Hello everybody and welcome back to my blog. Today we are going to wrap up on series on Antennas by talking about antenna safety. How can an antenna be harmful that this would require a post by itself? Well, there are a few things that we are going to cover today, one of which is a rule set-fourth by the FCC a few years ago and we will talk about general safety and maybe even touch on station safety as well.
So lets talk about the rule that was set fourth by the FCC. It was originally issued by the FCC back in 1996…ok so it was a little long than a few years ago. Times flies and all that. Anyway, what the rule states is that the power radiated from your antenna cant be above a certain threshold that could could cause thermal damage to a human being, especially those areas like the eyes and for us men, the testes because of their relatively low blood flow.
That being said, this is an excerpt from the FCC FAQ page…
ARE RF EMISSIONS FROM AMATEUR RADIO STATIONS HARMFUL?
There are hundreds of thousands of amateur radio operators (“hams”) worldwide. Amateur radio operators in the United States are licensed by the FCC. The Amateur Radio Service provides its members with the opportunity to communicate with persons all over the world and to provide valuable public service functions, such as making communications services available during disasters and emergencies. Like all FCC licensees, amateur radio operators are required to comply with the FCC’s guidelines for safe human exposure to RF fields. Under the FCC’s rules, amateur operators can transmit with power levels of up to 1500 watts. However, most operators use considerably less power than this maximum. Studies by the FCC and others have shown that most amateur radio transmitters would not normally expose persons to RF levels in excess of safety limits. This is primarily due to the relatively low operating powers used by most amateurs, the intermittent transmission characteristics typically used and the relative inaccessibility of most amateur antennas. As long as appropriate distances are maintained from amateur antennas, exposure of nearby persons should be well below safety limits.
There is a lot to this rule and I don’t wants to go into great detail of it because this post would be huge, but I’m going to summarize it. Basically this ruling states that the radiate energy that your antenna puts off has to be below a set level that you determine by a few different math equations. There are equations for both controlled and uncontrolled exposure limits. Controlled is defined as someone who knows the antenna is there and what its doing. Uncontrolled is basically the general public. For example, a person walking behind your vehicle in a parking lot while you are transmitting. They don’t know that you are transmitting and may not even notice that you have an antenna on your vehicle, therefore they don’t know that they are being exposed to RF radiation. To make sure that your station is below this level, a study has do be done annually if you meet certain requirements, like power output level, height of your antenna, etc. If you would like to read more about this, which I think everyone should at least have an idea what its all about, the FCC has put out a bulletin on it named OET Bulletins #65. One of the topics you will find in at that link is the a complete pdf of the bulletin and a few supplements to it. Starting on page 16 of the main bulletin is where it talks about amateur radio in particular.
OK, now that the official rules are out of the way, let’s talk about other safety information regarding your antenna and station setup. First off, lets talk about electrical safety. All the equipment in your station should be on one master switch and everyone in your household should know where that switch is located. All your equipment should have a good ground. All wires carrying power should be of the proper size for the current being drawn and should be insulated for the voltage level involved. Bare wires, open chassis connections and exposed connections are just an invitation for accidents. Always remember that high voltage-low current sources are just as dangerous and low voltage-high current sources. The average household 120V power source is probably the most dangerous instances of getting hurt because it is often overlooked because it is a part of everyday life.
Always remember to kill the power and unplug equipment before doing any work on them. If you are doing work inside the equipment, it is also a good idea to bleed off any capacitors or tubes, don’t rely 100% on the bleed-off resistor.
Station and antenna grounds is probably the second most talked about topics in ham radio, second to antennas. With grounding there are three different types of grounding involved in your station, not all of the them are required in every station setup though.
The first is the safety ground. The safety ground is there to protect you from shock if one of the mains or high voltage power wires somehow get disconnected and comes in contact with your chassis. This is most commonly supplied by the ground pin of you house plugs. They should be connected to ground according to the National Electric Code(NEC), and your rig’s chassis should be connected to the safety ground.
The second is the Lightning ground. There are many different methods of grounding your antenna and station to try and help protect it from a lightning strike. You can buy a commercial lightning arrestor and hook your coax to it and it to a ground rod. Some people say that you can put a loop or a loose knot in your coax before you bring it inside. The theory behind this is that electricity travels in a straight line and wont come around the curve of the coax. How true this is and if it really works, I don’t know, but the way I see it, if it is possible that it is going to save a $1000+ radio, why not do it. It wont affect your transmissions or your line loss and it will also provide a drip point for moisture to drip off your coax before entering you house. So if it doesn’t work to stop lightning at least it will provide a place to loose moisture. For more information about lightning protection, check out the ARRL’s Lightning protection page
The last type of grounding is the RF ground. A RF ground is only required for certain types of antennas; ones that require current flow to ground to complete the antenna circuit. An example of this is a quarter wave verticle. One wire of the feed line is connected to the base of the antenna and the other is connected to ground. One thing that you have to remember though is that the connection to ground has to be low RF resistance, otherwise you will be loosing a lot of power to the ground. One way to provide this low RF resistance is to place multiple radials buried slightly underground. The smaller the antenna, the most radials you will need. Once you get up to half wave length, a ground rod will be enough and you wont need the radials. If you use an antenna such as a ground plane or a dipole you don’t need an RF ground, as long as you keep common mode current off your feedline. A current or choke balun is most commonly used for this.
Let’s move on to some general safety tips. Ham shack safety has a lot of aspects to it. If you have little kids, they might want to come in and play with mommy or daddy’s things. They don’t know what can hurt them. Even non-ham friends that come over can touch something that can hurt them because they might not know any difference. Shortly after I became a ham, I saw an article somewhere about how this person had a light setup outside the room where his station was. If he was inside working on a piece of equipment or doing something that could hurt him or someone else that came in, he would turn that light on. That way his family and/friends knew not to come in.
- A fire extinguisher is a good thing to keep in your ham shack. Just make sure that if it is an electrical fire that break out, kill the power before you spray it with the extinguisher, this is where the main power switch comes into play.
- Whenever you work on a piece of equipment it is a good idea to have a static free mat and a ground connection to you before you touch the insides or anything. Especially with the equipment that we have now-a-days, the tiniest electrical discharge can kill a chip in a radio and cost a lot to fix.
- Try to keep any fluids away from your radios or computers. Liquid and electricity don’t mix to well. At the very least, drink from a “spill-proof” cup.
- If any wires from your station can be seen from the outside, try to put them in bundles and zip tie them together. Guys, not only does this look better to your wife, but if you are like me and move your legs alot when you are sitting at your desk, it will keep you from getting your feet tangled up and unplugging something or even ripping the ends off a connector.
- Mount your antenna as high as possible. Most people will already do this because the higher the antenna the better the coverage you have right? Well, another reason to do this is because of that FCC Rule that we talked about earlier. The farther from an antenna the less RF radiation that you/your neighbor/your friends will receive.
- Mounting your antennas high though adds another point of safety. If you mount your antennas high, you have to have something to mount them on be it a tower or push up pole. The higher you go the more support it requires as well. So, some things that you could do is put a fence around the base of your tower to keep anyone who doesn’t belong on your tower off of it.
- If you tower or pole has an guide wires on it, you might put some red ribbon or spray paint them a little above ground level, say from two to six feet from the ground. Doing this, of course, is no guarantee that no one will run into them, but at least it might help.
I think that about wraps up this subject for now. One thing I will leave you with, SAFETY FIRST! I want to thank you for reading my blog and I hope that you have enjoyed my posts. If you did and/or are liking what you read, please share my posts with your friends and like my facebook page for post updates. The link to my facebook page can be found on the top right of my page, just click on the facebook icon.
73 de Curtis, K5CLM
- Antennas – Part 1
- Antennas – Omnidirectional – Part 2
- Antennas – Directional – Part 3
- Antenna Tuners
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