Friday, May 25, 2012

mobile nerdness

I put up a post on g+ about getting some ham radio antennae on muh car and thought I would post some pictures in case anyone was interested.

The basic idea was to make something I could easily deploy and take down, so there wasn't a whole lot of hole drilling and a lot of stuff is in temporary locations.  Pictures and a talk-through after the jump.

Which should be coming up right about........ now.

The Plan

I have a Yaesu FT-857D transceiver.  It's got 2 coax antenna connectors on the back:  one for HF and one for 144/444 MHz.  W9DAN sent me a Newtronics Hustler changeable antenna (with whips for 10, 15, 20, 40, and 75 m) along with an old school fender mount.  I also managed to purchase a 1/4 wavelength 2m antenna from KCOMM before they closed up shop.

I wanted to build a cross bar for the luggage rack in order to house the 2m antenna as well as provide a flat surface for anything I happened to be hauling.  In the interests of keeping the height of the truck as low as possible, I decided to mount the HF Hustler antenna on a trailer hitch.  Although I didn't end up drilling too many holes in my car, I did do a fair amount of drilling into metal bits attached to the car... I feel I should get partial credit for the "real ham" requirement.

The Power Problem

Anyone who's tried to mount a radio in their car knows that the one, unalienable rule that you must always follow is:  "drill a hole in your firewall and hook the rig up directly to the battery".  Running the power off of fuse boxes or cigarette lighters is inviting trouble in terms of electrical fires, RFI, or unexpected power losses if the voltage falls too low.

So I ended up hooking my power leads up to a fuse box:

Basically, the transceiver's power is from the two wires at the top (both fuse protected) using an extra power cable I snagged from KCOMM.

Ok, it's not exactly a fuse box.  On the driver's side of the Chevy Trailblazer under the rear seat is a power panel that already has a direct line to the battery.  This panel is used to manage stuff like the remote door locks and OnStar (which is under the passenger side rear seat and I have completely unplugged, btw).  Installing this cable was a matter of putting on the 10 AWG ring connectors on the power cable, disconnecting the negative terminal at the battery, checking that there was no power with the voltmeter, checking a second time, then a third time to satisfy my OCD, and finally screwing those puppies down.  I had to clip the ring connector for the positive terminal in order to get it to fit over the threaded post in the panel.

From this location, the power cable can reach pretty much anywhere in the truck if you don't mind it being exposed.  Routing under carpeting and around seats will probably be tough.  It easily allows the transceiver to sit up in the front passenger's seat for the time being.

The Trailer Hitch Hustler Mount

To make the trailer hitch mount, I first disassembled the Hustler bumper mount to remove the actual antenna mount (looks kind of like a trailer hitch ball) from it's mounting plate.  The next step was to drill 3 holes through a 2" Interlock trailer hitch (around $25 from Lowes) and attach the Hustler mount to the hitch with 3 stainless steel screws.  In order to drill the holes, I used a normal drill bit, clamped the old Hustler mounting plate down over the trailer hitch, and just kept pressing down until I punched through.

The next picture shows the wiring on the bottom side of it:

The topmost screw is being used for a grounding strap that attaches to the car.  The big center screw is for the positive line on the coax (basically, the thin center wire) and the bottom is for the negative (the sheathing).  As you can see, I used more ring connectors (10 AWG is probably overkill, but ya use what ya got).

The other end of the coax got a PL-259 connector with an RG-58 adapter.

Finally, here's a picture of the hitch in place with the mast and whip attached for 40m:

Some notes about this setup:

1) Can't open the hatchback with the antenna on (dammit)
2) The hitch is loosely seat, so there is a lot of bouncing and swaying while the car is moving
3) The ground plane in this configuration absolutely sucks... it would be better served mounted on the crossbar, but height becomes an issue then.

I got the car up to 60MPH with the antenna on the hitch, but was pretty nervous about it.  I'm probably going to chicken out and only use it when the truck is stationary.

2m on a cross bar

For the 2m antenna, I decided to build a cross bar similar to the one for a light bar described here.  I basically just used a 1"x1" square steel tube about 4' long (I think it cut down to around 43 or 44") and used a 1" wide x 3/8" thick piece of steel for the feet that went into the runners.  I cut all the steel with a sawall using an 18T metal blade, and then drilled some holes for 10-24 flat head screws into what was roughly the center of them.  The flat head was important in order to get clearance over the bolts that hold the luggage to the roof of the car.

I then JB welded the 10-24 screws into the feet, and then inserted them into the rails so I could measure exactly where to drill the holes in the square tube.  The screws were near enough to the end of the tube that I was able to tighten them down a bit with a narrow wrench.  The final step was to drill 3 holes onto the back of the tube in order to attach the antenna's mount plate:

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