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 Post subject: UHF in a Dmax
PostPosted: Fri Jul 27, 2018 8:03 pm 
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Joined: Fri Dec 20, 2013 6:32 pm
Posts: 92
Location: Brisbane
I wasn't happy with most mounting points for a UHF, the cabin is full up really.
All I wanted was a temporary mount so it's easy to remove, I made this mount up using a GoPro suction grip.
It uses a lighter connection in the glove box for power.
I don't have a bullbar so I bought a magnetic aerial for the roof and shortened the coax down to 2 meters long.
Some say you can't shorten coax but I rang a Uniden Tech, he said it's OK.
The mic is mounted on the door, it looks strange but works well.


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 Post subject: Re: UHF in a Dmax
PostPosted: Sat Jul 28, 2018 8:57 am 
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Joined: Wed Feb 05, 2014 1:22 am
Posts: 583
Location: adelaide hills
How long is your arm?

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If it ain't broke, fix it til it is.


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 Post subject: Re: UHF in a Dmax
PostPosted: Sat Jul 28, 2018 10:25 am 
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Joined: Sat Oct 12, 2013 5:36 pm
Posts: 1392
Won't the radio get very hot if used when the sun shines? In Qld their is a bit of that.

Seeing the radio is partially above the LHS airbag and also near pillar airbag, if fitted, I probably wouldn't have it there.

Regarding the coax length, "shorter than what length"?, the folklore speak and reality are quite different, the belief you can't shorten a coax is often said. That would mean you can't have a coax longer either. Perhaps the people who believe that, have wondered how the aerial at the top of a tower gets fed it's signal.
Jaycar sell coax cable of various specs on reels, 30 metres not uncommon, from which you cut the required length for the application. If you can't shorten it we would have a full reel to tuck under the dash.
So if you can buy a long length for a tower install, how can it be that you buy a supplied length with you radio as a kit? They simply decide on cost how long a bit of cable you will get. The length of cable does reduce the overall exit power, shorter better, longer less output at the aerial from same radio of 5W.

I have never seen a radio operater a couple of metres down from the top of a tower clinging to the mast and talking into a mic.


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 Post subject: Re: UHF in a Dmax
PostPosted: Sat Jul 28, 2018 11:20 am 
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Joined: Thu Apr 19, 2018 8:45 am
Posts: 20
Location: Canberra
Shorter is better.

The most common type of coax used in mobile UHF installs is RG-58/U, mostly because it's cheap but also because has a small diameter, so it's easy to route through vehicles. While its performance is perfectly fine at low frequencies (old 27MHz AM CB), it's VERY lossy at UHF CB frequencies (477MHz). There are much better alternatives available (e.g. Times LMR-200) but they're more expensive.

Between 450-500MHz, RG-58/U (proper U.S. mil spec stuff) it has a nominal attenuation of around 10.5dB per 100ft. The cheap Chinese shit is generally worse. This means over a 10 foot run, about 1.1dB is radiated by cable as heat, so of the 5 watts or so of power produced by your transmitter just under 4 watts will actually reach your antenna.

There are situations where coax lengths are critical, but none of these are relevant to installing a UHF CB in a vehicle. In the eyes of your average 4WD accessory fitter or auto electrician, RF is black magic. Few of them have any idea at all. And almost none have the equipment to correctly test any of their RF handiwork, much less any idea of how to use it.


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 Post subject: Re: UHF in a Dmax
PostPosted: Sat Jul 28, 2018 3:49 pm 
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Joined: Sat Oct 12, 2013 5:36 pm
Posts: 1392
Thanks WW
That info is good to see. Clears up some misconceptions often held by 4wd ers.


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 Post subject: Re: UHF in a Dmax
PostPosted: Tue Jul 31, 2018 9:34 am 
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Joined: Tue May 10, 2016 7:43 am
Posts: 367
Location: Gippsland Vic
Sounds like you should of just bought a good hand held


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 Post subject: Re: UHF in a Dmax
PostPosted: Tue Jul 31, 2018 10:07 am 
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Joined: Sat Oct 12, 2013 5:36 pm
Posts: 1392
A good handheld can be better than a bullbar mounted aerial. My GME 5w handheld with a better antennae has far better performance than one on a bullbar. For distance rx and tx, up on roof is better for in vehicle use than a bullbar mount any day.


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