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RUBBER DUCK ANTENNAS


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Author Unknown
 
RACES BULLETINS 023-025, 1986

Rubber duck antennas on hand-held radios are a severe compromise on efficiency. On the plus side is their short size and flexible forgiveness to brutish handling. On the negative side is their terrible radiation inefficiency, probably worse than many of you expected.

When did you last replace your helical spring antenna we call the rubber duck? On testing a hundred or so portable radios that had been out on the fire lines for a few weeks we found a typical 60 percent failure rate. Most of the antennas looked fine. The only way you can detect an invisible rubber duck failure is by measuring the microvolts per meter with a calibrated receiver over a measured range under controlled conditions, such as done routinely by the Boise Interagency Fire Center. Since this is difficult for most to do, it might not be a bad idea to replace rubber ducks as a matter or course when they show signs of wear or if they are a year old. You might want to consider using a telescopic antenna under non-violent conditions to vastly improve the range of your hand-held.

The National Bureau of Standards ran some tests that proved what we had long suspected. The efficiency of a hand-held is dependent upon how much antenna it has and how good the ground plane. Most portables have very poor ground planes; the more metal the better. Also the more antenna the better. Hence the rubber duck is a woeful but often necessary compromise. But if a portable is not going to be subjected to the abuse of fireground or street cop utility, you should consider the telescopic quarter-wave antenna if range is important. Compare the figures and discussion that follows.

Be aware that the telescopic antenna is nowhere as rugged as the rubber duck but it will talk circles around it. You might say that the quarter wave whip is to the rubber duck what a 106 inch CB quarter wave whip is to a 36 inch whip on a base loaded coil to compromise range for low garages. Our reference antenna in the Public Safety high band and 2-meter Amateur radio measurements below is a quarter-wave telescopic antenna, extended, and held at face level: One-quarter wavelength extended and at face level = 0 dB One-quarter wavelength collapsed and worn at belt level = -40dB Rubber duck held at face level = -5dB Rubber duck worn at belt level = -20dB Translated, this means that a 5-watt hand-held with a rubber duck worn on the belt has an effective radiated power not of 5 watts but only .05 watt. Held at face level the radio has an ERP of 1.6 watt. 15dB is quite a difference!

In the material above we gave you facts and figures of the quarter-wave telescopic versus the rubber duck for Public Safety VHF Highband and 2-Meter Amateur handhelds. The 40 dB down for the nested telescopic relates to those commercial models where the telescopic disappears within the radio. Such an antenna won't break when it's nested but it won't receive worth a whoop either. In those radios where the collapsed quarter wave is external to the radio they break very easily. For that reason we recommend the style that has a spring at the base. The spring makes it very forgiving of elbows and other bum raps. We have not researched or measured five-eighth wave antennas because they are too long for most public safety use and because they typically require too many telescopic sections. The more sections the more chance of troubles. Few people take the time to correctly telescope any hand-held antenna. They should never be whacked down with the palm of the hand on top and push. They should be pulled down with the thumb and first two fingers.

If you are interested in the figures for 450 MHz, using the table above, they are respectively 0dB, 30dB, 5dB, and 30dB. One more reference for the technically inclined-the loss of a telescopic antenna compared to half-wave dipole: VHF -5dBd and UHF -20 dBd. Telescopic antennas should be changed at least annually and whenever they become the slightest bit loose. Any looseness can mean a poor RF connection inside the antenna where you can't see it or fix it. Simply change it.


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 Most recent revision 03/20/08