Ham Radio Repeater Installation: Coax, Connectors, and Feedline Guide

A ham radio repeater is a permanent RF installation that operates unattended, often for years at a time. The feedline decisions you make during installation will define the system's receive sensitivity and reliability for the life of the repeater. Cutting corners on coax type, connector selection, or weatherproofing creates problems that are difficult and expensive to diagnose later — especially when the antenna is on a tower. This guide covers the complete cable specification for a professional 2m or 70cm repeater installation.

System Overview: Every Cable Run Matters

A repeater signal chain runs from the antenna through the feedline to a duplexer, then to the receiver and transmitter (or combined transceiver). On the receive side, every dB of cable loss adds directly to the system noise figure — it makes the repeater harder to access from the edges of its coverage area. On the transmit side, cable loss reduces effective radiated power. The receive path deserves the most attention: a repeater's receive sensitivity determines its coverage far more than its transmit power does.

Why N-Type Throughout

PL-259 connectors degrade above 300 MHz. At 144 MHz (2m), PL-259 introduces measurable insertion loss and variable return loss because the connector's geometry isn't controlled at VHF frequencies. At 440 MHz (70cm), the performance is noticeably worse. For a repeater operating on either of these bands, N-type connectors throughout the signal path provide several important benefits: controlled 50-ohm geometry to 11 GHz, weatherproof mating when outdoors, threaded coupling that resists vibration, and 500W power handling at 1 GHz.

Use N-type from the antenna through the feedline to the duplexer, from the duplexer to the transceiver connections, and on all test access points. The only exception is very short jumpers inside the equipment cabinet where PL-259 is dictated by the transceiver's antenna port — use the shortest practical cable for those connections.

Duplexer Connections

Most commercial and amateur duplexers (Sinclair, TX RX Systems, DB Products) have N-female ports. The radio end of the duplexer connects to the transceiver, which typically has a PL-259 port. This short jumper — usually 1 to 3 feet — connects a PL-259 on the radio end to an N-male on the duplexer. Use RG-58 or equivalent for this short run; the loss over 2–3 feet is negligible.

Short N-Male jumpers for duplexer connections

Feedline: The Critical Run

The feedline from the duplexer (inside the building) to the antenna (on the tower or roof) is where most of the cable loss occurs. This is also the hardest cable to replace after installation — it may be in conduit, through a wall, up a tower. Specify the right cable the first time.

At 440 MHz, 100 feet of RG-58 loses 7 dB — over 80% of the received signal is gone before it reaches the duplexer. LMR-400 loses 3.2 dB — still significant, but far more manageable. LMR-600 loses 2.0 dB on the same run. For any feedline run over 50 feet, LMR-400 is the minimum. For runs over 100 feet, LMR-600 is strongly recommended.

LMR-400 N-Male to N-Male Feedline  |  LMR-600 N-Male to N-Male Feedline

Power Handling

LMR-400 handles approximately 700W at 150 MHz. LMR-600 handles approximately 1100W at 150 MHz. At 450 MHz, these figures drop to about 450W and 700W respectively. These ratings are adequate for virtually all repeater installations — most club and commercial repeaters operate at 25–100W transmit power. Power handling is rarely the limiting factor in coax selection; loss and receive noise figure are far more important in repeater design.

Lightning Protection: Not Optional

Install a gas-discharge lightning arrestor at the building entry point on every outdoor feedline. Period. This is required by NEC 810, recommended by ARRL, and required by most repeater coordination bodies. The arrestor should be a type rated for the operating frequencies — PolyPhaser IS-B50LN-C2 is widely used in amateur repeater installations for 2m and 70cm.

The arrestor mounts on the outside wall, inline in the feedline, with its ground lug bonded directly to the building's main ground system via #6 AWG or larger copper conductor. A ground rod driven separately near the building entry is not a substitute for bonding to the main ground system — it creates a ground potential difference during a strike that can damage equipment. Bond everything together: tower ground, cable shield ground, building entry arrestor, and utility ground.

Weatherproofing

Every outdoor N-type connection needs weatherproofing. Self-amalgamating tape applied in two layers over the mated connector pair provides the primary seal. Apply from below, working upward and over the connector body. On the antenna feedpoint — typically the most exposed connection in the system — use coax seal (Coax-Seal or equivalent) applied to the threads before mating, followed by self-amalgamating tape, followed by UV-resistant vinyl tape. Inspect outdoor connections annually and re-seal any that show cracks or discoloration.

Create a drip loop at the building entry: the feedline should curve down before entering the wall, so that water runs off the cable rather than following it into the wall penetration. This simple measure dramatically extends the service life of both the cable and the building penetration seal.

Cable Labeling

Label both ends of every cable run before installation. A dymo label or a printed cable tag, wrapped in UV-resistant tape, should include: cable type, length, installation date, and what it connects (e.g., "LMR-400 — 85ft — Duplexer TX Port to Antenna — 2025-03"). This information is invaluable five years later when the repeater develops a problem and you're standing in front of the equipment cabinet trying to remember which cable goes where. This is standard practice in commercial RF installations for exactly this reason.

Transceiver to Duplexer Adapter Cables

When the transceiver has a PL-259 port and the duplexer has N-female ports, use N-to-PL-259 jumpers. Use the shortest practical length — 2 to 3 feet is typical inside an equipment cabinet.

RFC400 N-Male to PL-259  |  RFC400 N-Male to N-Male

Testing After Installation

Before transmitting through the complete system, verify SWR at both ports of the duplexer using an antenna analyzer or VNA. Target SWR of 1.2:1 or better at the operating frequency. SWR above 1.5:1 after a new installation indicates a problem: check for cross-threaded connectors, verify cable is not kinked, verify the antenna is properly assembled, and verify you haven't accidentally used 75-ohm cable anywhere in the run. High SWR on a repeater that was previously working is almost always water ingress into a connector or a mechanically damaged cable — disconnect and inspect each connection systematically.

After the install checks out, monitor the repeater from the fringe of the expected coverage area. The goal is that users on the edge of coverage can access the machine consistently. If coverage is disappointing, cable loss is the first thing to address — it's the most impactful improvement available to an existing installation short of changing antennas.