Thread: 8800 tuning
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Old 05-11-2011, 10:42 PM
xodeuce xodeuce is offline
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Join Date: Jan 2011
Location: Alabama
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Quote:
Originally Posted by CardinalFJ60 View Post
What antenna setup do you have? I think it's more about the antenna than the radio in this situation.
Bingo.

The Diamond NR770 is a 1/2λ on 2M. If my memory serves me from riding behind Daniel on 7 Mile Rim, he has the Larsen 5/8λ 2M whip.

Gain figures on 1/2λ vs 5/8λ are roughly 3.8dBi vs 5.2dBi, in dBd it's 1.6 dBd vs 3.0dBd. Across the board, a 5/8λ will get you better directional performance in a horizontal plane, as you're flattening the torus of its radiation pattern. Think of antenna gain as you would an attachment on a garden hose. You can put on a fan type sprinkler, and put out water at low pressure over a wide area, or you can put on a nozzle and put out the same amount water at high pressure over a narrow area and greater distance. Gain works the same way. You're not creating any more signal, you're just radiating it into a different and more concentrated pattern. A 5/8λ radiation pattern is a flatter torus than a 1/2λ, which is flatter than a 1/4λ.

If properly RF grounded and tuned to low SWR, the 5/8λ should outperform the 1/2λ in a similar setting. However, if you can't get it to tune, your ERP on the 1/2λ would actually be higher. It all depends on your antenna system and grounding. Ideally you want to drill a hole in your roof and do an NMO stud permanently installed. I finally got over the jitters and did that in my Tacoma, and it's been leak free from day one. If you use a Larsen NMO mount antenna it is actually double o-ring sealed, and if you want to take it off there's a weather cap that also has a double o-ring seal. Best of all, it just looks like a sat radio or GPS antenna with the weather cap. Obviously this depends on roof rack and other things though as to how well it will tune up. My roof is naked except for the antenna for the time being, and I'm sub 1.5 SWR across 2M. With the Larsen 5/8λ though, you DO have to cut it to length to get the SWR down. It is a little long to start with IIRC. The antenna will come with a chart to specify the length based on installation location. It varies depending on how close to ideal the ground plane is. I think they give you two lengths, fender and center of roof. I would expect a lip mount on the hatch to be similar to a fender mount, assuming it was well grounded and the the hatch had a braid ground strap to the body.
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