Heil Sound

The HM-10 microphone is at the center of Heii Sound s Concept 2000. Unlike other amateur radio microphones, the HM-10 uses professional cannon-type 3-pin connectors. You can buy the HM-10 by itself, or with the Heil HC-4 ■DX Dream Machine*' or the Heil HC-5 full range element.

Interface the HM-10 to your transmitter Input connector by specifying the cable with the right color: red. Kenwood; yellow, Yae^ su- blue, ICOM; and black, special. Operate pit or vox, handheld or desk mounted. Adjustable booms and goose-neck mounts available.

The HM-10. built for durability, is heavy and rugged. Wired, with plugs, carrying case, stand adapter, colored cable, and foam

windscreen, the price is $80. Heil Sound, PO Box 26; Marissa IL 62257 (618) 295-3000. Contact: Bob Heil. Or circle Reader Service Number 205.

If INC.

Hustler announces a new HF mobile mast for their line of mobile resonators and accessories. Model MO-4, a 22* all-stainless steel mast, creates many mounting op-ttons previously unavailable to the mobile HF operator. It's ideally suited for RVs, trucks, vans, and cars with pEastic bumpers. You can mount it on trunk lips, mirrors, roof racks, and ladders. In conjunction with standard Hustler resonators, you can install the MO-4 on a high quality magnetic mount.

You can make a shortened dipole with two M04 masts and a matching pair of resonators. You can assemble a tri-band dipole. good for apartments and areas of restricted space, by adding two Hustler VP-1 triband adapters and two resonators.

The MO-4 comes with three 30" tip rods for 10, 15, and 20 meter resonators, No tip rods are necessary on 40, 75T or 80 meters Suggested retail price, $20. Hustler. Inc., One Newtromcs Place, Mineral Wells TX 76067, (817) 325-1386L Or circle Reader Service Number 209

MFJ ENTERPRISES, INC.

Dave Ingram K4TWJ shows you how to collect, restore, and operate classic ham gear in his book, Golden Classics of Yesteryear, published by MFJ Enterprises, Inc. Remember the 6L6 rigsP Heathkit DX-100, Collins KWM-1, WRL Globe Scout, HaHicrafters, RME, Hammulard, National HROs, Eimac tubes, Vibroplex, Speed-X, Dow KEY, McElroy. . ?

The book es packed with real-life tales and easy-to-build weekend projects from the 20s, 30s. and 50s. K4TWJ shows you how to build a "Tailender"—an earfy DX memory keyerthat requires no power supply or electronic parts, but works "like a champ." He includes fa or

vorite circuits, telegraph keys and bugs, and other ham topics.

Dave has authored over 300 articles and 12 books He writes the "World of ideas" column in CQ Order his iatest book for $10 from MFJ Enterprises. Inc., PO Box 494w Mississippi State MS 39762. Telephone: (601) 3235869 or (800) 647-1800. FAX: (601) 323-8551. Telex: 53 4590 MFJ STKVi Or circle Reader Service Number 210.

Photo C. Large capacitor IF filter for the 110 volt supply.

Battery Charging Methods

Photo A The complete charger. Note the 0-500 mA panel for current adjust

Photo C. Large capacitor IF filter for the 110 volt supply.

Battery Charging Methods

You can charge batteries by several means. Two of the most popular are voiiage limiting and current limiting. Current limiting, as the name implies, limits the current going nnto the battery. The voltage Is aHowed to move about, but within limits. As the battery becomes charged, the current drops and the voltage comes to rest at the full charge voltage of the battery.

In voltage limiting, the vottage is preset at the fuH charge setting, and the current is allowed to move about If a realfy discharged battery is connected to a constant vohage charger, heavy current will flow into the battery and possibly damage it.

As with alt battery chargers ano the batteries being charged, the manufacturer has the final say as to how much current and at what voltage the battery will be considered ""charged/" I've been using Yuasa sealed lead-acid batteries for portable use. They are rated at

20 hours at 60 mA to 10.5 volts (1.2 amp/hour), Great for running HW-8s in the woods. Yuasa recommends, for cycle use, a charge voltage of 14.4 to 15 volts, with the current at 250 mA.

Universal Battery Charger

So, enter the universal battery charger. It's nothing special; in fact, you've probably seen some of the circuitry before. Most of it is tried and true, sure-to-work stuff. Now( that's what we both tike to hear, right?

A lot of battery chargers use the LM317 to control the charge voltage. Since I'm not one lo re-invent the wheel, I'm going to use it, too. The LM317 comes in many case styles. Radio Shack sells the LM317 in the popular TO-220 case. If you have one in the TO-3 case, so much the better. The TO-3 case seems to dissipate heat better A trimmer in the adjust lead of the LM317 sets the output voltage Notice there are two different tnmmers. f added a switch to select between two

Mike Bryce WB8VGE 2225 Mayflower NW Massillon OH 44646

Portable Operation

Operating portable requires very little—one portable radio and a source of power to operate it from. IVe always been inclined to operate portable with solar panels, but sometimes they're just too much trouble to set up. Likewise tor conventional 110 volt power supplies. Ruins all the fun if you have to dig up a hundred-foot extension cord. Operating portable from the deck of the house just isn't the same as doing the same in a field or in the woods.

Because of the small current drain of most QRP rigs, battery power is quite attractive, A small Gel/CelP will operate my Argonaut for many a weekend, But

Low Power Operation what do you do when that battery needs charging? I just connect it up to the solar panels and let the home-brew control circuit do its thing. What's this? You don't have solar panels for battery recharging? Well, that's what we're going to build this month: a 110 volt battery charger, but with a twist—actually, a pulse or two. This unit will charge all kinds of batteries, from Gel/Cells to sealed lead-acid batteries, vented lead-acid batteries, and good "oi NiCds.

I've tried to do something a bit different this month. With a few exceptions, you can get all the parts from the local Radio Shack store I buift my version from both the junk box and Radio Shack, But before we get too carried away, let's look at how this critter works.

Photo A The complete charger. Note the 0-500 mA panel for current adjust

Photo B. Inside view of the charger Most pans mount on the periboard, Photo D, Heat sink on LM317. Bridge rectifier is glued to the back panel 72 73 Amateur Radio • August, 1989

difieren! set pomts, one for 12 volt charging and the other for 6 volt charging Now for the added goodies thai make this charger a bit different.

Notice that a 2N2222 transistor's collector is connected to the common of the selector switch. When the transistor is off* the regulator operates normally. When the transistor is on, lit pufls the ADJ line to ground, through the 22ÜQ resistor. This turns the LM3i7off, Now you're asking, "What turns the transflor on?" Good question. Simple answer. A 555 timer chip, that1 s what. The "ol come-to-the-rescue 555 is wired for stable operation. With the components shown, we can adjust the duty cy-cte of the 555. The more OFF the transistor is, ihe more current will flow into the battery via the LM317r Less duty cycle, less current.

Advantages of Pulse Charging

In other words, we charge the battery by using high current pulses, rather than a constant current. Those 7 2 vol! RC batteries are charged just like this. That's why you can recharge one 7 2 vol" battery from a car battery in Jess than 15 minutes Charge currents can approach seven amps or more, but the duty cycle is low enough to avord damage to the cells.

By using pulse charging, we can charge the battery without overheating it The parts passing the current to the battery will also operate cooler. All and aJI, it's a slick way of charging a battery.

Let's took a bit closer. The timing components adjust the duty cycle of the 555-1 ve panel-mounted the adjustable control so that I can adjust the current to suit different capacity batteries, with the same voltage The output of the 555 is a square wave The more on, the higher the duty cycle. You can look at the output with a scope or a VOM. However, you'll only see a voltage move about (as you adjust the duty control) on the VOM due to the meter averagi ng out the result. The scope will reveal a square wave Not the best looking waves you've ever seen, but square waves nonetheless, which will turn on the transistor switch.

Time to heat up the soldering iron!

Construction Details

As noted earlier, you can buy most of the parts at Radio Shack. The meter t used in my charger, which has a range of 0-500 mA, came from my junk box, I found it the most useful when setting the charge rare for the batteries.

Volts Battery Charger Circuit Diagram
Schematic for the universal battery charger.

Most of the circuit is like a circuit for a conventional power supply. T1 supplies 18 volts AC at 2 amps, A bridge rectifier, rated at 4 amps, supplies DC to the filter capacitor 1 used a smalt glob of epoxy to mount the bridge rectifier to the back case panel. The filter capacitor, a computer grade unit, smooths out the DC. Don't worry too much if you can't get the same amount of capacitance I used jusi try to get it as large as possible.

A 7812 regulator supplies 12 volts to the 555 timer, since the direct output of the filter capacitor is a bit high for the timer.

The LM317 requires a heat sink. I use a small screw-on unit, if you wish, use the inside back case to heat-sink the regulator. If you do, be sure to insulate the device from the metal chassis.

I mounted the parts, including the trimmer pots, on a Radio Shack copper-plated perfboard. A socket for the 555 makes troubleshooting easier. In point-to-point wiring, keep the heavy current leads short and direct. Attach wire to the battery with five-way binding posts. If you follow the schematic, you'll have no troubte building the charger

Check over your wiring, especially the 110 volt wiring, for er* rors. You might want to divide the charger into smaller modules for building and testing. Good idea. Start with the 110 volt side. You should see about 20 volts on the filter capacitor.

With the 555 timer out of its socket, turn on the supply and check for 12 volts on the output of the 7812, While the 555 is still out of the socket, switch the voltage selector switch to either 6 or 12 volts. Adjust the proper trimmer to the finish charge voltage. Switch to the second trimmer and adjust it atso. Again. I set mine for 7.2 volts for 6 volt batteries and 14.4

volts for 12 volt batteries.

Turn off the unit and install the 555 timer into the socket. With a battery connected to the output, and the voltage switch set for the proper voltage, adjusting the duty control should make the current meter go up and down. Of course, if the battery is fully charged to begin with, you won't see much current flowing, Because of the blocking diode in series with the output, you cari leavti -ihe bstrery connected to the charger and not worry about the battery discharging if the charger is turned off-

That's about all there is to it.

One final point. This unit is only for charging batteries. DON'T try running anything from it. You'll get all kinds of strange results.

With a few changes, you can have a really versatile unit. By using an LM350, output currents of 5 amps are possible, if you build the charger as I did. you can charge up to 1.5 amps. I don't recommend this charger to charge large lead-acid batteries. 105 amp hours or more.

Next time you get the urge to operate out in the field, you won't have to worry about dead batteries! fH

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