CB radio in the motorhome

Updated – December 31, 2022

CB Funk – well known to old hands, but increasingly relevant again today.

Cars, with the exception of the venerable Trabbi, usually have a solid metal roof. In the past, with mixed feelings, people drilled a central hole for the antenna base, made sure the mass was solid and enjoyed a clean standing wave.

Things are completely different for motorhomes with GRP or aluminum roofs: without a ground-free antenna, no chance.

And the antenna length, the longer the better - the reception and the range - is very limited on an already tall motorhome. 410 cm is the maximum permissible height, just think of the height control in the Elbe tunnel, for example. This usually leaves just 100 cm for a CB antenna.

At first I tried my luck with the Albrecht McKinley. Not a good idea, as it soon turned out: 2 watts measured power instead of 4 watts, modulation is very limited and cannot be improved even with a decent preamplifier microphone.
An analysis of the device revealed that no proper adjustment was made at the factory, meaning that a defective device was delivered. After correcting various settings, the device delivered the expected values.

Motorhomes with GRP or aluminum roofs lack electrical ground. The Racer 90 antenna therefore only achieved a standing wave of around 2.0. The massless one Gamma 2F however, produced a standing wave of clean 1.0. Of course, the physical propagation of radio waves with such antennas is not ideal, but it is more usable than with a bad standing wave.

If you want to achieve a decent range, both on the receiving and transmitting side, you can't avoid a base station antenna. This is difficult to achieve with a mobile home - but not impossible.

You need a stable one Aluminum sliding mast, 1.34 m long when inserted, 10 m when extended and only 9.6 kg, and a GRP station antenna that can withstand up to 500 W of continuous load, such as this Sirio Gainmaster ⅝ (data sheet) of 7.36 m long, dismantled 1.95 m and therefore just suitable for the rear garage.

Why not a GRP mast? These are too sensitive for mobile use in the long term, as the GRP pipe tends to break when the pipe clamps are tightened.
An aluminum pipe, even if anodized, is sensitive to dust and dirt particles and should therefore always be kept largely free of them.

The push mast is mounted on the rear of the motorhome above the bumper on the rear wall. The - high-quality - antenna cable is laid inside the mast tubes and at the end of the innermost tube via a Mast cap led out. This connects the prefabricated Gainmaster cable.

Internally, the antenna cable runs to one of the two inputs antenna switch, the mobile Gamma 2F is connected to the other input. This makes it easy to switch from mobile to stationary operation.

If there are two radio devices, each antenna can be connected exclusively (i.e. not in parallel) to each of the two connected radio devices using an additional antenna switch, whose two inputs are directly connected to each other via an adapter.

Tip for those who like to design and build their own antennas: in the frequency range from 50 kHz to 1.5 GHz nanoVNA 4H a recommended tool.