Importance of Grounding in Amateur Radio

Importance of Grounding in Amateur Radio

Grounding an amateur radio station is important in three ways. First is electrical safety to the operator and the equipment. Second is suppression of stray radio frequency, also known as RF grounding which will improve the performance of the radio in terms of transmission and reception of radio signals. Third aspect is protection from lightning, especially for high rise antennas well above other conducting structures in the neighbourhood. When I started as a ham radio operator in in 1980s, I was mostly concerned about the first aspect as I was not very much aware of the second aspect and thought that the last aspect is beyond my control! I was quite worried about the first aspect because my vacuum tube radio was having a transformer with 600 V AC output. The rectified DC voltage on top of the 807 tubes would be in the range of 845 V.

That was at my parents’ home where we had a grounding system for the home electrical wiring. There was a large grounding pit about two feet from the basement of the building which had been filled with charcoal and salt. A long galvanized iron pipe was driven down into the pit and then connected with thick copper wire to the mains grounding plate. As this was just outside my shack, what I did was to connect the chassis of the vacuum tube radio to this ground system. I would periodically check the chassis with a line tester to enusre that it is not ‘live’! As the dipole antenna coax was connected using a PL 259 connector to an SO 239 connector mounted on the iron chassis of the radio, it would automatically get connected to the ground connection as well.

The ‘lightning protection’ which we used to practice in those days was just to remove the PL 259 connector from the SO 239 to prevent damage to the radio. Of course, that would not prevent lightning from coming inside the shack. Some of my freinds used to install another earth connection with another SO 239 connector to which the PL 259 of the antenna coax would be connected at the onset of a lightning storm, to act somewhat like a ‘lightning arrestor’. One friend who had seen sparking between the inner and outer conductors of the PL 259 which was hanging in the shack during a lightning storm, quickly threw it out of the window to reduce the chance of lightning coming into the shack! But that could have been risky as well, if a major lightning strike occurred exactly at that moment. This same risk is also there when you remove the connector at the onset of a lightning storm.

In my current setup with no high voltage application as I am using commercial solid state VHF and UHF radios only, I am more concerned about RF grounding and lightning protection. Electrical safety is also important as I am using a linear power supply. I test the metal body of the power supply homebrewed and supplied by another ham, using a line tester to make sure that it is not ‘live’. When I installed a CP22E VHF antenna, I used a copper clad iron earth rod which is available in local electrical stores to ground it. It was driven down between the pavement tiles in my garden and connected with a clamp to a 10 sq mm insulated copper wire.

As it is in between my garden pots, it will get automatically moist always when I water the plants, ensuring a good ground conductivity! The other end goes up and was connected to the upper end of the galvanized iron mast on which the CP22E antenna was mounted. I had drilled a hole in the mast and used a clamp to connect the grounding wire. Grounding for the linear power supply comes from the three pin socket of the mains supply which is connected to the grounding system of the home wiring. I do disconnect the PL 259 connector from the SO 239 on the chassis of radio each time I finish my session of operations. This ensures that I do not have to go and disconnect it at the onset of a thunder storm, which I consider risky. I am slightly worried that frequenct disconnection and reconnection could eventually damage the connectors, but I more concerned about the lightning safety as I was told by my one of my Elmers that frequency of lightning strikes have increased over the years due to global warming.

So much for the practical experience, now a bit to the theoretical aspects. While a wire or dipole antenna needs grounding with a grounding rod of at least 8 feet driven into a conducting ground, a vertical antenna needs a metal sheet or radial wires buried in the ground. Grounding for the mobile antenna is connection to the metal chassis of the vehicle. Long back when I had a mobile VHF antenna installed in my first car, I had taken it to the workshop and drilled a hole in the metallic bonnet to get the base of the antenna connected. I needed their help take the coax inside the car and also to fix the bracket for mounting the radio inside the car. I do not have a mobile antenna in my car now, because I do not want to a drill hole in it! Grounding a mobile antenna in a car with fibre glass body could be challenging as well.

Installing lightning arrestors and surge protectors are also important aspects for protection in case of lightning. But these do not give absolute protection as the extent of voltages and currents of a major lightning strike could be way beyond any protection given by these devices. One of my Elmers recently lost a cable television set top box in a lightning strike in spite of having extensive lightning protection measures installed at his home. Some regions are more prone for lightning strikes than other regions as well.

The type of grounding for RF depends on the type of antenna as mentioned. If it is a complete antenna like a dipole or a groundplane which does not need an RF ground, an additional ground is not needed for RF performance. But common mode currents on the feedline has to be avoided using an RF choke or balun. Several turns of coax at the base of the antenna depending on the frequency is a common mode of implementing this. Others use ferrite beads slided on to the coax for the same purpose. A grounding rod is not enough as RF ground for a quarter wave vertical antenna and needs additional radials buried in the ground. Number of radials needed will be more if the vertical antenna is shorter than quarter wavelength. If it is half wavelength, grounding rod may be enough as an RF ground.