23 Oct 2014 – Practical HF Mobile

How one person, over the years, installed and tested a number of HF mobile transceiver was the subject of the talk given by Dave, G4ETG.

The first warning was to check the manufacturer’s manual to see what power levels they suggest shouldn’t be exceeded and where best to mount an antenna for VHF or HF.  Dave has found that most modern cars use a CAN-Bus wiring system that not only makes the power connections but also supplies data to the car’s electrical control system, including engine management, power windows, lights, in fact, everything electrical.  This system using just two wires can eliminate the need for up to 2km of the conventional old style car wiring!

Dave explained that using conventional mobile phone mounts he was able to mount a modern HF radio head on the dash and since he seldom has back seat passengers,  was able to put the body of the transceiver under the front seat. Of course, any item mounted on the dashboard needs to be out of the way of any possible air bag deployment!  To minimize noise pick up, the radio wiring was routed on the side of the car that didn’t have the main wiring. Since almost all hinges are painted they require bonding to ensure the entire body shell is electrically connected, which includes the exhaust, since on a large car can be almost a quarter wave on 20m!

After the installation, extensive testing on all bands, while stationary and moving,  will point out any interruptions or unexpected changes to the car’s normal operating systems and give an indication of noise experienced on the HF radio which may need further work.

As a way of indicating if all this was worth it, Dave explained he had made contacts with Tasmania on 40m as well as 20m contacts with Japan and the west coast of America!