Mobile Rig - W6RMK

I've got a new car, a BMW 325 convertible (well, I've had it for about 9 months now) and am finally getting the mobile rig into it. The old mobile rig was in a Passat and I talk abou that here. After thrashing around trying to figure out how to shoehorn the old radio into the new car and have it look half way decent AND keep the passenger seat available, I decided to get a new radio, which simplifies things a lot.


I have the Icom IC-7000, which has a separatable faceplate, so the radio goes in the trunk (near where the CD-changer would normally go) and the faceplate goes in the front, in front of the sunglasses drawer. The cable runs from the trunk, through the hatch for the subwoofer/skis, under the back seat, along the front console, etc.

There are some issues with the audio path, since the radio has the speaker, which puts it in the trunk. I've done it two ways: hook up an external speaker to the jack on the faceplate; and feed the audio into a aftermarket adapter widget that makes it look like a CD-changer to the radio. (I suppose I could get the MP3 player mod for the radio, and just run a little cable from radio faceplate to MP3 player jack). There is a pretty significant RFI issue with the CD-changer AUX input scheme, though.

HF Antenna

While the radio always presents a bit of a packaging challenge, for HF mobile, it's the antenna that is hardest. On a convertible, you don't have a roof to work with, either as a ground plane, or as a place to put a luggage rack to which you can clamp an antenna.

In the Passat, I used a screwdriver antenna, which worked ok, but was very slow and tedious for band changes (or even frequency changes on 40). It also, absolutely, positively has to be in sight of the operator, which means in front. If there weren't a whole lot of places to mount it on the Passat, there's even fewer on the BMW. Also, I wanted to start fooling with ALE, which requires rapid retuning. So, it looks like an autotuner is the way to go.

In the past few years, the price on these has dropped. There are three major players in the autotuner business: SGC, LDG, and MFJ. SGC is the only one that is really catering to the mobile, end fed antenna market. I have a couple of LDG desktop tuners, and I'm happy with them, but the appeal of putting the tuner right at the feedpoint (the SGC paradigm) is very attractive, especially with a physically short antenna.

So here's the current installation sitting in the parking lot at work. The antenna on the left(drivers) side of the car is the stock FM antenna, then the HF antenna with the SGC tuner, and on the right side trunk lip, there's a 3 band Comet VHF/UHF.

A closer view of the antenna end of the car with the HF antenna tuner in a plastic box.

The power to the tuner is carried by a standard 4 conductor trailer connector (the waterproof rubber thing with 3 males and 1 female on one side, and the mate on the other). Power comes from the 4 pin tuner connector on the IC-7000. Currently, just the +12V is fed to the tuner, and nothing is done with the TUNE output from the radio, nor the TUNE input on the tuner.

The actual HF antenna is a 10m whip, with a 25 foot (or about that) wire wrapped around it.

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.

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.

radio/mobile.htm - revised 11 Sep 2008 - Jim Lux
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