Campervan Ham Radio: Antennas, Power and Noise for Motorhomes
A van or a motorhome is a good radio shack on wheels. It has its own battery, a roof for the antennas, a table, and the freedom to park on a hill, by a lake or in a field far away from the electrical noise of a town. Many amateurs combine travelling with the hobby, and campervan ham radio has become a distinct branch of portable operating, with its own tricks and its own problems. The same metal box that carries the antenna also carries a solar charger, an inverter, a refrigerator compressor and a dozen small electronic devices, and they can fill the band with noise. This guide covers the main decisions: what to operate and when, which antennas work on a vehicle, how to bring power from the battery to the radio safely, and how to keep the noise down.
Decide What You Want From the Van
The design depends on how you intend to use the radio. There are two styles that need different solutions. In the first the vehicle is parked, and you operate from a table or a bed for an hour or a whole evening, with a wire antenna thrown into a tree or a telescopic pole attached to the side. In the second you want to talk while you drive, on VHF and UHF, with a fixed antenna on the roof, a radio under the dashboard and a microphone within reach. Many people do both, and this is possible, but the equipment should be chosen with the main use in mind. A large HF antenna that can be used on the move is rarely a good idea in a vehicle with a low bridge or a branch above, and a parked station can use bigger and better antennas than any that you would mount on the roof. Our general article on mobile HF installation covers the same issues for a car, and the van adds more space, more power and more noise.
The rules deserve a thought as well. Operating while driving is regulated differently in each country, and holding a microphone in your hand can be an offence even where radio use is permitted. The identification in the case of mobile and portable operation is described in our guide to portable call sign suffixes. For the HF bands, the sensible practice is to operate when you are parked and to use the VHF radio on the road with a hands-free microphone.
Antennas on a Vehicle
The body of the vehicle is a part of the antenna, because it provides the counterpoise or the ground plane for a vertical. A metal roof is an excellent ground plane for a VHF or UHF antenna, and a quarter-wave whip on an NMO mount in the middle of the roof gives a clean omnidirectional pattern. The glass fibre roofs and bodies that are common on modern motorhomes are not conductive, and for these a mount with a small ground plane or a different design is necessary. Magnetic mounts work only on steel; they do not hold on aluminium or on plastic, and a roof rack or a ladder can change the match.
| Antenna | Best use | Strengths | Weak points |
|---|---|---|---|
| VHF and UHF whip on an NMO mount | Driving and parked, repeaters and simplex | Small, low drag, good ground plane on a metal roof | Needs a hole or a clamp mount; weak on a glass fibre roof |
| HF whip or screwdriver antenna on a bumper or ladder | Parked and driving, several bands | Fast to switch bands, fixed in place | Short antennas have low efficiency, and height is a limit |
| End-fed half-wave on a telescopic pole | Parked, HF multiband | Efficient, cheap, easy to set up | Needs a few minutes and a support |
| Wire dipole or inverted V from a mast | Parked, best HF performance | Excellent efficiency, quiet away from the van | Needs a campsite with space and trees |
| Magnetic loop | Parked, limited spaces | Compact, directional nulls reduce noise | Narrow bandwidth, needs retuning |
For parked HF operating the easiest and most efficient solution is an end-fed half-wave on a telescopic pole, fixed to the van or a rack and sloped out to a tree or a stake. It needs no ground plane, and it can be put up in five minutes. An inverted V on a pole is even better for 40 and 20 meters, and it keeps the radiating part of the antenna away from the noise sources of the vehicle. A short antenna mounted on the vehicle always suffers a loss in efficiency, as the efficiency of any antenna that is short in wavelengths shows, and the van is a poor ground plane for the low bands.
Power From the Battery
A 100 watt HF transceiver draws about 20 to 22 amperes at full output from 12 volts, and a 50 watt VHF and UHF radio draws about 10 to 12 amperes on high power. These currents need proper wiring. The common rule is to connect the radio with a short run of thick cable to the battery, using a fuse close to the battery in the positive lead. A 10 AWG cable, which is about 5 square millimetres, with a 25 ampere fuse suits a 100 watt radio on a run of up to 3 metres. For longer runs use thicker cable, because the voltage drop in the wires lowers the power and can cause the radio to reduce its output. The lithium iron phosphate battery that many vans use as a house battery has a nominal voltage of 12.8 V and holds it well under load, which makes it a good source for a radio. The principles of choosing and wiring a source are discussed in our article on battery power for portable operation.
- Use the house battery, not the starter battery. A radio that drains the engine battery can leave you stranded.
- Fuse both the power lead and the branch. A short circuit in a thick cable can start a fire. Put the fuse as close as possible to the source.
- Keep the cable short and thick. The drop in voltage matters more than the cost of copper.
- Use proper connectors. Crimped ring terminals and good Powerpole or similar connectors are better than clips.
- Check the battery protection. A battery management system may cut off at a low voltage, and this can drop the radio in the middle of a contact. Know the limit and watch the level.
The Noise Problem
A van is full of electronics, and most of it was designed without a thought for the HF bands. The worst offenders are the solar charge controllers, the inverters, the DC to DC converters, the chargers for phones and laptops, the LED lights and the compressor of the refrigerator. A maximum power point tracking controller, usually called an MPPT, switches large currents at a high speed to extract power from the panels, and its harmonics can reach well into the HF bands. The result is a rising noise floor with lines of birdies every few kilohertz, which can be worse at midday when the sun is brightest.
The way to find the sources is the same as for a house: turn everything off, listen with the radio, then switch on one device at a time. The detailed method is described in our article on finding and killing RF noise. In a van the usual measures are the following.
- Switch off the guilty device while you operate. The solar controller can be turned off for an hour, if the battery has enough charge; the inverter should be off when it is not needed.
- Put clamp ferrites on the DC leads and the panel cables. Use several turns through a large core near the device.
- Increase the distance. Mount the antenna as far as possible from the controllers and the cable runs, and run the coax away from the power wiring.
- Use a different supply for the radio. A direct line to the battery, away from the other loads, reduces the noise on the supply.
- Replace the worst devices. Cheap switching adapters are a typical cause, and a better one may be quiet.
- Operate away from the vehicle. A wire antenna 20 or 30 metres from the van can lose the noise almost completely.
Feedline, Bonding and Mounting
The coaxial cable is the part that is easy to forget. Route it from the antenna to the radio along the shortest path that does not touch the power wiring, and avoid running it next to the solar cables or the inverter. Seal the place where it enters the body, and leave a drip loop so that water does not follow the cable inside. For an antenna that uses the vehicle as a counterpoise, bond the mounting point to the body with a short, wide strap, because a poor connection to the metal makes the antenna lossy and noisy. Where roof panels are joined by rubber seals or paint, the electrical contact may be poor, and a braid strap between the panels helps. For a bumper or ladder mount, scrape the paint from the contact area and protect the bare metal with a grease or a sealing compound. A good mechanical design is as important as the electrical one: an antenna on a moving van must withstand wind, vibration and low branches, so use a strong mount and check it before every trip.
RF Safety and Neighbours
A transmitting antenna on a vehicle is close to people, and the distance to the antenna matters. Keep the power appropriate, keep people away from the antenna when you transmit and place the antenna so that nobody can touch it. The recommendations on safe distances are in our guide to RF exposure and safety. At a crowded campsite your neighbours may be only a few metres away, and a transmission can disturb their television or radio. Use a modest power, choose bands with little risk of interference, keep your operating at a decent hour and be willing to stop if somebody complains. A friendly word at the start of the stay does more for the reputation of the hobby than any technical measure.
A Simple Starter Setup
If you are building the system from nothing, a sensible order is as follows. Start with a dual-band VHF and UHF mobile radio and an NMO antenna on the roof, with a fused lead to the house battery. This gives local contacts, the use of repeaters, and an easy introduction to the operation in the vehicle. Then add a compact HF transceiver of 20 to 100 watts for parked use, with an end-fed half-wave antenna and a telescopic pole, and carry a ferrite choke for the feedline. Test the system at home, in the driveway, with the solar controller on and off, and write down which devices make noise. Finally, practise putting up and taking down the antenna, because speed and tidiness are what turn a good idea into an enjoyable routine on the road.
The Bottom Line
A campervan makes a convenient shack, but it needs planning. Choose a VHF and UHF whip on a roof mount for driving and a wire or end-fed antenna on a pole for parked HF operation, because a short antenna on a vehicle is inefficient on the low bands. Power the radio from the house battery with thick, short, fused cable, allowing about 20 amperes for a 100 watt transceiver. Look for noise from the solar controller, the inverter, the converters and the chargers, and cure it with ferrites, distance and switching off the offender. Keep people away from the antenna, respect the rules on mobile operation and your neighbours, and test everything at home before you travel.
Frequently Asked Questions
What is the best antenna for a campervan?
For VHF and UHF, a whip on an NMO mount on the roof. For HF, an end-fed half-wave or dipole on a telescopic pole when parked, since short vehicle antennas are inefficient on the low bands.
Can I use a magnetic mount on a motorhome?
Only if the roof is steel. They do not hold or work on aluminium or glass fibre roofs, where a clamp or a mount with its own ground plane is needed.
What size wire and fuse for a 100 watt radio?
About 10 AWG cable, around 5 square millimetres, with a 25 ampere fuse near the battery, for runs up to about 3 metres. Use thicker wire for longer runs.
Why is my radio noisy when the sun is out?
The MPPT solar charge controller switches large currents at high speed, and its harmonics can reach the HF bands. Add ferrites, move the antenna away or switch the controller off while you operate.
Can I operate HF while driving?
It is possible with a mobile antenna, but laws on distraction and on the use of handheld microphones vary. Park to operate HF, and use a hands-free setup for VHF and UHF.
Should I power the radio from the starter battery?
No. Use the house battery so that a long session does not leave you with a vehicle that will not start.