<span class="highlight">Antenna</span> location Question.

Submitted: Sunday, Mar 15, 2015 at 08:59
ThreadID: 117070 Views:2462 Replies:7 FollowUps:6
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I am aware that having a uhf antenna mounted in the centre of the roof turret gives better radio performance than the more popular bull bar mount.

My question is if i mount the antenna to a roof bar or roof rack close to the roof centre will i improve radio performance simliar to mounting the antenna directly into the centre of the roof turret,??? also if i mounted an external phone antenna the same way would the phones performance be enhanced ??
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Reply By: Nomadic Navara - Sunday, Mar 15, 2015 at 10:08

Sunday, Mar 15, 2015 at 10:08
The edge location will not be as good as a central location. However the height advantage will give a significant performance advantage over bull bar mounting.
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Follow Up By: Tim F3 - Sunday, Mar 15, 2015 at 10:32

Sunday, Mar 15, 2015 at 10:32
Peter thankyou for the reply,my intention is to mount it in the centre of the roof bar as close as possible to the centre of the turret.
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Reply By: Bob Y. - Qld - Sunday, Mar 15, 2015 at 10:42

Sunday, Mar 15, 2015 at 10:42
Tim,

From my experience, the higher you can mount the antenna, both UHF & phone, the better the performance. Positioning would be of secondary importance in most cases, in a mobile situation.

Just depends on how low your garage door is too. :-))

Bob

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Reply By: pop2jocem - Sunday, Mar 15, 2015 at 11:18

Sunday, Mar 15, 2015 at 11:18
The reason I, and probably a lot of others, mount their aerials on the 'roo bar is because even though there is some trade off performance wise, the chances of aerial damage is somewhat reduced.
Personal experience, I had one mounted on a roof rack. Forgetting it was there I wiped it off going under some low hanging branches.
I know you could damage a 'roo bar mounted one, but at least you are reminded it is there by being in your your line of vision.
I am not sure how true it is but I was told that the transmission and receiving range is greater to the front or back of your vehicle if mounted at either the front or back of your vehicle.
What I am trying to say is that if it is 'roo bar mounted for example, you loose range in the forward direction but gain in the rear, if that makes any sense. Or maybe it was the other way around. (Insert confused emoticon)
I would think the length of the aerial would also come into the equation. Mine is about 1600 mm long total. Whether this is good or bad I have no idea but it works for me.
These days I mainly use mine when caravaning to listen out for any chatter on the truckie's channel.

(:=))

Cheers
Pop
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Reply By: Sand Man (SA) - Sunday, Mar 15, 2015 at 19:29

Sunday, Mar 15, 2015 at 19:29
Tim,

Unless you wish to put up with a "wank pole" mounted to the bullbar and annoying you and your passenger, I would suggest you take a look at a mudguard mounted one such as this RFI one from Prestige Communications

I have an earlier model stainless steel one mounted on a stainless steel bracket between the mudguard and bonnet and the top reaches above the roof line. Fairly unobtrusive but still gives excellent performance.

Bill


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Follow Up By: pop2jocem - Sunday, Mar 15, 2015 at 19:37

Sunday, Mar 15, 2015 at 19:37
So Bill, these "wank poles" of which you speak.
No good?
You knowing a bit about the subject.
Please explain.
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Follow Up By: Sand Man (SA) - Sunday, Mar 15, 2015 at 20:16

Sunday, Mar 15, 2015 at 20:16
Pop,

I didn't say the "wank poles" are no good.
What I am alluding to is the thick (usually white) fibreglass antennas are a distraction to the view out the front windscreen, swaying in the airflow. I have travelled in a vehicle sporting one and I didn't like it.

In my opinion, a ground independent antenna, mounted on the mudguard area close to the windscreen and with the top of the antenna high enough to clear the roof line of the vehicle, is as effective and efficient as one mounted on the bullbar and much less obtrusive. Mine is rated at 6db which is a good all round compromise to suit the majority of situations.

A convoy of three vehicles I was part of, were traveling down the Strzelecki Track one time and we came across a road work crew with a grader which had shed a tyre. They asked us if we could contact their base for support as we got closer to civilisation and we kept trying as we traveled down the track. Eventually, I established contact and at the same time, another member of our convoy, with a fibreglass "wank pole" also heard and could respond to the conversation.
This established to me that my 900mm stainless steel RFI antenna was just as effective as my mate's 2 metre white fibreglass pole mounted on his bullbar.

Both styles of antennas, mounted in their respective locations, will do the job and each of them are easy to connect the coaxial cable to, without cable routing problems up the window column or whatever, to one mounted on the roof area.

I personally just don't like the bullbar antenna location, although I will admit to mounting a safety flag to my bullbar for relatively short periods from time to time.
Bill


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Reply By: Eric Experience - Sunday, Mar 15, 2015 at 21:06

Sunday, Mar 15, 2015 at 21:06
Tim.
The reason the roof center mount is the best is because that is place where the electrical noise generated by the vehicles electronics is minimum. A ground independentantenna would be needed on the roof rack because the normal dipole uses the roof as part of the antenna. A 100 mm high antenna on the roof will out perform a yobo stick on the bull bar when it comes to receiving distant signals. Eric.
AnswerID: 550032

Follow Up By: Nomadic Navara - Monday, Mar 16, 2015 at 09:42

Monday, Mar 16, 2015 at 09:42
The roof centre is used because:

1. It provides the best area for a ground plane.
2. There are no obstructions to interrupt the transmission of the radio waves.
3. it gives you the maximum height without installing a mast.

The first point may not be important with ground independent antennas but the second point is equally important. If there is electrical noise that effects the reception shifting the antenna up to the turret will do little to relieve the problem, you need to suppress the noise at its source.
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Reply By: Eric Experience - Monday, Mar 16, 2015 at 21:22

Monday, Mar 16, 2015 at 21:22
Peter D
I recommend you do some testing before making statements. If you get a hand held uhf with manual squelch control you will find a considerable reduction in interference in the center of the roof. Those who install radios for a living in police and Ambulances vehicles are subject to legal action if they get it wrong so they always use the small antenna in the roof center. Eric
AnswerID: 550077

Follow Up By: Nomadic Navara - Monday, Mar 16, 2015 at 21:44

Monday, Mar 16, 2015 at 21:44
I have had experience. I spent many years installing police radios and AM 2 way radios on airport equipment. What gives you the right to question me?
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Reply By: michael k7 - Wednesday, Mar 18, 2015 at 01:32

Wednesday, Mar 18, 2015 at 01:32
I can't speak for all the other knowledgable people here but with the three different locations I have used for UHF
1. On the bulbar fibreglass aerial was good can here clearly about 20k but as said before it also drives me nuts.
2. On the windscreen with a short 2foot wire aerial just about useless
3. On the mudguard between the bonnet and guard with a bracket with a metre wire aerial with a larger base then a spring then straight this has been my best reception.
Everybody to their own ideas but just remember putting it on the roof you will go through a few aerials plus at service stations I can remember when I was young with CBs smashing the light tubes haha
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Follow Up By: patrolman2 - Sunday, Mar 22, 2015 at 21:00

Sunday, Mar 22, 2015 at 21:00
I have used CB radio since the late 70's,starting with the old 27mghz and now with UHF. Without doubt a centre of roof aerial will give a better output signal than sitting on the bulbar.On the guard is usually better than the bulbar,but will be more directional across the bonnet side.There are reasons for this but I am not an electronics guru.There are stainless steel brackets you can purchase to bolt onto the guard while still being able to shut the bonnet. In my experience,I have found these brackets tend to vibrate on rough roads and can damage both the edge of the guard and the edge of the bonnet.I have mine mounted on the bulbar for convenience but have made certain it is on the driver side of the vehicle to prevent the cook complaining when a photographic opportunity presents itself from the front nearside of the vehicle.Don't worry about people thinking you are a wanker with a bulbar mount.Do what you are comfortable with and what suits you. Aerials these days are also much more refined and more efficient and will give you acceptable results wherever they are mounted.
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