UHF Radio and Aerial Mounting

goldcoaster · Senior Member

UHF Radio and Aerial Mounting

Phil C · Guru

Hi goldcoaster

From experience the antenna should be mounted as high as possible, if its a ground independant that can be any place on the roof, roof rack etc. If it needs a ground plane (the package should tell you) then it need metal around the base.

I have the large fibreglass style on the top of my ute rail (behind the cab) the fibreglass is just a "radome" or cover which protects the bits inside, from the amount of bugs on mine its a good investment. From memory you can get 6db or 9db antennas, be careful the propergation patten is different in these and may be a problem in hilly regions. Check google to be sure of your choice, I have a 6db as the patten is flatter.

Safe travels

goldcoaster · Senior Member

Thanks Phil
I haven't bought one yet , looking for recommendations , but from what you have said correct me if I'm wrong, aerial really needs to be unobstructed. So maybe side mirrors and high enough to clear roof . Cheers Mick

Phil C · Guru

Hi Mick

In my opinion the arial needs to be at the highest point of your rig. Sometimes this is not practical but its worth the try.

Have a look at uniden website it may give you some more clues. UHF is a "direct line of sight" signal system, and obstructions can cause degridation or total loss of signal. The website will give you the distances etc.

Its not critical which antenna you buy as long as it is tuned to 477MHz (uhf CB) and does the job for you.

Safe travels

Umpie1 · Senior Member

A small tip from a fellow CB'er. When you have the aerial mounted, run an earth wire from the aerial to the chassis. Sometimes aerial mounts pick up corrosion and interfere with the earthing. This should solve that problem.

Phil C · Guru

Here is my CB ant rig.

I will try that earth wire, sounds like a great idea.

Cheers

Cloak · Guru

That's spot on Phil.... Maybe you should re-muster to radtech...

Phil C · Guru

Cloak wrote:
That's spot on Phil.... Maybe you should re-muster to radtech...

Air or ground mate?

Radar · Guru

Hi All

One thing I don't like about mounting CB aerials on review mirrors is that can and will cause the mirror to come loose because of the weigh, hitting branches of trees, low building and so on.

Not being qualified to speak in great deal about this subject and how they work but from experience of late changing tugs I mounted mine back on the bull bar as it has a spring and then a shinny bit on bottom below the heavy black aerial. I have placed the aerial to the far side and on the base of the bull bar, it sort of acts as a that,s how wide the car is. There it has a very good earth which is very important more so then where you place it. In short where it is place has limits to the direction of the aerial. eg you may get 4 ks that or 5 ks this way.

I like it there as I don't need to watch it bounce around while I am driving, I going to mount the telephone one on the driver side.

Now the ex RAAF radio guy [who now teachers radio Technics] that suggested this place for the aerial said the spring, shinny bit has nothing to do with the over all performance of the radio being below the bars of the bull bar. He did go to great lengths to explain in detail but I said "hay just want to say hello to the guy over there not ten miles away"

Most times on trucks they are hanging off much thicker metal on the mirrors. I did have a Japan built truck back a few years ago and after about 4 years I needed some panel work to hold the mirrors more firmly from having aerials attached.

Phil C · Guru

Radar wrote:
Hi All
One thing I don't like about mounting CB aerials on review mirrors is that can and will cause the mirror to come loose because of the weigh, hitting branches of trees, low building and so on.
Not being qualified to speak in great deal about this subject and how they work but from experience of late changing tugs I mounted mine back on the bull bar as it has a spring and then a shinny bit on bottom below the heavy black aerial. I have placed the aerial to the far side and on the base of the bull bar, it sort of acts as a that,s how wide the car is. There it has a very good earth which is very important more so then where you place it. In short where it is place has limits to the direction of the aerial. eg you may get 4 ks that or 5 ks this way.
I like it there as I don't need to watch it bounce around while I am driving, I going to mount the telephone one on the driver side.
Now the ex RAAF radio guy [who now teachers radio Technics] that suggested this place for the aerial said the spring, shinny bit has nothing to do with the over all performance of the radio being below the bars of the bull bar. He did go to great lengths to explain in detail but I said "hay just want to say hello to the guy over there not ten miles away"
Most times on trucks they are hanging off much thicker metal on the mirrors. I did have a Japan built truck back a few years ago and after about 4 years I needed some panel work to hold the mirrors more firmly from having aerials attached.

spot on mate, it is good for 10KMs on the bullbar. Im a bit of a perfectionist so I put mine up top.

No biggy, its all about what we want and where we want it.

Cheers Radar (love that handle) K band?

Gundog · Guru

Just a bit of additional info best location for any antenna is the centre of the vehicle which gives stronger all round directional lobes, in the old CB days if you didn't want to drill a hole in the centre of the roof, many opted for a single roof bar and mount the antenna on that, it was then found by truckies that the trailer often reduce or blocked signal somewhat backwards. their solution to this problem was to mount an antenna on both mirrors (hence the term twin truckers) this improved their reception distance in all directions but the critical part of the setup was that both cables from the antenna's to the T piece had to exactly the same length.

When I set mine up I will use a similar setup with a pair of centre loaded 6dBi antenna on each side of the cargo barrier on the ute.

Radar · Guru

Gundog HI

Look with out trying to upset you twin truckers are what broke my doors on my 1976 japan made prime mover. For a start they did have a dead spot it was when I was directly at right angle to the base station. Regularly of a night coming home from my Sydney loading base back to good old Gosford I would call up 2 base stations one at Hornsby maned by Kevin and the other at Berowra a lady by the name of Elaine both would would tell me there was break down in the signal as I went along the Highway so one night I was coming home I changed the cord to one aerial only and never had a problem, clear as.

Of interest I still have the first CB set I brought back in the early seventies along with arrangement of aerials that I have collected from over the years, some like spears. the really long ones, the adjustable and short ones along with a couple of other CB sets.

With Am Cb the signal went up in the air and back down like but with UHF the signal radiates out and depending on the terrain indicates the distant of how far you, I don't think twin truckies are going to make much difference

I don't think 2 aerials on your roof are going to be any better but if that is what you need go ahead I am mostly a perfectionist but I am simple person also and one aerial get me where I need to be.

The nick name come about from working to long in road transport, from knowing where most things are, over the 24 years mostly around South East Queensland there isn't much I didn't know after working in yards with high turn over of drivers I was called on a lot to explain to them how to get there. Some I would of preferred to put on a plane and sent back, it would of been easier. Ralph

03_troopy · Guru

Phil, just one point on your antenna mount if i may. The area I have circled on your pic shows loops of cable. It looks like you have looped the excess cable inside the the headboard frame to keep it out of the way. This is not the best for the performance of the rig mate, and can cause signal attenuation. Better to trim excess cable so that it doesn't have the loops, but is still long enough incase you need to reterminate the cable in the future.

As for grounding the base, it's not relevant on ground independant antennas and will make no difference. Grounding the mount is only really required for antennas that require a ground plane.

Ex RadTechA biggrin

PeterD · Guru

Radar wrote:
1, Look with out trying to upset you twin truckers are what broke my doors on my 1976 japan made prime mover. For a start they did have a dead spot it was when I was directly at right angle to the base station. Regularly of a night coming home from my Sydney loading base back to good old Gosford I would call up 2 base stations one at Hornsby maned by Kevin and the other at Berowra a lady by the name of Elaine both would would tell me there was break down in the signal as I went along the Highway so one night I was coming home I changed the cord to one aerial only and never had a problem, clear as.
. . . snip , ,
With Am Cb the signal went up in the air and back down like but with UHF the signal radiates out and depending on the terrain indicates the distant of how far you, I don't think twin truckies are going to make much difference
2, I don't think 2 aerials on your roof are going to be any better but if that is what you need go ahead I am mostly a perfectionist but I am simple person also and one aerial get me where I need to be.

Here comes my theory lesson for the day. For those who don't like technicalities then bugger off, your comments are unwelcome. You don't have to read this post.

Part 1. We are talking 27 MHz CB at this stage. When you are feeding 2 antennas you can get beam forming techniques. That is how those UHF TV antennas with a grid reflector and bow tie antennas in front work. So back to 27 MHz - See this link, I will be referring to figure 1. They are talking about changing the frequency so that the wave length distance between the antennas increases in the subsequent diagrams (commencing from the top left.) You also can get the the same pattern effect by shifting the two antennas apart.

The top LH diagram is your truck with its twin antennas fed in phase. The antennas each radiate the same sort of pattern but it is spaced a little in distance. In the far field distance the two signals react with each other. When the two signals are in phase the two signals add together and produce a much stronger signal than either of the individually radiated signals. Where the two signals are out of phase (ie the peak of the waveform of one is positive and the other is negative) the two signals will cancel each other out and a receive antenna does not receive anything.

In that first diagram the truck is pointing from right to left (or left to right.) As you can see the maximum signal is radiated up and down the road. You can see that the radiation to the sides of the road is a lot less. That was the effect Radar talked about when the base stations could not hear him very well. If you look at the second diagram you can see that as you shift the antennas apart the signal pattern becomes much narrower, the effect is that you radiate a stronger signal down the road and even less to the side.

Part 2. We are now talking UHF CB. Quote, "I don't think 2 aerials on your roof are going to be any better." In fact figure 1 shows why using two antennas on the UHF CB bands is a Richard cranium of an idea. When you get up to 476 MHz the wave length is around 630 mm. If you are spacing your two antennas across the top of the vehicle and even out onto the out-rigged mirrors you will be seeing radiation patterns like those in the bottom row of figure 1. You will note a lot of holes in the radiation pattern. As radar found even on 27 MHz a single antenna can be much better.

Radar · Guru

Hi Peter D

I am trying to get my uneducated head around it all, your link is very good.

I think that is what I was trying to explain without tech know how but years of road experience using and fixing CBs in trucks making them work mostly by changing a fuse, finding a break in the aerial cords and the like?

My new friend said aerials are black magic.

With my aerial on the left side of bull bar its performance is very good.

Hope we all have learnt something. Ralph.

Peter_n_Margaret · Guru

I use the little rubber zero gain antennae on the OKA, mounted top centre front, on the roof.
They give a very clear reception over 5 - 10 km which is plenty.
The last thing I want is to hear everyone for a 30km radius, but clarity is important. These little antennae do that very well and they are also cheap and almost indestructible.
For possible long range emergency use, we also carry a high gain antennae which can screw into the same base., but I have never needed to use it.

05-07-22 07c2E.jpg

Cheers,

Peter

Radar · Guru

Hi PnM

Yes I am also very in favour of using these small short aerials and have on most of my own trucks dating back to the mid eighties when the switch from AM CB to UHF CB was taking place.

I liked using the smaller aerial for convoy work, 4 wheel driving, but when I was setting up this truck I forgot about it and used the big aerial of my previous tow car.

I like your thinking which is very practical using the small aerial for day to day use switching to the taller aerial when needed.

Enjoy your travels. Ralph.

-- Edited by Radar on Sunday 26th of October 2014 10:10:46 PM

goldcoaster · Senior Member

Thanks guy's but as usual I got lost in the Technicalities but have some idea what your talking about . Obviously the radios are all similar as no one has made a recommendation but the Aerial and its location is the most important.

All I really want is to be made aware that the truck behind wants to overtake me , as I will be towing a Suzuki behind motorhome.

I don't want to drill holes in rooftop ,so my two choices were Bull bar or Side mirrors ,now it might be too much weight on mirrors so I will mount on Bull bar.

My next questions , Right side or Left side of bull bar is one side better than the other ? , also long or short aerial ?.

Thanks again

Mick

Santa · Guru

goldcoaster wrote:
Thanks guy's but as usual I got lost in the Technicalities but have some idea what your talking about . Obviously the radios are all similar as no one has made a recommendation but the Aerial and its location is the most important.

All I really want is to be made aware that the truck behind wants to overtake me , as I will be towing a Suzuki behind motorhome.

I don't want to drill holes in rooftop ,so my two choices were Bull bar or Side mirrors ,now it might be too much weight on mirrors so I will mount on Bull bar.

My next questions , Right side or Left side of bull bar is one side better than the other ? , also long or short aerial ?.

Thanks again

Mick

Morning Mick, virtually any UHF antenna will do what you require, I use something similar to this

http://www.bcf.com.au/online-store/products/GME-UHF-Antenna-AE4012K2.aspx?pid=117518#Cross

The price seems pretty high to me, I'm sure there must be better deals around.

Try your local Dick Smith or Jaycar store, as long as its a reputable brand, my only concerns would be ease of installation and size, no need for roof top mount, something like I use mounted either side of the bull bar will get you a few kilometers in all directions without a problem. wink

Radar · Guru

Hi Mick

Bull bar either side. 600 long spring loaded.

Mirror smallest aerial you can get maybe a light weight wire one, they are cheap will do the job, my last company I worked for would of had a list 40 of these type about 400 long on there truck

www.antennaagencies.com.au

This company is at Banora Point, I am with some success using one of there aerials for our mobile telephone, they do have assortment of aerials and they may help you in selecting the better one for your needs as they will be able to see where you would like to place it if you take the mobile home to them.

Phil C · Guru

03_troopy wrote:
Phil, just one point on your antenna mount if i may. The area I have circled on your pic shows loops of cable. It looks like you have looped the excess cable inside the the headboard frame to keep it out of the way. This is not the best for the performance of the rig mate, and can cause signal attenuation. Better to trim excess cable so that it doesn't have the loops, but is still long enough incase you need to reterminate the cable in the future.

As for grounding the base, it's not relevant on ground independant antennas and will make no difference. Grounding the mount is only really required for antennas that require a ground plane.

Ex RadTechA

Yeah I agree Troopy, its a very temporary measure till I get some decent BNCs.

So far, touch wood, not too much degradation still getting and sending a 5 by 5.

Thanks for the input

goldcoaster · Senior Member

Thanks Radar and Santa , maybe santa will bring me one. Thanks to all who replied. Mick

normn · Member

PeterD, you weren't at the radio lab by any chance?

Norm

PeterD · Guru

Radio lab, you are talking PMG are you? I started with DCA.

exa41 · Guru

what part of DCA were you Peter , I worked at OPs on the runways for 8 years .

PeterD · Guru

Trained in the RTTS Sydney, then various postings in NSW and TPNG as a radio tech. When DCA became part of Aviation & Transport I jumped ship and went to the AGs in ACT.

moblet · Senior Member

goldcoaster wrote:
Obviously the radios are all similar as no one has made a recommendation

My understanding is that radios differ in their sensitivity but that these differences are insignificant for your purposes, i.e. communicating with traffic in the immediate vicinity. For your intended usage something cheap like a Uniden would be fine.

Another way in which radios differ is in their tuning and control knobs and buttons. If you're going to leave it locked on the highway channel most of the time then it's not going to matter if it's a pain in the neck to change through 20 channels.

There are different antennae for different terrains but again, for short range communication the cheapest option will do the job.

Instinctively I'd expect the motorhome body to block signal from the rear with a vertical bullbar mount. I've seen a few motorhomes set up this way but never asked their owners about radio performance. Mounting as close to the edge of the bullbar as possible might work. As to which side, on the left it's less likely to distract you or interfere with vision but is more vulnerable to damage from vegetation and passing vandals when parked in towns.

This retailer claims that different antenna constructions may be required for different vehicles, mounting points and road conditions. Again if you're not doing anything extreme the cheapest option will suffice.

-- Edited by moblet on Friday 7th of November 2014 11:08:43 AM

-- Edited by moblet on Friday 7th of November 2014 11:09:00 AM

Knowledge speaks, but wisdom listens.