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Author Topic: Are short "dual band" antennas, really d  (Read 1613 times)
K4NFG
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Posts: 45




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« on: March 22, 2008, 12:02:33 PM »

Or do they just happen to work on 2 bands?

I have been looking at short "compromise" vhf/uhf antennas to put on the roof of my car. I was checking into the Larsen NMOQ2/70B (which I realize they don't make anymore) and was wondering what makes an antenna like this "dual band"? Is it because it is somewhat resonant on 440?

How about the longer antennas, like the Larsen NMO2/70B? Same science involved?



I'm just trying to learn the science behind it.

Thanks,
John
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K0BG
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Posts: 10248


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« Reply #1 on: March 22, 2008, 01:24:15 PM »

Here's what you might do. Radiall/Larsen will mail you a current catalog just for e-mailing them and asking for it. There is a section devoted to their "inter-workings". I don't know what the "Q" model is, but the NMO2/70BK is the most popular dual band antenna sold. One of the reasons is it's quality, and ruggedness.

Distractors will say the exhibited gain is not as good as say a Comet, but the truth is, it's a tad better when you toss out the hyped numbers.

By the way, the NMO2/70BK is a 1/2 wave loaded antenna on 2, and a collinear on 70 cm. The power rating is 100 watts, but mine easily handles a 160.

Alan, KØBG
www.k0bg.com
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KB1LKR
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Posts: 1897




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« Reply #2 on: March 22, 2008, 05:55:54 PM »

The Larson NMOQ ("chrome") & NMOQ B (black) are just 1/4 wave whips on an NMO base for 136-512 MHz (user must cut whip to length per the cut chart for desired operating frequency.)

Cut for 2m it will also function as a 3/4 wave radiator at 70cm -- though the pattern will have several high lobes -- but it's basically a single band, tunable whip for general (amateur/commercial/PS) use.

The NMO 2/70 is a dual band antenna, the coil in the middle divides it into coaxial sections on 70cm.  
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KD5RKO
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Posts: 5




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« Reply #3 on: March 27, 2008, 12:16:39 AM »

How about an antenna like the MFJ 1402, small and good for around town usage but the documentation is slim. Anyone know what the mechanics are behind something that small it's 16 1/2" with a coil in the middle section. Can't find any real specs on it though.
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AB8ZL
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Posts: 35




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« Reply #4 on: March 27, 2008, 06:46:17 PM »

I have the Diamond NR72BNMO and I was surprised how well it performs. It is center mounted on the roof of my Bronco and I can hit virtually all the repeaters that my other longer dual band (a NR770HBNMO) can on 2 meters. Its performance on 70cm isn’t quite as good but it gets me into the local repeaters just fine.

It is only 13.8“ tall and rated at 2.15 dB gain on both bands.
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