VE6AB Mobile Ops

Your Mobile and Bonding

If you have recently installed an HF rig in your mobile along with an antenna or are planning to, it is important that you realize that the antenna is only one half of a dipole, and in the case of a mobile antenna the missing half is the vehicle and its capacitance to the ground under the vehicle.

The single biggest factor with respect to efficiency for any mobile and especially on 40 and 80 meters is ground loss, so maximizing this half of the antenna system is essential, and this is accomplished through bonding.

After finishing the install, you possibly have found out that your experiencing engine noise on the receive side of your rig.

You will find that you can eliminate a lot of the noise with the use of ground straps to bond the various panels that make up the body of your mobile.
Besides the various body panels that you will want to bond, the biggest culprit of noise generation in a vehicle may be the exhaust system.

The majority of vehicles have injectors and spark plug coils in place for each cylinder. These devices can create substantial pulses on the vehicle wiring, acting against the ground system. Engine blocks often have a poor ground, so anything attached to them can radiate noise. The exhaust system is directly bolted to the engine and can behave just like an antenna, radiating noise.

After initially installing the HF gear in my mobile, I found that I was experiencing some engine noise.
I was sure that grounding the exhaust system would rid me of the some of my problem with noise, and this proved to be the source of the noise that I was experiencing in the receive side of my HF rig.

I believe the photo speaks for itself, as you can see the U-Clamp that I installed around the exhaust-pipe at the rear of my mobile, and then fastened a flat-braid ground strap between the U-Clamp and the frame. I installed another U-Clamp and ground strap at the engine end of the exhaust system as well.

This proved to be where the noise was being generated, and I now have a noise free receiver.

For any bonding you do to your mobile, it is important that you use flat braided straps and not round wire for bonding, as RF travels on the surface rather than through the wire, therefore flat braid has more current carrying capacity due to its larger flat surface.

Another way although not as simple to install, is the use of wide flat copper flashing like a friend of mine used for bonding his mobile.

It is important that you keep all of the ground straps as short as possible, and if you cannot use existing body fasteners, do take care when drilling holes in the body, so that you do not drill in-to any existing electrical harnesses that may not be visible.
I used quality stainless steel fasteners along with stainless steel serrated washers for attaching the ground straps throughout my mobile.