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Commercial Radio Antennas Please keep discussion related to professional, commercially used antennas and antenna systems for the two-way radio industry. Topics for the use of these antennas on amateur bands are accepted here.

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Old 05-12-2014, 7:42 PM
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Default Question about GMRS attic antenna

Hello all, new to the site here!

I have a question in regards to an attic antenna for GMRS. I am obtaining my license and would like to install an attic monted antenna for a base station. The house is a rental and I am not allowed to install anything exterior, but did get the OK to use attic space. I only have maybe 4 feet or so of height right at the peak.

My question is, I have been reading up on antennas and antenna gain. Due to the height, I could only use what they call a unity gain fiberglass base staion antenna. A ham friend of mine suggested finding a large metal or aluminum plate, drill the center and install a 5bd UHF mobile radio antenna in the center, and install that in the attic thus giving me "gain".

What do you all think is the best route and best performer? A fiberglass base antenna or the mobile antenna idea?

Thanks in advance!!
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Old 05-12-2014, 8:27 PM
ermin's Avatar
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Wirelessly posted (Mozilla/5.0 (iPhone; CPU iPhone OS 6_1_4 like Mac OS X) AppleWebKit/536.26 (KHTML, like Gecko) Version/6.0 Mobile/10B350 Safari/8536.25)

Try this

http://www.rfparts.com/catalogsearch/result/?q=SVU4500SP1

73

Ed
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Old 05-12-2014, 8:35 PM
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I recommend an Arrow Dual Band J Pole antenna. It may not have the most gain, etc. but is very easy to install/remove. I used one for several months in an attic setting similar to yours with good results. Moreover, it's a rock solid product that give excellent SWR returns. There's several models available based on your frequency requirements.

Arrow Antennas JPole 2m 70cm Dual Band Repeater FM
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Old 05-13-2014, 8:34 AM
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Some antennas require a "ground plane" and some do not. A typical mobile antenna requires a ground plane to provide the other half of the antenna. A ground plane does not "add" gain to an antenna. Some base station antennas don't require a ground plane. Antenna gain is a function of the antenna design and may or may not require a ground plane. Gain in a mobile antenna is usually achieved by stacking 1/4, 1/2, or 5/8 wave elements on top of each other. Adding a metal ground plane under a mobile antenna would improve its effectiveness. A ground plane needs to be a minimum of a 1/4 wavelength. A base station antenna that uses multiple phased "trombone" or dipole elements doesn't require a ground plane. Gain in this type of antenna is achieved by the multiple phased elements.
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Old 05-13-2014, 5:58 PM
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Thank you all for the advise! Much appreciated!
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Old 05-13-2014, 8:56 PM
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The LairdTech FG4003 is a 5/8 wave stacked omni base antenna offering 3db gain. At a little under 4 feet tall it would fit into your attic, and no ground plane needed with a 5/8 wave. It comes in a 460-470 mHz version to handle GMRS.
http://www.theantennafarm.com/catalo...ries-1058.html

Last edited by popnokick; 05-13-2014 at 9:01 PM.. Reason: Fixed wrong antenna reference
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Old 05-16-2014, 3:07 PM
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The FG400x series are a overpriced fiberglass fixed antenna with 18 gauge steel wire with piss poor copper plating inside.

"5/8 wave stacked" .. who the hell are they kidding.
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