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1loudLX
05-11-2011, 04:19 PM
Coming back from cm, daniel was able to pick up folks on 70 near grand junction while I didn't pick up anything. I was wondering if anyone would be interested in helping me tune it for better performance?

CardinalFJ60
05-11-2011, 05:36 PM
I was picking up Daniel near "castleton"?? while I was on 70 near GJ (maybe 40miles away from GJ).

we were on simplex and I had my biiiiiiiiiiig high gain Diamond SG7900 antenna on the roof of the 60 at high power (50w). that antenna is like 57" tall.

What was interesting is that I didn't really pick you guys up until I was close to the border. I suspect that there was a break in the mountains/canyons that funneled the signal perfectly for a line o' sight rx. If I went around a bend or into a gulley I either didn't hear you, or it got scratchy.

What antenna setup do you have? I think it's more about the antenna than the radio in this situation.

rover67
05-11-2011, 06:09 PM
FWIW when I was chatting with you guys on the way back you were much harder to hear than Daniel. A lot of the time I could only hear Daniel's part of the conversation.

I don't really know how to tune these doodads but you might be able to do better on transmit also.

What antenna do you have? Where is it mounted?

What power were you running on the way back?

1loudLX
05-11-2011, 07:11 PM
Well I've got two, and I had the shorter one on. I think i left it on low power for the drive back. I did try my larger antenna, the diamond nr770b I believe it is when we were still in Utah and still couldn't hear the people daniel was talking to.

My antenna is mounted to a bracket bolted into the door jamb on left side of the hatch, I'll get a picture when I can

rover67
05-11-2011, 08:01 PM
cool, that sounds like a good setup. I run something very similar and it works pretty well.

I wonder if it is some sort of a ground issue... Maybe Dave can chime in :)

I know that the bikes on top of my truck really jacked with my radio in terms of receive quality and transmit "ability".

xodeuce
05-11-2011, 10:42 PM
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.

RockRunner
05-13-2011, 09:59 PM
OK so I broke my base on my antenna during CM and need to get a new one. I have the 8800 in my rig, what is the best antenna to get for range and clarity?

RockRunner
05-13-2011, 11:44 PM
Broke the plastic base that screws onto the mount. kind of disappointed that it broke so easily. I would think I could buy a new base for it but would like an antenna that would bend if it hits a branch or ???? I figure I will repair the Larson and use it for the Dodge and get another one for the Toy. Any suggestions on one that will fold if hit??