Going Mobile

The Who had a hit tune entitled Going Mobile that may be playing in your head right now.  While the song celebrates the joy of living in a mobile home and traveling caravan-style in the UK, going mobile to hams means using radio equipment in your vehicle.

While some hams have HF radio setups in their cars, mobile predominantly means local VHF/UHF communication.  Besides bring able to talk to our ham buddies while driving around, 2m/70cm capability is particularly useful in case of disaster or other emergency communication (EmComm) situations.  It is perfect for storm spotting and certain public service events.

Mobile operation is popular and important enough that there are a number of US license exam questions involving the topic as you will see below.

Installing and using amateur radio equipment in one’s personal vehicle is too large a topic to cover here so we’ll simply advise you to research details on your own.  Talk to fellow hams and see what/how/why they installed their own gear.

The internet is also a vast resource for [mostly good] info .  One noteworthy site dedicated to mobile ham operation is managed by Alan Applegate, K0BG, and is located here.   It contains exceptionally useful info on most topics presented below.  We encourage you to use this site as a primary reference for your own mobile radio installation and operation.  The ABCs topic is the best place to start.

Before embarking on any of this yourself, there are several important points to consider:

  • Radio type
  • Radio control location
  • Radio mounting
  • Radio power wiring
  • Antenna type and mounting
  • Radio audio/speaker
  • Transmitting while driving
  • Hands-free/Distracted driving laws
  • Noise and interference

We will scratch the surface of each of these topics here:


Radio type-  Choose a mobile radio that best fits your needs, desires, and budget based on several factors:

  • Brand– quality/reliability and/or familiarity/loyalty
  • Transmit power (Watts)
  • Features– Auto power-off, APRS, dual-channel, remote head, cross-band, packet
  • VHF/UHF (V/U) or HF?
  • FM only, or multi-mode?
  • Single-band, dual-band, tri-band, or quad-band?
  • Analog or digital communication, or both?
  • New, reconditioned, or used?

Note that while a hand-held transceiver (HT) can be used in a car, it is significantly limited by its antenna and transmit power.  Both can be improved (linear amplifier and external antenna) but if you really want good mobile performance you should consider a purpose-specific mobile radio.


Radio control location-  Modern mobile transceivers typically feature removable front panels where the operator controls can be positioned in a more convenient, ergonomic, and safe location using a smaller footprint.

A thin separation cable links the control panel to the main radio chassis, which can then be located elsewhere in the vehicle.  So the display, buttons, and knobs can be installed to best suit the radio operator in their particular car.

Control mounting options are plentiful.  DIY or buy specialized mounts.  You can find many varieties of commercial front panel mount variations: vent clip, cup holder, bolt down, adhesive, suction cup, and more.

The seat bolt one is very interesting because it doesn’t alter the vehicle, allows the controls to be well-positioned for the driver, and doesn’t interfere with passenger comfort.  A couple of photos of one such installation are shown below:

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Goose neck mount is secured to floor using existing seat bolt

Not promoting any particular manufacturer but here is a link to a variety of mounts.

Installation should also be secure so that it doesn’t fly around the cabin in event of a crash.  Always consider air bags when locating radio controls.  You don’t want to mess with sensors when installing or have a bag deployment impale you with radio parts in a collision.


Radio mounting-  Primary concern is locating the main radio body in a well-ventilated area away from direct sunlight and, of course, so that it doesn’t interfere with safe operation of the vehicle.  The five obvious choices are:

  • Under dash, with controls (traditional)
  • Under dash, remote controls
  • Under seat, remote controls
  • In trunk, remote controls
  • Passenger side front console, remote controls

The radio chassis should be secure, as should the associated wiring, which must also be routed to avoid interference with driver control.  Mobile radios tend to run hot and require significant air flow.  Use the factory-supplied mounting bracket if possible.


Radio power wiring-

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No matter where your mobile radio is located in the car it is always best to wire its power directly to the vehicle’s 12VDC battery.  This is mainly to prevent dangerous overloads to existing vehicle wiring.  It also minimizes nuisance noise and interference issues, plus permits the radio to be used when the engine is not running (many potential power circuits are switched through the ignition key).

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The K0BG site previously mentioned has an important page on power wiring that is a real eye-opener on this very topic.  Alan clearly communicates to “Never, ever use existing vehicle wiring to power any amateur radio gear. This includes fuse taps, and so-called accessory sockets, aka cigarette lighter sockets!”, and explains the rationale for avoiding this practice.  For convenience we will link it here.

That said, we have no issue with using an accessory power socket for short-term (temporary) use with a 50W max. transceiver provided that the outlet’s fuse and wiring are sized appropriately (e.g., 15A fuse/wire combo for 9A peak radio load).

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Temporary 50W radio power via 180W socket with 15A vehicle fuse & wiring.

There are further considerations for modern vehicles with battery monitoring systems and/or electrical load monitors.  The same K0BG Wiring & Grounding page includes helpful info on the subject.


Antenna type and mounting-  Antenna type is fundamentally determined by the desired operating bands:

  • HF antennas generally get large and complicated.
  • Single- or dual-band V/U antennas are simple vertical whips with minimal size and mounting concerns.  By far the most common in ham radio.
  • Tri- or quad-band antennas are fairly simple but longer and more unsightly than dual-band ones.

Mobile HF antennas are a complex topic and are less common among mobile hams.  We will limit our discussion here to V/U mobile antennas and mounts.

Two choices to make: wavelength and mounting thread.  5/8-wave antenna is considerably longer than 1/4-wave but will give better performance in suburban and rural areas.  For big cities or mountain communities where repeater antennas are very high, the 1/4-wave antenna favors high radiation angles.

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The mounting thread selection should match your antenna mount.

Mobile antenna mount choice is important.  In general, quality of the ground plane (solid metal, contact resistance, area, uniformity) affects antenna gain and radiation pattern.

Mobile antenna mounts include a length of coaxial cable.  Specify connector type to match radio or use an adapter.

The three most common types of mobile V/U antenna mounts are: Permanent, Magnetic (mag mount), and Lip or Bracket.

Permanent mounting gives superior performance when centered and properly installed.

Permanent mount involves drilling at least one hole in the roof (best) or trunk lid of the vehicle.  Not all hams are willing to do this.

Magnetic mounting does not provide direct contact with counterpoise (roof or trunk); it is capacitively coupled so not as efficient.

Small magnets may not stay in place at high vehicle speeds.  Recommend 3½” size minimum.

Mag mounts will almost certainly damage the vehicle’s surface underneath them.  They also become projectiles in case of a vehicle crash (insurance and liability factor).

Recommended for temporary use only, although some hams are happy with their permanently installed mag mounts.

Lip or bracket mounts give better contact to the ground plane than mag mounts.  However, they usually locate the antenna away from the center of the vehicle due to their edge- or side- attachment method.

For true omni-directional radiation, the antenna should be centered over a large metal surface.  Avoid mounting near edges.

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Window glass mount antennas exist but are essentially useless so we won’t discuss them here.

Other antenna considerations are power handling capability and “gain”.  You’re unlikely to be running more than 75W mobile transmit power; in case you are, pay special attention to this spec.  Antenna gain is a weird subject anyway (see our topic here) and manufacturer performance claims should be carefully scrutinized.

In summary, your mount choice is a significant factor in antenna performance.  Permanent mounting centered over a large metal surface gives superior results.

Much of this info comes from our post entitled, Understanding Antennas-A Simplified Perspective.  Mobile antenna detail is on slides 98-104.


Radio audio/speaker

Is the internal radio speaker adequate?  This depends on where the main radio chassis is located and how quiet the interior of the vehicle is.

If you can’t hear the audio, you can wire it to a separate speaker, or connect to the vehicle’s audio system aux input.

As with all other mobile equipment installations, a speaker must be securely attached and in a safe location.


Transmitting while driving-  Pay special attention to the road while fiddling with controls or speaking into the microphone when you are driving.  It’s easy to get distracted with the radio and you could get into real trouble by losing control of your vehicle.

It’s always best to pull over to transmit, or do so only when the vehicle is parked or otherwise not in motion.


Hands-free laws

Distracted driving or hands-free laws are becoming commonplace at the state and local government in the USA.  While some statutes specifically exempt amateur radio operation from enforcement, the average police officer may not make the distinction.  You may be OK legally but still experience the hassle of being cited.

Simply be aware of laws in your area or where you may travel and be prepared to deal with enforcement.


Noise and interference-  Mobile radio operation has its own issues with noise and interference.

Noise in the cabin can be picked up by the microphone from unusually loud engines, tire-road combinations and wind rushing in from open windows or air vents blowing at max flow.  Any of these can make it difficult for your audio to be heard clearly.  Once again this situation is improved by transmitting only when the car is not in motion.

In a car there are a number of sources for electrical noise and/or interference that can disturb a received radio or audio signal, or make your transmission hard to copy at the other end.  The car’s alternator is a frequent culprit, long with fuel pumps & other small motors, and vehicle control computers. Modern vehicles have more integrated electronics and displays with noisy backlight inverters, all potential sources of e-noise.

Note that FM mode is more immune (but not completely) to electrical noise so there are fewer noise issues with the more common V/U mobile radio use.

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Also be aware of a phenomenon where your signal may sound fluttery while in motion due to rapid signal changes (obstructions, reflections, multi-path).

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Hopefully this post gave you some points to ponder and helps guide you toward successful mobile radio installation and operation.

 

One thought on “Going Mobile

  1. For some of us mobile means bike or on foot. That means HT’s and extra battery packs. Or one kept in a backpack, or even two in the backpack. I’m on 2m, 70cm and on DMR. KD1S

    Like

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