Tips on Mobile Ham Radio Installations

     I often get asked about mobile ham radio installations, so I thought I would post some tips on that subject.
     First and foremost, good grounding is of prime importance, especially doors and hoods.  In every vehicle I have owned, I took a piece of 1/2" ground braid and put crimped ring-tongue solderless terminals on each end then fastened it between every door and the frame.  I did the same to the hood and frame.  Remember to do the same to the car's trunk, too.  This practice ensures that each component of the vehicle has the same ground potential.  Even tho the doors and hoods are connected by hinges, you have to remember that those hinges have grease on them and grease is an insulator when it comes to electrical current and ground paths.
     The exhaust pipe can act like a giant antenna, too, causing QRM.  It is not connected to the frame of the vehicle solidly because it needs to "float" by means of some special brackets that have a piece of thick rubber in between.  So, I take a piece of ground braid and connect it between one of the muffler clamps and a bolt on the frame.  If there is no bolt nearby, find a thru hole in the frame and stick a bolt thru it.  Or, you could drill and tap a 1/4-20 hole in the frame and fasten the braid to that bolt.  Make sure you use a lockwasher on that bolt to keep it from vibrating loose.  If there is any undercoating on the frame, scrape a little of it off before inserting the bolt, then once it is tight, spray some touch-up undercoating on the bolt.
     The DC power line should be ran directly from the battery thru the firewall to a screw terminal strip inside the vehicle.  Make sure the terminal strip has enough terminals to acomodate all of the stuff you will be hooking to it.  I use #10 stranded wire for the battery run and it is the red/black DC wire that is standard for automotive work.  At the battery end, solder in an in-line fuse holder and fuse it with a 25 amp fuse.  Also, at that same end, put a big snap choke there with as many turns of wire as you can get on it.  Put another snap choke on the other end of the DC cable.  This will help attenuate alternator whine and fuel pump noise.  Snap chokes can be purchased from www.allelectronics.com fairly cheap.
     Lets talk a bit about antenna installations.  With dual band 2M/70cm antennas, I always try to use a mag mount and I put it right in the middle of the roof.  This gives the antenna a good ground plane for the signal to reflect off of.  The signal will be strongest in whatever direction the vehicle is facing, front or back.  If you have a regular car, you can use a trunk lip mount for the antenna and that will work OK, too.  Routing the coax from a roof mounted antenna, I just run the coax to a rear door and shut the door on the coax somewhere near the top.  I don't usually have any problems with water leaking in when it rains.  Routing the coax from a trunk lip mount can be tricky because you have to snake it under the back seat and up front to the radio.
     What is the next thing you need to do now that you have the radio and antenna installed?  Check the SWR! For this you will need a good quality SWR/Power meter.  You will need to set the radio on a simplex frequency such as 146.520 and check the SWR there.  A reading of 1.3 or lower is acceptable.  Now set the radio to the 70cm band and put the frequency at 449.00.  Why 449?  Because most 440 repeaters have a 5 khz split between the receive and transmit frequencies.  In other words, if you are on a repeater that is on 444.100, your rig will transmit on 449.100.  This is where you need to check your SWR.  Most dual band antennas don't have SWR readings that are equal on both bands.  Sometimes you have to play with the adjustable whip on the antenna to strike a happy medium.  I try to get them as close as possible to each other.  There have  been times when I have had to trim a bit of material off the bottom of the whip with a bench grinder, but you have to be VERY CAREFUL about this.  If you trim even a few thousandths of an inch too much, it can change the SWR dramatically.  Don't do this unless there is no alternative.  Another option is to raise or lower the position of the whip in its socket then tighten down the setscrew.
     Now lets talk a little bit about HF antennas.  I have used Ham Stick antennas and Hustler antennas but the drawback of those is that in order to change bands, you have to change antennas, which can be a big pain in the butt.  I thank God for the invention of the screwdriver antenna!  The one I use on my truck is the Little Tarheel II which will transmit on 80 thru 6 meters.  Again, the key to getting an antenna to work well is a GOOD GROUND.  On my truck, I took a piece of 1/8" aluminum and bolted it between the tool box and the truck bed with about half the material sticking out beyond the truck bed.  The antenna is mounted thru a hole in the material.  I then ran a piece of copper wire from that plate to the frame of the truck for the ground connection.  This arrangement works well.  It is out of the way and yet high enough for the antenna to use the roof as a ground plane.  I use an Ameritron screwdriver antenna controller for tuning but it can  be a pain in the butt because if the antenna loses its position, the preset position numbers on the controller will be off, too.  That is why I have ordered an autotuner for the antenna.  I have not installed it yet and I do not remember the name of it, but as soon as I get it installed and working, I will add a product review to this blog.
     The radio I use in the truck is the Yaesu FT-857D because it has HF, VHF and UHF all in one box.  Believe me, I use all of its capabilities, too.  I have had it since 2007 and it has been a very good performer.  When I am on HF, a lot of guys can't believe I am mobile because they don't hear any noise from the truck!  I guess the noise cancelling ability of the stock mic works quite well.  There are times when I wish I had an amplifier in the truck for HF, but then I would need a heavier duty screwdriver antenna to handle the extra power....maybe someday.