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Old 07-04-2019, 11:48 AM
GrifterXIII GrifterXIII is offline
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Default Good Antenna for SAR



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As title says in looking food a good antenna for a HAM handy talkie that will be used for Search and Rescue. It will be used in moderate to heavy woodland and possibly some more urban areas too. While I know im going to struggle with signal with elevation and things like that, im just looking foor a good over all antenna that is quality made and wont fail while out on SAR.

Last edited by GrifterXIII; 07-04-2019 at 11:53 AM.. Reason: fix
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Old 07-04-2019, 12:24 PM
Outpost75 Outpost75 is offline
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Years ago the National Institute of Science and Technology tested Public Safety "high-band" VHF and amateur 2-meter antennas. Flexible antennas commonly used on portable transceivers have -5db, “negative gain” compared to a quarter wave whip held vertically at face level. This means that your 5-watt portable VHF with flexible helical antenna has an effective radiated power of only 1-watt. Carrying the portable on your belt produces -20dB of body attenuation, reducing EIRP to 50 milliwatts! UHF results in the GMRS and public safety bands are similar.

Flexible "rubber ducky" antennas are rubber covered helical springs, intended to withstand rough handling, but they are not indestructible. Flexible antennas used on California fire 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.

For SAR you should ALWAYS carry a spare antenna of some type.

An expedient which improves the performance of a flexible antenna is a counterpoise wire (19." long for 2-meter ham, 18” for MURS, Marine, high-band LMR or 6.5" for 70cm ham or 6” for GMRS) of stranded wire, crimped and soldered to a ring terminal for SMA or a battery clip for BNC connector. A battery clip can be clamped onto the shield collar of a BNC connector, or the ring terminal slipped over an SMA connector, enabling you to thread the antenna over it. Reinforce the soldered connection with heat shrink to resist flex.

A wire counterpoise prevents transmitted RF from coupling with your body so that 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." The Ed Fong DBJ-2 (ham) dual band roll up (144-148 MHz and 440-450 MHz) or DBJ-2 (commercial) (152-157 MHz and 460-470 MHz) work well. You can get them from CountyComm, https://countycomm.com/collections/r...overnment-pack or Google Ed Fong's website https://edsantennas.weebly.com/ and buy them direct from him.
Or if you are so inclined you can make your own from his instructions.

The wind-up J-pole antenna rolls up 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 rig to a magnetic mount mobile antenna to provide a clear RF path outside the vehicle. This overcomes about -10dB attenuation 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. Pre-position antennas at shelter sites, casualty collection points and heli-spots,etc. for this purpose.

In marginal operating locations a telescoping, half-wave performs 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 in average suburban ground clutter from about a mile with the stock flexible antenna to 3 miles or more, depending upon your height relative to the terrain. Adding a counterpoise to a unity gain antenna enables a portable unit to maintain reliable contact within 5 miles of an EOC or base station which is equipped with a 5db gain omni-directional antenna 50 feet above ground level.

Telescoping antennas are fragile and work best when stationary or in the open. Avoid side impacts, rough handling or prolonged mobile use of telescoping antennas on auto 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, CERT or SAR search and rescue operations. They better for dual-band transceivers because telescoping antennas are usually mono-band. Most 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, or dual-band-mobile antenna with magnetic mount, which will work either with or without a ground plane, offers the best “bang for the buck.”

Any emergency antenna for your portable transceiver should be rated to handle up to 50 watts of RF output so that it can be used as an expedient antenna to use with a mobile radio in portable operation, or to permit use of an external "brick" amplifier with your portable.

A magnetic mount works best on a car, but an improvised ground plane can almost always be found around the home or office, such as a metal filing cabinet, metal trash can, cookie sheet, rain gutter, refrigerator, window air conditioning unit, balcony railing or any other large metal object. On boats, motorcycles, fiberglass truck caps, ambulance bodies or wooden balcony railings use a half-wave antenna, which does not require a ground plane.
If you need to place an antenna on a bus or other vehicle where a mag mount won’t work, use a suction cup mount: see

http://www.w5fc.org/pse_docs/KNOWLEDGE/qst_p56.pdf

Hope this gives you some ideas.
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Old 07-06-2019, 04:04 PM
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One of the more popular dual-band HT antennas is the Nagoya NA-771. As Outpost said, add a counterpoise to improve it (or almost any other HT antenna).

Depending on how you'll use it and if you'd like to solder a bit, here's one I made. It works better than any HT antenna I've tested it against, with a flat ~1.5 SWR across the 2m band. It's less convenient than one attached to the HT but more convenient than something like a Slim Jim because you can still use it on the move. Instructions here: http://www.tothewoods.net/Comms-how-...dipole-vhf.php



For your use, I might carry this as a backup for when others aren't giving the clear transmissions you need. I just used this in a backpack to help marshal a parade, where I needed to be mobile. Not this pack, but similar.



Quote:
Originally Posted by Outpost75 View Post
Flexible "rubber ducky" antennas are rubber covered helical springs,
I've taken apart several Baofeng antennas recently that are not the normal helical spring. Here's one pic, with more details of what's inside (like the capacitor) at the link.
http://www.tothewoods.net/Comms-Insi...ky-Antenna.php

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