External Antenna Wiring Specification for the GNSS Anti-CRPA System TX02: Getting the RF Front-End Right

The GNSS Anti-CRPA System TX02 is only as good as the signals it receives. And those signals travel through cables — coaxial cables that connect the CRPA antenna array on the roof of a vehicle or the mast of a vessel to the TX02 processing unit inside. If those cables are wrong, too long, poorly terminated, or routed near interference sources, the entire anti-jamming chain falls apart.

Wiring the external antenna is not a detail. It is the foundation of the system. Getting it wrong means degraded beamforming, false jammer detection, and positioning errors that no amount of software processing can fix.

Why Antenna Wiring Is the Most Critical Installation Step

Most installation guides spend pages on software configuration and almost nothing on the physical RF cabling. That is backwards. The TX02 processes signals that have already been degraded by the time they reach the unit. Every decibel of loss in the coaxial run, every millimeter of phase mismatch between elements, every ground loop introduced by poor cabling — all of it shows up as reduced jamming suppression capability.

A CRPA antenna works by comparing the phase and amplitude of signals arriving at each element. The TX02 uses those comparisons to steer nulls toward jammers and maintain lock on satellites. If the cables introduce uneven phase shifts, the TX02's beamforming algorithm receives corrupted input data. It will either fail to detect a real jammer or steer a null in the wrong direction, accidentally blocking a satellite signal instead of the threat.

This is why the wiring specification for the TX02 external antenna is not a suggestion. It is a hard requirement.

Coaxial Cable Selection and Phase Matching

Choosing the Right Cable Type for GNSS L-Band

Not all coaxial cable is created equal. The TX02 operates across GNSS L-band frequencies — GPS L1 at 1575.42 MHz, L2 at 1227.60 MHz, L5 at 1176.45 MHz, plus GLONASS, BeiDou, and Galileo signals in the same range. At these frequencies, cable loss matters enormously.

Use phase-stable, low-loss coaxial cable rated specifically for GNSS applications. RG-402 or its equivalent is the standard choice. It offers attenuation of roughly 1.5 dB per 10 meters at 1.5 GHz, which is acceptable for runs up to 15 meters. Do not use RG-58, RG-174, or any cable not rated for L-band. Their loss at 1.5 GHz exceeds 5 dB per 10 meters, which means a 5-meter run would eat 2.5 dB of signal before it even reaches the TX02. That is signal you cannot afford to lose.

The cable must also be phase-stable. This means the electrical length of the cable does not change significantly with temperature or bending. Standard coaxial cable changes phase with every degree of temperature shift. For a CRPA system where phase coherence across elements is everything, this is unacceptable. Use cables with a solid dielectric core, not foamed dielectric, for the short runs between antenna and TX02.

Length Matching Across All Antenna Elements

Every cable running from a CRPA antenna element to the TX02 input must be the same electrical length. Not approximately the same. Exactly the same. A mismatch of even 5 millimeters introduces a phase error of roughly 10 degrees at L1 frequency. That sounds small, but it is enough to degrade the CRPA's null-steering accuracy by several degrees.

Measure each cable run with a time-domain reflectometer (TDR) before installation. Trim cables to match within 1 millimeter. Mark each cable with its element number and length so you never mix them up during re-termination. In the field, a swapped cable means a phase-matched array becomes a random array, and the TX02 cannot do its job.

RF Connector Termination and Grounding

Proper Connector Crimping and Soldering Technique

The connection between coaxial cable and RF connector is where most installations fail. A poorly crimped connector introduces impedance discontinuity that reflects signal energy back toward the antenna. This creates standing waves that distort the amplitude and phase data the TX02 needs for beamforming.

Strip the cable jacket carefully. Do not nick the dielectric. Do not leave the center conductor exposed more than 2 millimeters beyond the connector body. An exposed center pin acts as a parasitic radiator and picks up interference from nearby electronics. For ground vehicles, this means engine noise. For marine vessels, it means radar emissions.

Use precision crimping tools rated for the connector type. Do not use pliers. After crimping, inspect the termination under 10x magnification. The center conductor must be perfectly centered. The dielectric must sit flush against the connector shoulder. Any offset creates an impedance mismatch that degrades signal quality.

Solder the connection only if the connector manufacturer requires it. For most GNSS-rated connectors, a properly executed crimp is sufficient and actually performs better than a solder joint because solder can wick into the dielectric and change its electrical properties over time.

Grounding the Antenna Feed Lines

The coaxial cable shields must be grounded at the TX02 end — and only at the TX02 end. Grounding at both ends creates a ground loop. Current flows through the shield, generating a magnetic field that couples into the center conductor. This shows up as low-frequency noise in the GNSS band.

Use a single-point ground strap from the TX02 chassis to the platform's main ground plane. The ground strap should be short, wide, and made of tinned copper. Do not use a thin wire — its inductance defeats the purpose at GNSS frequencies.

On vehicles with composite bodies, run a dedicated ground wire from the TX02 ground point to the metal chassis frame. Do not rely on the vehicle's body panels as a ground path. Composite materials do not conduct, and any paint or coating adds further resistance.

Cable Routing and EMC Best Practices

Separating RF Cables From Power and Data Lines

Run the antenna coaxial cables in a dedicated conduit or cable tray, separated from DC power cables by at least 10 centimeters. If 10 centimeters is not possible due to space constraints, maintain a minimum of 5 centimeters and cross any power cables at 90-degree angles. Parallel runs create inductive coupling that injects noise into the RF signal.

Keep the coaxial cables away from the vehicle's CAN bus harness, Ethernet cables, and any high-frequency data lines. The TX02's RF front-end is extremely sensitive. A CAN bus cable running parallel to a GNSS feed line for even 30 centimeters can induce enough noise to raise the system's detection threshold and cause it to miss low-power jammers.

Use cable ties with non-metallic clips to secure the coaxial runs. Metal cable ties create an unintended ground path and can detune the cable shield.

Weatherproofing the External Connections

On marine vessels, every external RF connector must be weatherproofed with heat-shrink tubing and silicone sealant. Saltwater corrosion destroys connector contacts within weeks if left unprotected. Use marine-grade connectors with gold-plated center contacts. Gold does not oxidize, which means the connection quality stays stable over years of exposure.

On ground vehicles, the connectors on the roof-mounted CRPA array must be sealed against dust and moisture. Use self-amalgamating tape over each connector, then cover with a silicone boot. This is not optional in desert or arctic environments where temperature cycling causes sealants to crack.

Verifying the Wiring Before System Activation

TDR Testing and VSWR Measurement

Before powering on the TX02, run a TDR sweep on every coaxial cable. You should see a clean impedance curve with no reflections. Any bump or spike in the TDR trace indicates a bad connector, a cable kink, or an impedance mismatch that must be fixed before the system goes live.

Then measure the Voltage Standing Wave Ratio (VSWR) at each input port. A VSWR above 2.0:1 at any frequency in the GNSS L-band means excessive reflection loss. Re-terminate that connector or replace the cable. The TX02 cannot compensate for a bad antenna feed.

End-to-End Signal Path Validation

With the TX02 powered on but the CRPA calibration not yet started, inject a known GNSS test signal at the antenna feed point and measure the signal level at the TX02 input. Compare this to the expected loss based on cable length and type. If the measured loss exceeds the calculated loss by more than 1 dB, you have a problem in the cable run — likely a connector issue or a section of damaged cable.

Fix it now. Do not proceed to calibration with a marginal signal path. The calibration routine will compensate for minor variations, but it cannot overcome a fundamentally broken RF connection.