|Editor’s Note: Storm Copper has an eclectic staff with many and varied interests as well as specialty fields of expertise. When a customer’s question arises concerning Ham Radios, we call upon our own Tracy Carter who not only operates a Ham Shack; he repairs his own equipment as well.|
By Tracy Carter
Storm Copper is one of the leading manufacturers of copper grounding components and solutions in the U.S., so we receive many calls and emails each week asking about grounding electronics in the home as well as large and small businesses. One of the most common questions we receive is related to Ham Radios and their prerequisite antennas that protrude skyward in much the same manner as a lightning rod.
Unfortunately, for many, the reason for the call is their antenna has already done an effective impression of a lightning rod. Lacking a proper grounding system at the time of the incident, customers often find themselves in the salvage and recovery mode and are looking for information on the proper way to prevent a second experience surrounded by the smell of burned circuit boards.
While there is no way to totally protect electronics from a direct strike, the good news is that a megawatt strike is a fairly rare occurrence. The goal of careful hams should be to think maximize and minimize. A good grounding system will maximize your gear’s protection and minimize your exposure and resultant risk.
One important thing to remember is to forget an old saw from “supposed experts” who often disparage newcomers to the hobby by telling them “That’s just overkill”. In my opinion you can never overkill a grounding system.
Here are the steps to properly grounding your Ham station:
1.You will first need a ground bar near your equipment that is large enough to handle the brunt of a surge. “I will say not IF it happens but WHEN it happens.” Always run individual ground wire(s) or braid(s) from each piece of equipment (radio, amp, power supply etc.) to the ground bar, never daisy chain a ground. Your coaxial cable has already introduced enough inductive reactance into the puzzle we sure don’t need more!
2.Next, let’s talk about RF (radio-frequency) Grounding a bit. An important element of a total grounding profile requires proper RF grounding. A recent question from a fellow ham radio operator who was setting up a radio station on the second floor of his home, raised a subject that can be confusing. He was looking at our ham radio grounding kit as well as 4 gauge solid copper wire. He stated 28.900 MHz would be the highest frequency he would be using normally and stated the quarter wave length was approximately 17 feet. He maintained that shortest length that he could get would be approximately 30 feet, and was looking for suggestions.
His miscalculation was not unusual. He was referring to RF grounding on 10 meters, mid-band frequency of 29.000 MHz the quarter wave would be 8.06 feet. For RF he only needed to calculate the feed wire, not both legs. So that will cut the total length to 17′, or basically in half.
The rule of thumb is to use quarter wave length of the highest HF frequency used to plain an RF ground system. The formula to calculate quarter wave is (234/MHz = feet of wire). So, if you are going to operate on 10 meters let’s say center band at 29.000 MHz, the formula gives us 8.06 feet. Most normal Ham Shacks can never achieve this unless your shack is in a basement. By the time you take away the 4 feet of flex-braid or wire that goes from your amp to the ground bar you now only have 4 feet to get to the outside and attach to the ground rod. This rule of thumb formula is for total electrical length from ground rod point of attachment to the chassis of equipment being grounded.
It’s not the end of the world if you do not have a perfect RF ground solution, I don’t have one either! As radio operators we are adapting a room in your home to a radio station and not designing a facility that is ideal so you will have to settle for the best you can make it. Here’s an example of how hard it is to be perfect. Even at 7 MHz, the distance is only 33.42 feet, which is still hard to achieve if your shack is not at ground level or if it’s in the center of your house. Some is better than none at all!
Sorry please don’t shoot the messenger, that is just the way RF and our magnetic field of the earth works. A quarter wave length is the rule of thumb on where to place the first ground rod for good RF protection. So given your shortest length is approximately 30′ you can only protect against RF at a frequency of about 8.00 MHz. This would give you RF protection on 40 – 160 meters.
There are lots of Hams that never use an RF ground rod. It’s usually OK until you add an amp or the conditions get just right and the microphone finally nails your lip when you’re trying to get that unique DX station. I’ve also heard of Hams not even grounding their rigs. The first close lightning strike takes their entire station out, and at that point grounding becomes a step they “should have taken.”
Also make sure the wire going to the first ground rod called the (RF ground rod) is of adequate size, a minimum of #4 AWG Solid is the standard. You can use stranded in heavier gauge but never use anything smaller, you don’t want this to turn into shrapnel in the event of a direct lightning strike. This would be a good time to point out the seriousness of this subject. As mentioned earlier, nothing will stop a direct lightning strike! If this happens while you’re sitting at the radio you’ll be toast and more than likely all equipment in your station.
Bonding is a critical element and unfortunately the most overlooked aspect of a good ground system. Many feel the ground rod they just put in for RF is adequate for total system grounding, but consider this situation.
Let’s say lightning strikes a tree close by, within 100 yards, halfway between the RF ground rod and your service entrance ground rod. The energy wave is so intense at that close of a distance it will split into two separate transformer windings, your house ground and all associated wiring and your RF ground and all associated coaxial cables and chassis. Here’s the kicker, you now have two different voltage sources tied to your Ham equipment. Can you think of what happens next? Arcing, popping and possibly open flames will follow, but hopefully you only “let the smoke” out!
All grounds RF, Electrical Service Entrance and Tower Grounds need to be bonded or tied together! I believe taking this additional step is the root of the saying “That’s a little overkill” I mentioned earlier. I truly think cost is the real reason behind that saying and hope no one is sitting at their radio when lightning decides to drop by for a visit. The price of a life is far more precious than a little copper grounding wire!
73′s from KA4JPB