Author Topic: A little afternoon project  (Read 13122 times)

Offline kvom

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A little afternoon project
« on: November 06, 2009, 04:05:50 PM »


It's a mount for a CB radio antenna for the Jeep, that mounts in the same place as the original radio antenna:


Offline Bernd

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Re: A little afternoon project
« Reply #1 on: November 06, 2009, 04:18:12 PM »
Looks like it mounts to somewhere on the side of the vehicle. I would think you would wipe that out in the first time you side swipe a small tree. Or do you try to avoid those small tress and bruch when off roading.  :lol:

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Offline tinkerer

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Re: A little afternoon project
« Reply #2 on: November 06, 2009, 05:00:26 PM »
That looks great. Where does the wire go? Do you just plug it in the nipple on the inside?
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Offline kvom

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Re: A little afternoon project
« Reply #3 on: November 06, 2009, 06:05:54 PM »
It's possible it could get hit.  If so I'll move the mount elsewhere or make a new one.  A branch would brush over (antenna is fiberglass).  In any case it's only am inch off the side.  I put it there as being the only place to mount it not requiring additional holes in the sheet metal.  The alternate spot would be at the rear.

The cable screws into the bottom of the fixture.

Offline websterz

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Re: A little afternoon project
« Reply #4 on: November 06, 2009, 06:35:04 PM »
That looks great. Where does the wire go? Do you just plug it in the nipple on the inside?

Hehe...hehehe...hehe...he said nipple... :lol:
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Offline andyf

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Re: A little afternoon project
« Reply #5 on: November 06, 2009, 07:25:40 PM »
From a radio point of view, it would have been better on the vehicle roof. But there's a downside to that, as I found when driving into a multi-storey car park without removing my ham radio antenna. It must have cost a lot to replace those ceiling mounted fluorescent tube lamps  :lol: :lol:

Andy
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I've cut the end off it twice, but it's still too short

Offline kvom

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Re: A little afternoon project
« Reply #6 on: November 06, 2009, 08:05:08 PM »
For offroad use you don't need as big a range as a truck driver does. Mainly you're just talking with people within a few hundred yards at most

Offline Bernd

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Re: A little afternoon project
« Reply #7 on: November 06, 2009, 08:51:13 PM »
From a radio point of view, it would have been better on the vehicle roof. But there's a downside to that, as I found when driving into a multi-storey car park without removing my ham radio antenna. It must have cost a lot to replace those ceiling mounted fluorescent tube lamps  :lol: :lol:

Andy

Can't believe somebody halfway around the world did that too! I did it with a fiberglass CB antenna. I got about 4 lights before I realized what was happening.

Bernd
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Offline John Hill

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Re: A little afternoon project
« Reply #8 on: November 08, 2009, 03:23:30 AM »
For offroad use you don't need as big a range as a truck driver does. Mainly you're just talking with people within a few hundred yards at most

The size of the aerial is determined more by the wavelength being used than the working distance.
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Offline SKIPRAT

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Re: A little afternoon project
« Reply #9 on: November 08, 2009, 04:50:00 AM »
that is true to a certain extent but an antenna can be wound as a helix round a non conducting former thus shortening it's length whilst still keeping its electrical wavelength the same.The mounting position is also critical
with regards to the preformance of the antenna if mounted low down on the side it will not radiate effectively in
all directions due to the screening imposed by a metal body the best place to mount any transmitting antenna is
in the middle of a metal roof as most mobile antennas rely to some extent on the "groundplane effect" of metal
roofs ,for off road us it is better to have a shorter antenna mounted higher up than a long antenna mounted lower down as it will always radiate better due to it being in free space .

Cheers Paul
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Offline Darren

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Re: A little afternoon project
« Reply #10 on: November 08, 2009, 05:05:30 AM »
For offroad use you don't need as big a range as a truck driver does. Mainly you're just talking with people within a few hundred yards at most

The size of the aerial is determined more by the wavelength being used than the working distance.

I think he was referring to the advantage of roof mounting instead of side mounting and having a box metal box in the way of the signals.
Because of the short distances the effective power loss wouldn't matter.
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Offline SKIPRAT

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Re: A little afternoon project
« Reply #11 on: November 08, 2009, 06:46:09 AM »
all points noted Darren what i was trying to say is that having a transmitting part of an antenna close to metal objects makes tuning the antenna difficult (SWR problems)  when off roading you usually only need a range
of a few hundred yards or so i just thought i would add my little bit on the subject . My other hobby is amateur radio and has been for quite a few years.


Cheers Paul     73 G6FOW
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Offline 75Plus

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Re: A little afternoon project
« Reply #12 on: November 08, 2009, 09:49:11 AM »
 The advantage of roof mounting is that the roof becomes a "Ground Plane" and tends to radiate the signal evenly in all directions. Compared to the side mount pictured which will have the stronger signal in the direction AWAY from the vehicle.

I have used roof mounts for VHF/UHF antennas since they tend to be short. I use rear mount for HF antennas and try to point the vehicle toward the location I am in contact with. Turning away can cause a 3 or 4 DB drop in signal.

73's n0fnf

Joe

Offline John Hill

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Re: A little afternoon project
« Reply #13 on: November 08, 2009, 03:04:30 PM »
No doubt about it the centre of the roof is the ideal spot for a VHF whip antenna but if that is impractical because of bushes, trees, low garage roof etc (or if the roof is fibreglass) another really good spot is smack bang in the middle of the bonnet ('hood' for those rebel colonists) but you will need a wire braid to ground the bonnet to the rest of the body and of course good shielded cable within the engine compartment. 
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Offline kvom

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Re: A little afternoon project
« Reply #14 on: November 08, 2009, 03:47:03 PM »
The Jeep has no roof, but rather a DOM tubing roll cage.