Over the past few years, a lot of attention has been developed regarding grounding and bonding. I am pleased that my ARRL book Grounding and Bonding for the Radio Amateur has generated a lot of interest. This is a very important subject for hams as they build stations, install new equipment, and troubleshoot various problems, particularly RF interference or RFI. However, as I observe and take part in online conversations, it is clear that confusion exists about ground connections, bonding of equipment, and their effects on RF and RFI.
This short article focuses on grounding and bonding when dealing with RFI in a fixed (home or stationary portable) HF station. AC safety and lightning protection are closely related but let’s defer those topics to the grounding-and-bonding book. Let’s start by getting the definitions straight.
Definition and Myths of Grounding and Bonding
The word “ground” is overused and often misused. Ground can mean a specific thing (a noun), such as a connection to the actual Earth or a common reference voltage. Ground can be a type of thing (an adjective), such as a ground wire or a ground plane. Ground can also be an action (a verb), such as when a capacitor is discharged by a grounded safety interlock. So, we have to be very careful with the word “ground” to be sure we’re all talking about the same thing.
- There are a lot of myths about “ground” and “grounding” that arise from confusing the definitions or frequency ranges or desired effects. Here are four common ground myths:
- The Earth is NOT a sink into which we can pour RF and expect it to disappear. The ground surface and the connection to it have widely varying voltages and impedances at different frequencies.
- “RF ground”—It’s very hard to maintain a “zero volt” difference over a wide frequency range. What might be possible is a small area that has the same voltage over a modest range of frequencies but within fairly narrow limits.
- “Ground loops” can result in hum or buzz, but that is primarily an audio or power-frequency issue, not RF. Any conductive path forming a loop between at least two pieces of equipment is a ground loop and even modest amateur stations usually have many. These can’t be eliminated, so the voltages generated in them must be managed.
- “Single-point ground” refers to an electrically-small point used as a reference voltage or common current return point. At ham-band frequencies, “electrically small” covers from a dozen feet down to centimeters. Trying to tie every piece of RF equipment to one physical point in the station often creates loops with long conductor lengths, causing more problems than it solves.
It’s no wonder that hams are confused!
Bonding is a connection intended to keep two points at the same voltage so that the connected equipment goes up and down in voltage together. Minimizing voltage differences between pieces of equipment (even the ones that don’t have a power connection) accomplishes the following:
- Prevents shock hazards and RF burns caused by voltage differences
- Prevents destructive voltage differences caused by lightning surges and strong RF fields
- Limits current between devices caused by RF voltage differences, this article’s main topic
Bonding sounds complicated and expensive, but it is really very straightforward. To make a grounding and bonding system as complete as possible, you must use the right materials. Learn more in the complete On All Bands article Ham Radio Tech: Grounding and Bonding and RFI.