Mobile ham radio on a tight budget? Yep, It can be done with some creativity. There's a plethora of cheap Chinese handheld radios out there. These cheap new radios have in turn brought down prices on quality used ham gear. Another thing that's adding fuel to this cheap equipment fire is that commercial and public safety entities are moving towards narrow band radios. The old "wide band" radios have heavily depreciated meaning super cheap prices on the used market. The majority of ham radio repeaters on the air are wide band so all this retired gear is perfectly usable for our purpose providing it works in ham radio frequencies.
This instructable will show you how to add a Chinese voltage regulator board to any handheld radio, allowing you to run it off 12v in the car. This does away with worrying about batteries so you can mount the thing somewhere instead of having it bouncing around on the seat.
Why do this? I can think of three good reasons..
1) You want a ham radio in the car but have an ultra tight budget
2) You want a ham radio in your beater vehicle that isn't worth stealing
3) You want something tiny and easily concealed without spending a ton of money on a micro sized ham radio.
I came up with this idea while looking for a ham radio for my beater truck. The doors on it don't lock so I wanted something that looked as un-interesting to a thief as the truck itself. The solution revolves around a commonly available DC voltage regulator board that can be found on ebay or amazon.
SKILLS AND TOOLS REQUIRED..
You must be able to solder, have basic handtools, and a multimeter. There is some ham radio terminology used in this instructable so a ham radio background is helpful.
Step 1: The Regulator Board
The board I used to turn the car's 12v into something the handheld radio can deal with is a Chinese DC voltage regulator board. The one in the picture is fairly common and can be bought for about $5 shipped. It can source up to 3A and can accept up to 40v yet have variable output down to about 3v. There's an adjustment on it and a display that shows you input and output voltage. There is a switch on the board to toggle between in and out voltage.
It's fairly straight forward, voltage in, voltage out, a switch to toggle display, a small potentiometer you turn with a jewelers flat head screwdriver to adjust output.
Step 2: Radio Selection
What radio to use? This instructable is about using a handheld radio as a mobile (car mounted) ham radio. There's hundreds of choices out there between new and used. At time of writing, a new Baofeng UV5R dual band radio can be had for under $30 shipped. While these radios are an outstanding value, they have one very big shortcoming... the receiver.
The receiver on the Baofeng and Pofung radios for example is extremely sensitive but has little selectivity. It's easily overloaded by strong nearby transmitters on other frequencies. This problem is not unique to Chinese radios. Lower end ham radios also suffer from this. This could cause problems for you in urban areas that are saturated with radio signals. One workaround is to always use PL decode if the repeater sends tone. This helps quite a bit.
Another radio option that promises excellent performance but comes with its own hurdles is a used commercial radio. Narrow banding of commercial frequencies has caused the value of used gear to plummet. Radios that were once in the thousands can be had for the price of a new Baofeng. The catch? Programming frequencies into them. First you need to make sure the radio you're getting can be programmed into the VHF or UHF ham bands. This part is fairly easy, just look up the model number on the web. The actual programming part is were things can get annoying.
Commercial radios typically require a special cable and software to program. The software can range from free (ultra rare) to costing $100 or more. Then you need a programming cable and possibly some form of interface box. There are shops that have this stuff but they don't work for free.
Wanting something with a decent receiver I opted for a retired commercial radio. Not wanting to have to polish anyone's ego for a programming favor, I opted for a commercial radio that can be programmed via CHIRP (free!) software via the standard ($7) Baofeng programming cable.
CHIRP is the best kept secret in radio land. It's open source, free, radio programming software. It doesn't program everything but does cover quite a few Kenwood commercial radios. The radio I went with, the Kenwwood TK260 (pictured) can be found for as little as $10 ea in lots, has a good receiver, uses Baofeng hand mics, and is CHIRP programmable.
Step 3: Where You Will Be Connecting the Regulator
On the back of all handheld radios, you will find battery contacts (pic 1). This is how power gets from the battery, into the radio. You will be soldering wires here. I bet your saying which is which?
Most radios have just two connections. Look at them closely, sometimes they are marked and the positive will be marked +. In the event yours aren't marked and you got a battery with your radio, take a look at the battery and see if the contacts that mate with the radio are marked. Having a battery for your radio with some semblance of a charge makes this much easier as all you have to do is check the battery contacts with a meter to figure which is + and which is -.
If nothing is marked you can either try to do some research and hope for a schematic or you can roll the dice and hope the radio was built to common modern practice. Common practice is to make the metal case of the radio the ground point. This isn't 100% true for all manufactures but so far all the modern (relatively speaking) radios I have seen are built this way. In pics 2 and 3 I'm pointing to the battery contacts on the back of the radio. Notice one is bolted directly to the metal frame of the radio? That one is - and the contact surrounded by plastic is the +.
Some radios use a pair of spring loaded pins. You can figure out which is ground by using a multimeter and touching one lead to the nut on the antenna connector and another to the pin in question. With the radio off, the - pin will give you a dead short on a resistance check.
What if your radio has 3 pins? Some do. Look for markings, no markings? Check the battery for markings. No markings on the battery? See if the battery only uses 2 of the 3 contacts. This will help you narrow down your detective work.
Step 4: Wiring Up and Mounting the Board
These boards fit well into the battery compartment of most handheld radios. You will be soldering a short length of wire directly to each of the battery terminals of the radio. You need to work fast here. Clean the terminals with a light sanding so the solder quickly takes. The - terminal on my radio is metal to metal but the + terminal is on plastic. There's no margin for dilly dallying. Solder quick or risk melting something!
Once soldered in, route the wire, place board where it will go, trim wire to a comfortable working length, strip wire, tin ends, connect wires to OUTPUT terminals on board (watch polarity), and get ready to glue board in place. My preferred cheap and quick method for mounting these boards is to use RTV silicone rubber.
Make sure none of your radio terminals will short against the board when its set down in place. If there's a chance of that, a small piece of electric tape over the offending terminal is all you need. Put a thick bead of silicone RTV on the bottom side of the board and stick it in place. Use a rubber band to hold it in place. Allow 24hrs to dry.
Step 5: Power Up and Adjust
Once the RTV silicone has dried, you are ready to power up and adjust.
Turn radio off if it has an actual mechanical click switch. Feed 12v to INPUT terminals of board from a suitable 12v power supply. Remember input terminals are marked for polarity. When board is first fed power it will light up and display input voltage (pic 1).
On the board you will find a small pushbutton and a tiny potentiometer. The pushbutton toggles between input and output voltage. The potentiometer (pic 2) adjust the output voltage via a small screw that requires a jewelers flat head screwdriver.
I have seen handheld radios that run on 3.7, 7.2, 8.4, 9.6, and 12v. Obviously if your radio runs on 12v you don't need this board and hopefully you caught that before starting this project. For all the others, adjust the output voltage to match that of the battery used on the radio (pic 3).
Step 6: All Done
All ready to get wired in! 12v power from the car will be fed to the INPUT terminal on the board. Watch polarity!
Being that this is a handheld radio and consumes such little power, it can even run off a cigarette lighter adapter. For a more permanent install find an accessory tap on the fuse panel that can provide at least 5A. No need to run cables all the way out to the battery for this one. Don't forget to fuse any connections you make to your vehicles wiring. Add an external antenna and a handmic and you have a full fledged mobile setup for a fraction of the price.
What range to expect? Being you will likely be limited to a max of around 5w, antenna gain is everything. A 5/8 wave or better antenna is a must with such low power. Don't let the low power discourage you though. I typically get into repeaters 20 miles away using 5w and a good antenna on my old truck. 5w can go far on an efficient antenna.
You will need an adapter to go from your radio's antenna connector to the PL259 commonly found on ham radio mobile antennas. These adapters can be had for a couple of dollars on ebay.
Enjoy your setup!