Mobile HF Installation – Part 2/4 (Bonding and Choking)

This article will cover the second phase of our Mobile HF project – bonding and grounding.The following is a summary of the phases of the project:

• Phase 1 – Install the Icom IC-7000 running barefoot with a simple MFJ HAMStick Antenna (to be replaced with the Scorpion Screwdriver Antenna in Phase 3)
• Phase 2 – Properly bond all elements of my truck and deal with any noise issues (this article)
• Phase 3 – Install the Scorpion Screwdriver Antenna and Controller
• Phase 4 – Install a 500w Amplifier, 160m capability and operating accessories

We have been having fun with our new Mobile HF installation in our 2009 Ford F-150 Pickup Truck. We are currently using a simple HAMStick antennas to operate on the 20m and 40m bands. The initial installation focused on getting the radio installed in the truck and working and while this was successful, we have had to work around quite a bit of electrical noise when the vehicle is running. The noise was S9 without the Icom IC-7000 Transceiver’s Noise Blanker turned on and about S3-S4 with the Noise Blanker on. Most of the noise sounded like ignition or fuel injector spikes (it was engine speed dependent) and I understand that this is quite common with the Ford F-150 Truck. This past weekend, I set about solving the noise problems via a combination of Bonding and Choking techniques. An excellent source on how to approach this can be found on the K0BG Mobile HF website.

The first step in the process was to ground my radio to a solid point on the truck’s body. I used 3/4″ wide ground braid from DX Engineering (picture above) for this purpose. I was fortunate that my F-150 had Truck had good ground straps installed between the body and the frame at the factory (although I do plan to supplement these with heavier straps in the future).

Next, I added Type 31 choking material to the transceiver’s power and antenna leads. I added a total of three beads on the power leads (one in the engine bay close to the firewall and two on the interior side of the firewall). I also installed choking material on the antenna coax near the radio. The correct way to install these beads is to coil the cables through them as many times as possible to form an effective RF choke. With these initial steps, my noise fell from S9 to about S6-S7 without the Noise Blanker.

The next step was to bond the hood of the vehicle to the rest of the body via 1″ wide ground braid. These were made from material that I purchased from DX Engineering and they were installed on both hood hinges.

I also installed two bonding straps between the cab and the bed of the truck (one on each side).

Finally, I used kits from DX Engineering to bond my exhaust system to the frame of the truck. This needs to be done in three places – at the exhaust pipe section which is connected to the engine, on the mid-pipe which leads to the front of the muffler (shown above) and at the tail-pipe which leads from the rear of the muffler to the rear of the truck. Exhaust system bonding is probably the most effective technique for reducing electrical noise in most installation and mine was no exception.

With these additional steps, I my noise level was reduced to S0! While I still have a faint amount of engine electrical noise, I can operate without the Noise Blanker on and with a lower level of Noise Reduction than before the steps outlined here. My installation is much quieter overall and I find that I am hearing many more stations than I did before. There is still more work that I plan to do in the future including bonding the truck’s bed to the frame at all four corners, improving the existing factory grounding between the body and the truck’s frame, and bonding the four doors to the body. For now, my Mobile HF operating experience has been improved considerably.

The next stage of our Mobile HF project will be the installation of a Screwdriver Antenna. We also plan to install a mobile HF amplifier for high-power operation as well as other upgrades.

– Fred (AB1OC)