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
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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