loops (0.3-1m per end) + connector take-up (15-25mm per end). Phase-matched: account for Vf, ±1mm. Cut slightly long. Mark with square and tape before cutting.

Related Terms

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