Mobile Rig - W6RMK (old one)

Finally, I'm getting my mobile rig put together. One of the challenges was figuring out a way to mount antennas without drilling holes in my car (not that I haven't drilled holes before, but it's a challenge to do without). Then, there's the issue of powering the rig, making it re-movable, etc. I'd also like to figure out how to set it up so I can move it to the Landcruiser with minimum hassle. It looks like lots of connectors are going to be involved.

HF Antenna

I looked around at HF antenna options, of which there seems to be three general classes: fixed whips, with tuning coils added/removed by banana jack jumpers, etc.; A straight whip with an automatic antenna tuner (the SGC QMS system being a good, but not the only, example); and various incarnations of "screwdriver" antennas (which have a sliding loading/tuning coil in the middle driven by a modified electric screwdriver). One constraint was that I wanted to be able to move the antenna between the two cars (VW Passat Wagon and Landcruiser), in some fashion.

I haven't operated mobile all that much (except VHF into repeaters, for instance), but somehow, the idea of adjustability without having to stop and get out was appealing. Relays and jumpers would work, but requires fabrication. The ATU with a whip is appealing, but, when I was looking into this stuff a year or so back, it was expensive ($500+ for the SGC SmartTuner); of course, now, SGC has a cheaper box out to do the job. I finally settled on the screwdriver approach, and after looking at the plethora of plans and versions on the web, I took the easy way out and stopped at HRO on the way home one day, and just bought what they had in stock: the NottLtd BBC3. Now to mount it.

The usual scheme with these antennas is something that fits into a trailer hitch receiver, a solution that would work admirably for the Landcruiser, which has a hitch. Some fabrication might be nice to put the antenna in a good place: off to the side and high enough that the coil and whip are above the roofline. Or, when we get a brushguard for the front, we can mount the antenna up there, Aussie style. But, the Passat doesn't have a hitch, and when I crawled underneath, there weren't any likely places for a hitch or for bracketry. The other approach was to make a bracket in the front; no luck there either, no obvious place to bolt it. { but wait, there's more, I DID find a place eventually. see here.}

Finally, I decided to figure out how to mount it to the luggage rack. I had bought a bike rack a while back, so I built a little platform using 1" aluminum square tubing and a 12x24" piece of 1/16" diamond plate. Unfortunately, the diamond plate flexes a bit too much, so I added a piece of OSB (chipboard) under the bottom to stiffen it, and now it's pretty rigid. The tubing is held to the rack cross members with u-bolts (covered in vinyl tubing). The hardware is all vanilla cad or zinc plated, and will probably rust in the next 6 months, especially bolted to all that aluminum, but for now, it works. I picked up a body ground by connecting to one of the rack attachment bolts, under a nice plastic trim cover at the rear.

In the picture at right (clickable for a bigger version), you can see the white PVC cover over the tuning coil, and you can just see the antenna ball at the top of the stainless steel whip. This thing is a lot bigger looking than I expected.. no problems finding it in the parking lot!

whole car thumbnail

Click for bigger (142K) version

Here are some detailed pictures, which are clickable to bring up a page with (much) bigger versions.

General Side View

General Side View

Overhead View

Overhead View

Clamp Detail

Clamp Detail

Some notes:

This is distinctly not carwash friendly! Perhaps, a hinge or some sort of quick release scheme is called for.

Hmm.. seems to have a bad effect on gas mileage. Maybe? More analysis here..

New! I now have the antenna mounted on the front bumper, Aussie style. Not only can you actually see the marks for "optical tuning", but it's a lot easier to jump out and disconnect the whip. The following photo shows the antenna on the right front bumper. I drilled a sutiablel hole in a piece of 2"x1/8" steel, which was then bolted with a sort of clamp to the front tow lug.


DC Power

DC power is always an issue, especially if you're going to run 100W output power. I also have an aversion to directly connecting to the vehicle battery, based on long experience with destroying batteries, unforeseen interactions, etc. And, with new cars having so much electronics, I am concerned about EMI/EMC issues. In the past, my little portable APRS rig used a small 7Ah "gel-cell" charged off the accessory circuit through a diode, but I'm not sure it worked all that well. I did run the battery dead (killing it totally) when the PTT stuck on and the "brick" 2m amp sucked it flat. At least it was isolated from the vehicle supply, so I could still start the car.

This time, I figured I'd put a BIG deep cycle battery in the back and run the radios off that. I haven't figured out how to charge it yet, but, some sort of relay/charger scheme will probably work. Does anyone make a 12V(nominal) input battery charger? I whipped on down to Sears and got a 105 Ah marine battery (non-optimal) and a battery box. The batteries were on sale for $59.99 (+$7 core). I will probably move that one to "home backup" duty, and get a sealed AGM wheelchair battery (Sears had one, at 45 Ah for $75, but no specs available on discharge rates) or similar, because I can just see the crud coming out of the marine battery corroding away the carpet, etc. For now, though, the battery is back there, strapped to the luggage tie down.

NEW (August 2003) - There's a nifty device called an echo-charger, from Northern Arizona Wind and Sun (actually, from the folks who make Heart Interface stuff for RVs and boats) that interconnects two 12V systems appropriately. I've ordered one, so we'll see how it works.

The power is brought to the front of the car via cabling made with 2 (for each side) AWG10 stranded conductors. Eventually, I'll build a little power distribution panel with a quick disconnect. For now, wire nuts are the answer. I also need to figure out how to route the cables.

Linears

After a couple months operating on the way to and from work it looks like a bit of "fire in the wire" might not be a bad idea. Candidates are the MFJ 600W, the SGC cube, the Henry Radio ???

Radio mounting

Still haven't done much with this yet.. It's at the radio on the seat stage. I am leaning towards building a nifty rotating table like WA8LMF built for his (older) Passat. Fairly simple, removable, etc.

I'd like the "radio package" to be easily pulled out for portable operation, etc.

radio/mobile1a.htm - revised 1 Feb 2006 - Jim Lux
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