Project Considerations

by John KI7LYP on 2020-08-05

A great COVID-19 project might be the installation of a new mobile radio, or to inspect and do some maintenance on an existing installation!

Installation Items to Think About

  • Never use existing vehicle wiring to power any amateur radio gear. This includes fuse taps and accessory sockets!
  • Factory-supplied 120 volt inverters may cause RFI, and arcing can occur between the springloaded tip of the accessory socket plug and the positive contact inside the socket.
  • Solid wire should never be used in a mobile installation. This includes CAT5 cable often used as a less expensive alternative to factory-supplied, modularized cables.
  • Most mobile transceivers operate on 13.8 VDC. If the voltage drops much lower than 12.2, most transceivers will simply shut off or have lower power and transmission quality issues. Use of #12 gauge wire will work for most installations and prevent voltage drops.
  • Twist-on wire nuts should never be used as a splice.
  • One of the most important requirements for secure terminations, is using the right crimping tool.
  • Using the wrong size terminals such as #12 terminals for #18 wire is a common error. Use the correct size and try to use ring connectors.
  • All connectors should be both crimped and soldered to insure strength and low resistance connections. Try to avoid butt connectors.
  • Insulation temperature rating of vehicle wiring should be at least 90°C (195°F) in the passenger compartment, and 105°C (220°F) in the engine compartment.
  • All exposed wire should be covered with protective split loom.
  • Abrasion resistance is also important. XLP and PVC insulation materials are both acceptable, if they’re rated at the correct temperatures.
  • Correctly installed wiring should be out of sight, protected from abrasion and sharp edges, and positioned in such a way as to eliminate hazards and interference from or to vehicle wiring and controls.
  • Do not use vinyl electrical tape to secure the cables. Although the vinyl may not fail, the adhesive eventually becomes elastic which allows the tape to unwrap.
  • All wiring should be secured to prevent vibration damage to the insulation and/or connection points.

Power Connection Concerns

  • Some aluminum-bodied vehicles require special installation practices with respect to galvanic corrosion. Check the factory recommended installation procedures.
  • Preferably connect the positive power to the positive battery terminal and the negative lead to the same chassis grounding point as the battery’s chassis ground point and not to the battery negative terminal.
  • The negative lead fuse should not be removed. If the grounding point should lose its integrity, excessive current could flow through the transceiver’s negative lead.
  • It should be noted that, in some cases, the battery’s chassis grounding point is inaccessible. If this is the case, attach the transceiver’s ground connection as close as possible.

Maintenance Items to Consider

  • Time, dirt, and oxidation can cause connections to increase in resistance, which increases the voltage drop, so part of routine maintenance should include removing and reinserting fuses, power pole splices, and even transceiver-mounted power connectors.
  • There will always be some level of common mode current flow in any mobile installation. Poor antenna mounting techniques (mag and clip mounts) and locations (trailer hitch and bumper mounting) increase the level and proper choking of these currents must be applied.
  • Twisting the positive and negative power leads together to enhance noise immunity and/or cure alternator whine and/or cure ignition and RFI are myths.
  • Your transceiver fuses are normally ATC style, while most automotive fuses are ATO style.

Terminal Blocks

If possible, consider installation of a terminal block such as the RigRunner 4005. Connect the terminal block to the battery and battery chassis ground, and remember to fuse both leads. Now you have several power pole connection points in your vehicle to attach radios and other devices. Excess cabling should be shortened as required.

Unfortunately, some amateurs just can’t bring themselves to cut up a factory power cable. If you need to extend the cable later, take that cutoff piece (you did save it because you’re a typical ham, right?), apply power pole connectors to it, and you’re back to a full-length cable.

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