Going Mobile (In Someone Else's Car) Part 2

Mirage BD-35, dual-band HT amp, $179.95The problem: You more RF power than a handie-talkie provides in a package that can be easily/quickly moved from one car to another when you have a mobile ARES/RACES assignment.

You are in a non-ham’s vehicle and can’t do anything dramatic, like running power direct from the vehicle battery. Here is the first of two ways to solve this problem, one uses your talkie and the other a mobile rig.

Solution 1: Keep your talkie, buy an amplifier and magnetic mount antenna. Package the amp, handie-talkie, and whatever power option you choose so that you can easily carry them with you.

There is a lot to recommend this approach. If you have an extra HT, this is a good use for it, assembled with the amp and antenna as a Go-Kit. Or you can use the radio you normally carry and store the amp and antenna separately, until needed.

You can purchase an amp, single or dual-band, for between $100 and $200. Make sure you buy an amplifier that’s designed for HT input power. That way you can get 30-50 watts with only a few watts in. You will also probably want a speaker/mic so the radio can sit on the seat or be in a bag with the amp while you talk.

Challenges:

• Choosing the amp
• Powering the amp and talkie
• Selecting a magnetic mount antenna
• Packaging the station

Choosing an Amplifier

The Mirage B-34 is a 2w-in/35w-out 2-meter FM-only amplifier that sells for $99.95. A similar model that includes SSB support and a receiver pre-amp, the B-34G, is $119.95. The BD-35 (shown), a dual-band amp, puts out 45w on 2-meters and 35w on 70cm and costs $179.95. (Mirage is owned by MFJ.)

All these amps are reasonably rugged and designed for mobile use with a talkie. They do get quite warm on extended/frequent transmissions, which may limit how you package them.

Power Issues

The real challenge here is the power supply, which will come off the cigarette lighter outlet. You could just attach a plug to the end of the amp’s power cord, run the talkie off its own battery and be done with it. Of course, you could also blow a fuse in the vehicle and maybe burn up the amp, or even the vehicle. That’s why we fuse at least the postive side as close to the battery as possible.

Powerwerx Red-Dee-2 PowerPole spiltterGiven the choice, I would rather purchase an Anderson PowerPole distribution block and use it to provide 12 volts to both the radio and the amp. You could use a Powerwerx Red-Dee-2 spiltter (shown), which is available online as well as at Ham Radio Outlet stores.

I say “you” could purchase the Powerwerx splitter, but I wouldn’t. First, there is no fuse. Second, there is still no fuse. Third, I don’t like how the cables attach on both ends. And did I mention there is no fuse or reverse polarity protection?

Saratoga PowerPanel 4I prefer the Saratoga Amateur Radio Products PowerPanel for applications where I need something small to distribute power to multiple PowerPole connectors. The device is fused and provides reverse polarity protection.

For this purpose, I’d use a male cigarette lighter plug wired to a PowerPole connector to feed the PowerPanel. The panel will support any device with 15-45 amp PowerPoles attached, which in this case would be the amplifier and a DC power cord for the talkie.

Do better than I’ve done and tape a spare fuse to the PowerPanel, which I will add to my personal to-do list.

The PowerPanel is a neat solution for powering most anything, though for permanent installations and/or larger installations I purchase a distribution panel with individual fuses for each connector. And, yes, I do have fuses at my desk.

The BD-35 amp pulls 7 amps of DC power, so the cigarette lighter ought to be able to supply enough power.

The Antenna

The first thing to know about a magnetic mount antenna and someone else’s car is how to avoid scratches. This is done by NEVER sliding the mag mount onto or off the car. To attach, just set the mount where it needs to be (ideally the center of the roof). To remove, TILT the magnet to one side and lift—never slide the magnetic mount (and all the little pieces of metal it has collected) across the vehicle.

Some people put something between the car and the magnet, like cloth or plastic wrap. I’ve never done that, however, so I can’t say whether it works or not.

I would use a full-size mag mount for this application and have available, perhaps, two antennas to attach to it. One would be something short—like a quarterwave for a single band or a short dual-bander. If I can get one with a spring or some other way to avoid unfortunate interactions with overhanging obstructions (like trees), so much the better.

The second antenna would be something larger and a little gainy, just in case the amplifier doesn’t quite do the job by itself.

Comet SMA-to-SO239 adapterMost modern handie-talkies are equipped with God-awful SMA connectors. These tiny things make the radios look neat, but aren’t a very good choice mechanically. You will probably need an adapter to connect the antenna to the radio and for this I recommend an SMA-to-SO239 adapter that has a connector attached to each end of a short length of very thin coax, which acts as a strain relief for the SMA connector on the radio. Comet makes these and I think I paid $15.00 for mine.

Do not connect large coax directly to a radio-mounted adapter, OK?

Packaging the Station

If you were to just load the amp, radio, and power panel into the vehicle, you might then run the coax from the antenna into the car though a rear window (makes it easer to exit the front door). Attach the coax to the amp, and the amp to the talkie. Next, push the amp under the seat and run the power cord to the cigarette ligher jack.

Set the talkie on the seat next to you and use a speaker/mic to listen/talk and you are ready to go. Perhaps, you can even bring a small earphone with you so the radio will seem quiet to anyone else in the car.

I generally think a Pelican case is overdoing things, in price if not protection. A small fabric briefcase can easily carry all this gear—except the long antenna—and unless the amp gets hot you can simply leave it in the case. The radio might stay in the case as well, with just the mic, coax, and power cord visible outside. Wrapping the amp in a length of bubblewrap when you’re not using it is also a good idea.

Be use to add a case for the radio, or promise yourself to always keep it from bouncing around with the amp and its nasty heatsink fins. Don’t need additional radio scratches if they can be avoided. (The bubblewrap can solve this problem.)

The most important thing, however, is having all this gear assembled in one package—ideally in the trunk of your car—so it will be ready when you need it.

In a future post, I’ll talk about the option—which may be less expensive—to carry a mobile rig from car-to-car.