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Author Topic: looking for help with 2m antenna options  (Read 2025 times)
NEVBEN
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Posts: 43




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« on: January 05, 2012, 09:14:52 AM »

I have an offroad vehicle with a large aluminum roof rack.  looks like this:  http://www.expeditionportal.com/forum/attachment.php?attachmentid=50932&d=1292688327

The rack might be a decent ground plane itself.  The roof underneath it is steel but has two glass sunroofs.

I will drill all the holes needed.

I want to mount a high gain antenna, like a 5/8 wave.

I'm looking at Larsen 150 or 2/70 (I won't have UHF radio though)

or

a center-loaded 5/8 like the Comet SBB25

a single 5/8 is my height limit because there's overhead lines around town.  In the bush I need manual fold-over capability which I can either buy on the antenna or fabricate into the bracket.

I will probably play with the mounting and a SWR meter, but what should I buy to start with?

Should I mount on the steel roof and come through the roof rack?  Or mount on a bracket in the center of the roof rack and ground strap it?  Just use a coil?
« Last Edit: January 05, 2012, 09:17:04 AM by NEVBEN » Logged
K6LCS
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Posts: 1552


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« Reply #1 on: January 05, 2012, 09:33:52 AM »

How much "abuse" does your vehicle receive?

Clint Bradford K6LCS
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Clint Bradford, K6LCS
http://www.work-sat.com
NEVBEN
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Posts: 43




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« Reply #2 on: January 05, 2012, 09:43:57 AM »

A ton.  I stay on established routes but it still sees a lot of brush, overhead branches, rock crawling, and gets pounded on the whoops in the desert.

I'm thinking I will either have the antenna fold-over so that it is below the roof rack, or I will have a bracket that folds over and has a little "ramp" underneath so branches will slide up the ramp rather than try to rip off the bracket.

I could also go to the rear bumper, or 1/4 wave but I'd like to have height and gain to reach the repeater from the canyons.  I'll just carry a spare whip.
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WB6BYU
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Posts: 13334




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« Reply #3 on: January 05, 2012, 01:04:13 PM »

I'd recommend an NMO mount with both a 1/4 wave whip and a 1/2 or 5/8 wave available
to use when circumstances permit.  Though I have to say, having run a lot of A/B testing
on antennas while driving in difficult coverage areas, the 5/8 wave whip only gives a slight
improvement over the 1/4:  perhaps the difference between 40% copy and 60% copy.
The variation in signal strength as you drive down the road is much higher than the
difference between the two antennas.  You'll have to run your own experiments to see
which works best for you, but since it would be a good idea to carry a spare whip anyway
in that kind of use, it won't hurt if they are different types.  If you only have one antenna,
the 1/4 wave whip isn't a bad choice because it is more rugged.

Look for antennas that have a single continuous flexible whip coming out of the base
rather than something with joints, plastic-cased coils, or any significant mass high up
on the antenna.
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AI7RR
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Posts: 164




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« Reply #4 on: January 19, 2012, 03:05:05 PM »

Assuming that's the rack on your vehicle, I'd suggest a mirror mount style NMO mounted on the front rail and as stated earlier, with your basic 1/4 wave vertical. Make sure you use a spring and pay particular attention to protecting the feedline.

73, Roger
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KD8RFT
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Posts: 29




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« Reply #5 on: January 22, 2012, 02:46:11 PM »

Love my larsen nmo 2/70. Dad still has his larsen mag mount from the seventies
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