Saturday, November 16, 2013
With the weather not so nice this morning, and with 15 centimeters of fresh snow on the ground and in the air, I decided that I would spend time in front of my computer going over some of the projects that I have on the go, and share some of my thoughts with you on the subject of antennas.Lately I have spent a lot of time playing ham radio, as I have built a new HF antenna system for my mobile, and from the start of this project that goes back about 3 months, to the present with a working antenna system as part of my mobile, it has and continues to be a very pleasurable time for me, as I now run tests on this new antenna system.
You know how much that I enjoy going down the road with my mobile, exploring roads less travelled, and spinning the dial of my HF radio, while listening for radio signals on far horizons. As enjoyable as that is for me, part of the enjoyment of this, is trying out new antennas that I design and build in my shop, then mounting these newly minted antennas on my mobile, and once I have the kinks worked out, there is nothing more satisfying than making contact with other hams spread across the world on one of my own antenna creations.
Today, ham's do not have to build radio gear as in years past, when you actually had to build your own receiver and transmitter, as well as your antenna system before you could get on the air. As time went by, and more and more manufactured ham radio gear became available, hams got away from building their own receivers and transmitters. The result of this is that hams have left gear building behind, and today it is the norm for most hams to visit there local ham radio outlet, where they can choose from a vast selection of wonderful ham gear, and once the selection is made, they can be on the air in short order.
If there is one place that hams can still get much enjoyment out of building what their using, is antennas. Its a given that all transceivers need a antenna, and it does not matter whether it be your favorite 2 meter rig, or your state of the art HF rig, they all need a antenna to receive and talk on. This is one area of ham radio that you will find it very pleasurable to roll your own. I have been a ham for more than 20 years, and in that time I have always built my own antennas, whether they be for my ham shack, or for my mobile. It has nothing to do with saving money, but has everything to do with taking pride in what you built with your own hands. There is nothing that brings a thrill, like making contact with hams on the antennas you build and put on the air.
Don't forget that a big part of your complete antenna system, is the care that you put in to the installation of both the antennas and the radio gear. In my case, its all about going mobile, and I consider myself well versed in all things related to mobile ham radio. I run a 12 volt shop in my daily work, and I cringe at some of the installations that I see. I don't necessarily mean ham radio installs, but all types of 12 volt installs. Still, this post is about mobile ham radio, and I will make my comments in relation to mobile ham radio.
It all begins with the installation of your ham gear, and the first thing you want to do is have a plan. Don't just start installing the various components, without first putting some thought into where everything is going to be mounted in and on your mobile. It does not matter with where you start, but I normally like to install my antennas first, and once the antennas are installed, you can then think about mounting your radios.
Of course, it goes without saying that the antenna that resides on your mobile is only half of a successfully designed antenna system. In my case, my mobile has a body that sits on a frame that required bonding to eliminate noise and increase the ground-plane beneath my HF antenna. This in turn increased the performance of my overall antenna system. This also took a fair amount of time, and to accomplish this, I used 1” wide tinned copper flat braided ground straps with eyelets at either end, used to bond the various components of my mobile together.
It is important that you use flat braided strapping and not round wire for bonding, as RF travels on the surface rather than through the wire, therefore flat braid has more current carrying capacity due to its larger flat surface. One of the problems that I initially experienced, was engine noise on the receiver of my HF radio. The engine of my mobile had a existing ground strap that was at the most a ¼” in width, and was not capable of eliminating the ignition noise that I was experiencing. I added a additional 1” inch wide strap from the engine to the frame, I also grounded the exhaust system near the engine to the frame and again at the rear of the exhaust system to the frame, resulting in a much quieter receiver of my HF rig.
With any decent mobile install, bonding is everything, and it is the RF ground under the antenna that will make or break how well your mobile performs, especially on HF. It is important that you keep all of the ground straps as short as possible, and do take care when drilling holes in the body, so that you do not drill in-to any existing electrical harnesses that may not be visible. I used quality stainless steel fasteners along with stainless steel serrated washers for attaching the ground straps throughout my mobile.
So, don’t forget that your antenna is only one half of a dipole, and in the case of a mobile HF antenna, the missing half is the vehicle and its capacitance to the ground under the vehicle. The single biggest factor with respect to efficiency for any mobile and especially on 80 meters is ground loss, so maximizing this half of the antenna system is essential, and this is accomplished through bonding.
The installation of the radio equipment along with the associated cables, wiring, and antennas takes some planning before beginning the actual install, but upon completion, you are rewarded with a system that is not only a joy to look at, but to operate as well. So with that, I will cut this short, and continue working on my new antenna design. I hope that I have given you food for thought, and I will be listening for you on the bands when I am travelling down roads less travelled.
Talk to you soon...73...VE6AB
A link for more of mobile ham radio by VE6AB