Part 14
Welcome to Part 14 of our series.
Last time we started looking at vertical antennas. This month we're going to continue in that vein, with an emphasis on antennas for hand-held radios (commonly called HTs, or Handie-Talkies). Just about every ham owns one or more. Most often they are either single band for 2 Meters, or dual-band with 70 CM added. And they're quite convenient, allowing us to walk around the house or easily move into the car or office and keep in touch. There are a few drawbacks, however. First, most HTs put out at best a 5 Watt signal. That's plenty if you're close to the repeater or other stations you want to work. But as the distance grows, our signal becomes harder for others to copy. Second, those cute little antennas are terribly inefficient. It's a simple matter of physics and a trade-off in order to have something small, light, and portable. And third, we then compound the problem by operating inside of a car or a building where our signal gets blocked by the metal car body, aluminum house siding, or other things. Take a look at these three diagrams:
Rubber Duck External Antenna Better External Antenna
The pictures represent our signal as seen by a repeater antenna (with a perfect omni-directional pattern) located at the center. At left, "Rubber Duck" is our baseline -- an HT with a standard factory antenna. In the green zone, we're Dead Full Quieting, or clear and perfect audio into the repeater. As we move further away and into the yellow zone, we're likely to get reports like "a little scratchy but copyable". Get into the red zone and we hear "you're in and out", "I know you're there but I can't get more than a few syllables" or similar. And of course, move into the black area and you have no signal into the repeater at all.
The next picture shows the improvement when we add a basic external antenna. In a car, that's typically a 1/4 wave whip with either a magnetic mount, or something more solidly attached. Finally, the picture on the right shows further improvement from adding a better (as opposed to the 1/4 wave whip) antenna. Put away those measuring tapes and rulers -- the size of the circles simply indicates that by far the biggest improvement will come from adding an external antenna. A better antenna will offer a marginal signal increase, but at the expense of higher cost, more height, and probably the need for a better mount. Then again, if our favorite repeater is within that margin, it may well be worth the investment.
The same holds true at home or at work. You can often attach a magnetic mount to an air conditioner outside the window, or some sort of metal bracket. Even if you can't get it outdoors, you'll get some improvement by putting it on a refrigerator, filing cabinet, or similar -- even a cookie sheet!
I'm often asked if it's worth replacing the stock factory antenna with a better one. Well, a six-inch antenna is going to radiate like a six-inch antenna, more or less. There's no magic, and there's no getting around those pesky laws of physics. One antenna might be slightly better than another, but all in all there's not going to be much difference. A longer antenna will work better, certainly. And if that's what you need to get from the red zone into the yellow or green, go for it.
Another quick fix for the rubber duck is to add a counterpoise. Rubber duck antennas depend on your (lossy) hand and arm to make up the "missing half" of the dipole. Attaching a 1/4 wave, or odd multiple, of wire to the outer shell of the connector will improve things. For a 2-Meter/70 Centimeter radio, about 19 inches does the trick.
Just keep in mind that an external antenna will make the biggest difference.
One final point -- attaching heavy coax cable to your HT with a simple adapter can put a lot of stress on that little SMA or BNC connector on the radio. A much better solution is a short jumper made of thin flexible cable like RG-316 to act as a strain relief.
That's it for this month. Next time we'll talk some more about vertical antennas.
73 for now
John Bee, N1GNV
Quicksilver Radio Products
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