The OZARK PATROL

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The picture on the left, from the 4 State website, shows the method of bending the component leads. I chose to make the leads longer to avoid any damage from the soldering iron, especially to the transistors.

This is a capacitor added to tune the antenna. It doesn't come with the kit. To couple the antenna to the radio, a very low value capacitor is used. It's made by twisting two pieces of wire together and is called a "gimmick." A gimmick capacitor has a value of about 1 picofarad per inch, depending on how tightly the wire is twisted. I wanted to be able to vary the capacitance.

The capacitor used was 0 to 28 pF, which is too high. I could only mesh the plates a tiny amount and then it was too much. I put a 4.7 picofarad capacitor in series with the variable. What do you suppose that did to the value of the variable capacitor?

To calculate the value of two capacitors in series, the formula is C1 x C2 / C1 + C2.   So (28 times 4.7) divided by (28 plus 4.7) = 131.6 divided by 32.7 (I used a calculator) = 4.02. The variable capacitor is now 0 to 4 pF! It is perfect for this. You don't really need it if you're building the kit; the gimmick will work fine. I just happened to have the variable capacitor available, so I used it.

Gimmick capacitors. You'll put your eye out with those things!

Value of a typical gimmick capacitor.

The audio output of the radio is disappointing. The volume is so low It was actually in competition with the noise from our refrigerator while listening to it. Then I plugged in a pair of headphones and the difference was amazing. The speaker was replaced. It improved the sound, but not the volume. Once you listen to the radio with headphones you probably won't use the speaker. The volume in the headphones is so loud that you'll have the sound turned almost all the way down.

The speaker frame is very close to the terminals on the regen control, so be careful when attaching it.

In another effort to get more volume, I replaced the 2N3019 transistors with some 2SC458s that I had left over from the Astro Commander walkie-talkies (seen elsewhere on this site). I don't think it made a difference. The level of sound from the speaker was still abysmal, and It wrecked the cool look of those silver and brass metal 2N3019s. The reason I used the 2SC458s was because they worked so well in the walkie talkies. I knew they were good to at least 27 megahertz (way more than what was needed here) and the walkie talkies have plenty of volume. The "Pittsburg style" construction lets you swap out a transistor in less than a minute. This came in handy when comparing the performance, since listening conditions on the short wave bands can change from minute to minute.

The 4 State QRP Group considers the "Ocean Hopper" an ancestor of the Ozark Patrol. The Ocean Hopper DIDN'T HAVE A SPEAKER. Perhaps instead of trying to improve the dismal volume of the speaker in the Ozark Patrol, just ignore the fact that it even has one.

If the Ozark Patrol was made without a speaker, it would be cheaper, and nobody would get the impression the radio doesn't work very well, because it DOES work very well if you use headphones. A cool "4 State QRP Group" decal could be placed where the speaker used to be.

...and then I had an idea.

While watching some YouTube videos of other Ozark Patrols, I got an idea. Yes, another one. That's a total of FIVE, no, THREE ideas! The videos show an external amplified speaker plugged into the headphone jack. So why not make the amplifier on-board? Literally on the board.

For a buck you can get this amplifier kit from China on ebay. No postage! I ordered three. I mean, five. The soldering pads are very small, so there is a learning curve after flowing all that solder onto the Ozark Patrol.

The little amplifier is mounted behind the volume control. "Set it and forget it."

THREE WAYS TO CONNECT THE AMPLIFIER

To install the amplifier you first disconnect the speaker. The input to the amplifier are the wires that formerly went to the speaker. The leads from the amplifier output then go to the speaker. Power comes from the on / off switch on the front panel. Set the volume on the amp to where you want it, then forget it. You still control the volume from the front panel, but now you have some SERIOUS volume.

You can pick up a ground for the amplifier from any of the screws that mount the speaker. You can also use the B- from the battery. The 9V+ comes from the On/Off switch.

Partial schematic with LM386 amplifier

Connecting the input of the the amplifier directly to the transformer (in place of the speaker) gives the radio a tremendous increase in volume. It can be ear splitting. There is a 10 mfd capacitor on the LM386 module across pins 1 and 8 that controls the gain. You can remove it if you use this configuration..

By bypassing the last transistor and the transformer, the sound is clearer and the range of the volume control is better, though it isn't nearly as loud. This is very easy to do, all you need is a wire from the collector of transistor Q2 to the amplifier.

Here's the wire attached to the collector Q2, which goes to the input of the amplifier.

NOTE: Connecting the amplifier this way will NOT cut off the speaker when the headphones are plugged in.              To turn off the speaker, turn down the volume all the way on the little amplifier.

A third way to connect the amplifier is to take the output from the collector of Q3. If you use this configuration, remove the 10 mfd gain control capacitor from the LM386 module.

Here's the wire attached to the collector Q3, going to the input of the amplifier.

Which way works better? They each have their advantages. Click on the picture to see a video of some tests.

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