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Author Topic: Best Rubber Duck Antenna For 2M?  (Read 2740 times)
RADIOHEAD
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« on: August 15, 2004, 09:55:24 PM »

I'm looking for a rubber duck antenna for 2m work. I need one with the highest gain possible.

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KG4RUL
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« Reply #1 on: August 16, 2004, 07:17:45 AM »

In general, longer is better. Also, use a counterpoise to maximize radiation.
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K0BG
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« Reply #2 on: August 16, 2004, 10:04:21 AM »

Rubbie duckies don't have gain, they have loss. In fact, some aren't much better than a leaky dummy load. There are dozens of companies making replacement antennas for handhelds which telescope out to near 1/4 wave lengths and work much better. Of course, they also break easily.

For best results, buy a good 5/8 antenna, and properly mount it.

Alan, KØBG
www.k0bg.com
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KE4SKY
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« Reply #3 on: August 16, 2004, 04:14:02 PM »

The National Institute of Science and Technology tested Public Safety "high-band" VHF antennas. Most  flexible antennas commonly used on portable business band, EMS, fire and marine transceivers have -5db, “negative gain” compared to a quarter wave whip held at face level.  Amateur 2-meter antennas would give very similar performance.  This means that a 5-watt portable VHF with flexible antenna has an effective radiated power of only 1-watt.  Placing the portable on your belt produces -20dB of attenuation, reducing EIRP to about 50 milliwatts! UHF results are no better...  

Flexible "rubber ducky" antennas are rubber covered helical springs, intended to withstand rough handling, but they are not indestructible.  Flexible antennas used on wildfire lines for several weeks showed a 60% failure rate.  Flexible antennas should be replaced as soon as they show ANY apparent kinks, cracks, abrasion or other wear to visual inspection.

An expedient to improve a flexible antenna is a counterpoise wire (19.5" long for 2-meters, 11” for 222 MHz or 6.5" for the 70 cm band) of stranded wire, crimped and soldered to a battery clip, which you attach to the shield of a BNC connector, or use a ring terminal to fit over an SMA connector, enabling you to thread the antenna over it.  Reinforce the soldered connection with heat shrink to resist flex.  A counterpoise prevents transmitted RF from coupling with your body. Your antenna now performs like a center-fed dipole, instead of an "end-fed dummy load!"  The main lobe of the radiation pattern can be "aimed" by, grasping and pointing the end in the direction where you need a stronger signal.

Some after-market and home-made antennas perform much better than the standard helical "rubber duck." A J-pole antenna constructed of 300-ohm twin-lead rolls up easily and fits into your pocket. When thrown up in a tree, it increases both height and gain.  Full-sized, flexible 1/4 wave and telescoping half-wave antennas work very well.

A quarter-wave provides unity gain when used with a counterpoise and held at face level.   This represents a 5 dB improvement over a short flexible antenna, because most of the effective signal is radiated. If operating from a vehicle, connect your portable to a magnetic mount mobile antenna to provide a clear RF path outside the vehicle.  This overcomes substantial attenuation, -10dB or more which results from operating a portable unit from inside a metal vehicle.  Always carry suitable adapters so that you can connect your portable transceiver to an outside base or mobile antenna, when one is readily available.

In marginal operating locations a telescoping, half-wave is much better, because it provides the same unity gain without a ground plane that a 1/4 wave antenna does when used with a ground plane.  A half-wave antenna can be pulled up into a tree, dangled out a window, attached to a window pane with suction cups, or be used bicycle or motorcycle mobile, or in city driving on a window clip mount.  A telescoping half-wave increases useable simplex range of a typical 5 watt, 2-meter portable from about a mile in average terrain with the stock flexible antenna to 3 miles or more, depending upon terrain, ground clutter, foliage, and any vehicle or building attenuation.  Adding a counterpoise to a unity gain antenna enables a portable unit to keep in reliable contact within 5 miles of an incident base equipped with an elevated, gain antenna, 20-30 ft. above ground.

Telescoping antennas are more fragile and work best when stationary or in the open, avoiding side impacts or rough handling.  Avoid prolonged mobile use of telescoping antennas on window clip mounts at highway speed, because excessive flexing loosens their internal electrical connections.  Never collapse a telescoping antenna by whacking it down with the palm of your hand. Gently pull it down with your fingers.  If you note any wobbling or looseness in the sections, replace the antenna.

Flexible antennas are safer when working in close quarters around people and are more durable when walking through dense vegetation for wildfire suppression or search and rescue operations. They better for dual-band transceivers because telescoping antennas are usually mono-band.   Dual-band flexible antennas approximate a 1/4 wave on 2 meters and a 5/8 wave on 70 cm, are optimized for one band and may resonate poorly on the other.  How efficient a particular antenna is can be determined only by testing.  

A telescoping half-wave Larsen, or half-wave, dual-band-mobile antenna with magnetic mount, which will work well either with or without a ground plane, and offer the best “bang for the buck.”  A 5/8 wave is also a good choice if you have a suitable ground plane, such as the center of your vehicle roof, or other suitable counterpoise.  
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KB1LKR
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« Reply #4 on: August 16, 2004, 07:11:11 PM »

Shouldn't -5dBd at 5W be ~3W ERP not 1W? 50mW ERP for -20dBd (just over -3 S units!) and 5W looks right though. (In any case -5dB is still minus almost a full S unit.)

Do you have (or any links too) any specific, quantitave, comparitive data for the 17" Comet BNC/SMA-24's vs. 15" Diamond SRH77CA's vs. 17"(?) Pryme RD-98s' vs. other dual band whips at 146 MHz vs 445 MHz?

Is it a safe assumption the 15" Diamond, et al. may have been optimized for 70cm and the 17" Comet, Pryme, et al., are optimised for 2m, or am I way out on a speculative limb?
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RADIOHEAD
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« Reply #5 on: August 16, 2004, 10:46:05 PM »

I'm going hiking out in the boonies for two weeks. So here's what I got so far from you fine folks' reponses: (1) A well tuned wire antenna cut to the exact frequency would be the ideal antenna in this case. (2) The ideal mounting location for maximum radaition would be the top of the backpack. Is there anything else you'd add to this? As I don't have an antenna tuner can I get an aftermarket wire antenna?
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RADIOHEAD
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Posts: 97




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« Reply #6 on: August 16, 2004, 10:55:28 PM »

Would you recommend this antenna?
http://www.centurion.com/home/ant2way/dr.asp

I was looking for the Larsens, but for some reason their homepage wouldn't load on my PC.




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AA4PB
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« Reply #7 on: August 19, 2004, 08:09:01 PM »

Rubber Ducks make better toys than antennas :-)
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