Installing a Ball Mount for Mobile SSB
First, be sure you have the right sized hole-saw to match the hole in the base of the ball mount, and the right size drill bit to match the three or four holes in the ball mount. Next, be sure you have the correct size bolts and nuts to mount the ball mount. Now comes the first change from the ordinary. When you buy your mounting bolts, however many they are, buy some flat star washers, combination inside and outside star washers with the biggest teeth you can get. Get two for each bolt/nut pair plus several more, in case of loosing one and for use later on. These washers are called by several different names and shake-proof is just one name. With so many different types of washers on the market now, it isn’t hard to get confused, but if you ask for inside/outside star washers, some one will be able to get what you need.
Next, you will need a socket to match the nut on the inside of the ball mount and the ratchet wrench to match. Be sure to have the allen wrench to match the allen set screw on the ball mount so that in conjunction with the socket for the nut in the ball mount you will be able to line up your mobile antenna vertically. Take the metal backing plate and the rubber gasket and put them back in the box that the mount was packed in. As a point of interest, if you can afford it buy a stainless steel mount it will last longer. Now take the ball mount and place it on the spot on the car that you have picked to mount the antenna. Look at the diagram of the ball mount mounting.
Place the mount so two of the mounting bolt holes are facing to the front of the car, truck, or whatever the antenna is going on. Be sure that the two bolts will be vertical. This will allow the strain of any impact to be spread more equally between the backing plate and the car body. Mark the mounting holes and the large hole for the base of the mount with a pencil. Check inside the fender or wherever the mount is going to see if there is any danger of drilling a hole in some undesirable object like the gas tank, and that you will have clearance to work in as things progress.
After you have determined that the path is clear, center punch each location that has to be drilled, and commence to drill the bolt holes and the center hole for the mount. After drilling the holes, be sure to clean off all of the chips from the drilling, and de-burr all of the sharp edges from all of the holes. If you leave any chips on your car they will rust and that will be a toe hold for the rust to attack the car body.
Failing to de-burr the sharp edges from the holes can result in unneeded bloodshed as you slice your fingers and hands up as you install the ball mount and antenna matching network. Don’t forget the matching network! Every little bit helps. Now put the ball mount with its gasket up to the vehicle body and put the bolts through the mounting holes, then on the inside of the body, put a star washer over each bolt, and put the backing plate over each star washer. Put the other star washers on each bolt with a nut on each bolt. Tighten all but one of them down firmly so the star washers cut into the backing plate and through the inside coating on the vehicle body into the metal.
This will give you multiple airtight grounding contacts to the car body, which will lower the rf resistance of the ground. This is better than the usual set screw that goes through the backing plate you are supposed to tighten up until it goes into the metal of the vehicle. Now screw the antenna into the ball mount and loosen the big nut on the inside of the mount and the allen set screw on the outside of the mount. Adjust the antenna until it is vertical then tighten the ball mount nut and the allen set screw back up enough so that the antenna will not flop around as you drive around and hit branches, etc.
Assuming you already have your coax run from the rig position to the trunk area, with plenty left to work with, the next thing that you do is to strip the coax and solder a lug on the braid. The coax center conductor needs to have whatever is needed to connect it to your matching network. Soldering the center connector to the matching network is best. The lug you put on the braid needs to fit under/around the mounting bolts for the mount.
Now take the one nut that you did not tighten very tight off and put the mounting bracket for your matching network on the bolt, put another star washer on top of the bracket so that you have a star washer under as well as on top of the bracket. Mounting the matching network is going to be up to you but it is a good idea to have one common ground for the coax, matching network, and car body, which is why you should try to have the matching network bracket using one of the ball mount mounting bolts.
Next, put the coax ground lug on top of the star washer which is on top of the bracket. Then, put another star washer on top of the coax lug. Next to last thing is put the nut on top of the whole thing and tighten it down. The last thing is hook the center conductor of the coax to the matching network. This should finish the mechanical installation, just be SURE that you have a good ground at the rig end of the coax for both rf and dc.
As a point of interest, a good source of heavy gage dc cable for the rig or to go to a spare battery, is a good jumper cable. Just cut off the clamps, run the cable and put battery connectors on the appropriate ends. Another source of heavy gage cables is the welding supply business. Welding cable is very flexible and easier to handle, so you might keep this in mind for your mobile and other high current applications.
At this point it might be a good idea to go back and check all bolts for tightness and generally look over the installation. If all looks ok, all that you have to do next is to put the rig in the car, get the swr bridge and head out for somewhere, like a mall parking lot, where there is nothing that will interfere with you tuning up the antenna. You need a place where there is nothing within a quarter wavelength of your antenna, and a half wave is even better. Also, this includes anything above the antenna as well. You must tune up in the clear because when you do get into the clear, all of the tuning will change, causing you to resort to chants and other spiritual sayings.
Now, for the last comments. There are those who will question the use of so many star washers, but the purpose is to make a good connection and keep it. The sharp edges on the star washers will cut through any oxide and dirt and anything else that might be on the metal surfaces. By cutting into the metal, the edges of the star washers, being embedded into the metal, make air-tight multiple connections between the metal components of the mount and coax lug, mobile bracket and the car body. The multiple ground connections lower the rf resistance between the vehicle body and the ball mount backing plate. The rf ground resistance must be kept as low as possible to eliminate losses, as the transmitter will put power into a load, regardless if it is the antenna or a combination of antenna and bad rf ground.
All that matters to the transmitter is that it sees a 50-ohm load and that is all that matters. So, if your transmitter is putting the power into a combination of 30-ohm antenna impedance and 20-ohm rf ground resistance and you are running 100 watts, 40 per cent of your power is being lost in the ground connection. Not too swift! You need to keep this in mind when you do any kind of installation, either at a fixed location or a mobile installation of any sort, the lower the total rf resistance of a circuit the more power will go into the antenna. That is where it counts
Originally posted on the AntennaX Online Magazine by Richard Morrow, K5CNF
Last Updated : 12th March 2024