UHF antenna placement and "ground"

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UHF antenna placement and "ground"

Post by mahna » 06 Oct 2014, 12:32 pm

I've got a UHF radio on the way for the ride, looking for advice on the best mounting position.

I'm lead to believe where the antenna is mounted in relation to the truck body plays a part in signal quality by providing a "ground" for the signal?

Front quarter panel is most common place, is this the best or just convenient?

Thanks guys.
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Re: UHF antenna placement and "ground"

Post by Combat_Wombat » 06 Oct 2014, 12:59 pm

Do you have a bullbar mounted on? I just installed one this morning
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Re: UHF antenna placement and "ground"

Post by Apollo » 06 Oct 2014, 2:00 pm

The above photo is probably the worst place you can mount any antenna. The base is not above metal work and it's to one side which will react with the operation of the antenna no matter what frequecy you operate on.

The ideal position is in the middle of the roof as it provides the best "Ground Plane" for 360 degree signal. If you mount any antenna where the amount of metal is missing from one side. like at the top of a Bull Bar in front of the Bonnet or on the side of your Vehicle Roof then you scew the signal in one direction and reduce it from the other.

If you mount an antenna to one side then you need to create the artificial ground plane, for UHF/VHF you will do better with one of these....

http://www.ebay.com.au/itm/291130643550 ... 1439.l2649

Antennas that state "ground plane independant" is just a sales pitch. When you use very expensive equipment to plot the radiation pattern then you will see what is going wrong. How do I know...???? I have some very expensive equipment, friends that have more and work in the communications business, have done for many years....called Radio Engineers.

I have HF, VHF & UHF Antennas mounted in positions that are not ideal but the best I am going to do as I'm not drilling holes in a roof. The above antenna base I use for VHF/UHF Amateur Radio Communications. Sorry, I don't play with CB much but the principles still apply except you are very limited with the power you can use.

So, if you don't want to drill holes. Mount an Antenna in the best place then it would be on Roof Racks with a nice metal earth below and in the middle of your roof. Make sure all earthing is bonded together.
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Re: UHF antenna placement and "ground"

Post by Chronos » 06 Oct 2014, 2:56 pm

Also front bar mounted antennae give me the s**ts as their constant wobble makes me seasick (car sick). :lol:

As Apollo said centre of the vehicle roof, I've had to compromise and use a magnetic base for my uhf I can take off and lay in the back seat around Sydney and put on the roof out bush.

I use a short who because most of the time I'm in hilly terrain and a massive tall mast wine help in the valleys.

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Re: UHF antenna placement and "ground"

Post by Apollo » 06 Oct 2014, 3:05 pm

Hey Chronos, you should see how "sea sick" my 3.9m HF Antenna makes you feel in front of your eye's when travelling.

Thanks for the reminder, yes, for UHF the ideal is a Magnetic Mount in the centre of the roof if you don't want to drill holes. Just watch out for damage that can happen from flapping antenna cables.

The shorter 1/4 wave ground plane antennas rather than high gain coaxial work much better in hilly country especially using a Repeater Site. The next best would be a Half Wave Stainless for less wind drag and noise. There are a lot of Stainless Steel Antennas made with varying gain that perform very well compared to the Fibreglass monsters that some people seem to like....
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Re: UHF antenna placement and "ground"

Post by BBJ » 06 Oct 2014, 3:14 pm

Waiting for someone to chime in and say "centre of the roof" :roll:

There is always one...
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Re: UHF antenna placement and "ground"

Post by Apollo » 06 Oct 2014, 3:17 pm

BBJ wrote:Waiting for someone to chime in and say "centre of the roof" :roll:

There is always one...


It's already been said..... ;)
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Re: UHF antenna placement and "ground"

Post by Combat_Wombat » 06 Oct 2014, 3:29 pm

Yeah I'm fully aware that I'm not getting the best signal where it's placed but it keeps it out of sight behind the A pillar when driving and only ever gets used in off-road convoys so 100m max range. Thanks for the tips though lads
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Re: UHF antenna placement and "ground"

Post by Warrigul » 06 Oct 2014, 4:02 pm

Combat_Wombat wrote:Yeah I'm fully aware that I'm not getting the best signal where it's placed but it keeps it out of sight behind the A pillar when driving and only ever gets used in off-road convoys so 100m max range. Thanks for the tips though lads


I have always had UHFs in everything I own, rack mounted antennaes on work vehicles(ground independent antennas are better than non). Honestly it doesn't matter where you mount it it will work to some degree and often not working as well as it could is a blessing.

On my current hilkux it is simply on the LHS guard where it was when I bought it.
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Re: UHF antenna placement and "ground"

Post by Bennybigbores » 06 Oct 2014, 7:10 pm

I have mounted hundreds if not thosands in every position imaginable, worked as an auto sparky for 17 years, up high and earthed obviously better but all depends reguarding range as to your unit and the gain of your aerial and that it is compatible with the unit. In hilly country a lower gain aerial will work better than a high gain purely by the shape of the emmitted signal, there's a lot to it if you want to research, but like the last happy 800 customers, put it where you want! Be it bull bar, front guard, head board, the position is neglidgable in common use, the connections and earthing plays a bigger part in my experience, that and matching the gain of the aerial to the unit and landscape to be used in
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Re: UHF antenna placement and "ground"

Post by Warrigul » 06 Oct 2014, 8:18 pm

Bennybigbores wrote:I have mounted hundreds if not thosands in every position imaginable, worked as an auto sparky for 17 years, up high and earthed obviously better but all depends reguarding range as to your unit and the gain of your aerial and that it is compatible with the unit. In hilly country a lower gain aerial will work better than a high gain purely by the shape of the emmitted signal, there's a lot to it if you want to research, but like the last happy 800 customers, put it where you want! Be it bull bar, front guard, head board, the position is neglidgable in common use, the connections and earthing plays a bigger part in my experience, that and matching the gain of the aerial to the unit and landscape to be used in


You are dead right, we generally find that terrain is the biggest limiter here in TAS. I carry two ariels (a short one for hilly country and a proper one for the highway) and usually the short one is just left on more or less permanently.
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Re: UHF antenna placement and "ground"

Post by Apollo » 06 Oct 2014, 9:26 pm

"a short one for hilly country and a proper one for the highway"

You don't have a clue as to what you are talking about.

Explain WHY the difference.

An "auto sparky" does not make an RF Engineer or Technician but simply gives CB'ers what they want to pay for. What a different world it is when you actually want something that works to the best available resources. You guys have a lot to learn as far as radio comunications are concerned.
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Re: UHF antenna placement and "ground"

Post by Warrigul » 06 Oct 2014, 9:47 pm

Apollo wrote:"a short one for hilly country and a proper one for the highway"

You don't have a clue as to what you are talking about.

Explain WHY the difference.

An "auto sparky" does not make an RF Engineer or Technician but simply gives CB'ers what they want to pay for. What a different world it is when you actually want something that works to the best available resources. You guys have a lot to learn as far as radio comunications are concerned.


Look most blokes don't want bullshite, just gear that does the job.

I may not have a clue about the technical side of why it works(and I don't really care) but it works for me in the main areas I frequent and I guess that is what counts. I doubt very much if you have ever had to put UHFs to the uses that I do.

Honestly, I usually give more weight to the tradesmans view rather than an engineers anyday, if it is work proven then that is good enough for me.
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Re: UHF antenna placement and "ground"

Post by Combat_Wombat » 06 Oct 2014, 10:16 pm

Knowing the theory on a topic is always important but at the end of the day there is ground truth...

Just like against all aparent odds my set up worked just fine.

I'm a sparky and out of all the engineers I've dealt with the only ones with a clue at all all did their trade first.
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Re: UHF antenna placement and "ground"

Post by Apollo » 06 Oct 2014, 11:02 pm

My theory / practise comes from "Field Proven Trials" paying for CB (Kids Band) Repeaters that I financed, set up and moved on to more commercial orientated users.

CB...Kid's Band is just that...!!!!

Enjoy playing, Kid's....!!!!

One day you might grow up and see the real world.
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Re: UHF antenna placement and "ground"

Post by Bennybigbores » 07 Oct 2014, 7:16 am

Wow, ill keep using what every other Australian is using a UHF with an aerial mounted where I please and via sheer magic and luck I guess it will work wihout Apollo wisdom,but us kids will play and you can can continue to be an abusive know it all. I'd prefer to play with he KIDS all day, in the real world :shock:
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Re: UHF antenna placement and "ground"

Post by Westy » 07 Oct 2014, 7:39 am

Apollo wrote:My theory / practise comes from "Field Proven Trials" paying for CB (Kids Band) Repeaters that I financed, set up and moved on to more commercial orientated users.

CB...Kid's Band is just that...!!!!

Enjoy playing, Kid's....!!!!

One day you might grow up and see the real world.



Look out here comes Captain Fart Face Ohhhhh Sorry it just Apoollo[/size]


:lol: :lol: :lol:
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Re: UHF antenna placement and "ground"

Post by BBJ » 07 Oct 2014, 9:37 am

Apollo wrote:It's already been said..... ;)


Bah, I had the window open and left the computer for a few hours.

When I got back I did my reply and a bunch had come in without me seeing.

Need to learn to refresh.

"I have HF, VHF & UHF Antennas mounted in positions that are not ideal but the best I am going to do as I'm not drilling holes in a roof."

That's why I said what I said. Everyone says centre of roof is the answer when they don't do it themselves because they know it's not practical. So... Yeah, not useful advice really?

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Re: UHF antenna placement and "ground"

Post by mahna » 07 Oct 2014, 9:40 am

Well the roof is out...

I guess I'm going with regular quarter panel mount to keep it above the bonnet then.
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Re: UHF antenna placement and "ground"

Post by Chronos » 07 Oct 2014, 10:04 am

BBJ wrote:
Apollo wrote:It's already been said..... ;)


Bah, I had the window open and left the computer for a few hours.

When I got back I did my reply and a bunch had come in without me seeing.

Need to learn to refresh.

"I have HF, VHF & UHF Antennas mounted in positions that are not ideal but the best I am going to do as I'm not drilling holes in a roof."

That's why I said what I said. Everyone says centre of roof is the answer when they don't do it themselves because they know it's not practical. So... Yeah, not useful advice really?

2c.


Yeah it's about how you read the op's question

"I've got a UHF radio on the way for the ride, looking for advice on the best mounting position"

There's no argument the center of the roof is the best position as far as signal strength goes but for most it's not practical.

I hate front bar mounts but installers love them because the mountings are usually already there and cable running is easy because it runs through the firewall and there's no fiddling with roof linings or trim

I don't have a front bar so I mount mine on the roof using a magnetic base when I need it, it usually lives on the back seat and works fine there for vehicle convoys

If people put more effort into writing an informative post and answering the op's question instead of taking the opportunity to put sh1t on other forum members these threads would be a great source of reference for others.

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Re: UHF antenna placement and "ground"

Post by Warrigul » 07 Oct 2014, 11:14 am

Combat_Wombat wrote:Knowing the theory on a topic is always important but at the end of the day there is ground truth...

Just like against all aparent odds my set up worked just fine.

I'm a sparky and out of all the engineers I've dealt with the only ones with a clue at all all did their trade first.


Yep, the great majority of Uni engineers are d**kheads.

Engineers were originally weaned with dirty hands and their knowledge was borne out of what worked in practice but somehow it has turned around and it is now okay to say that book learning is a substitute for nouse.
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Re: UHF antenna placement and "ground"

Post by Lorgar » 11 Oct 2014, 10:29 am

Warrigul wrote:Engineers were originally weaned with dirty hands and their knowledge was borne out of what worked in practice but somehow it has turned around and it is now okay to say that book learning is a substitute for nouse.


I work with a guy who is an engineer (now businessman) who worked for ExxonMobil for years doing a lot of their on-paper stuff.

Smart guy, utterly useless at anything that vaguely resembles the "hands on" side of it though.
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Re: UHF antenna placement and "ground"

Post by tom604 » 11 Oct 2014, 9:16 pm

i mounted mine on my roof rack and the short one is 6db or something like that the long is 9 whatevers, short for hills long for flats. just use the short one on mine. sorry i missed the start of this thread it seemed like it was fun :lol: :lol:
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Re: UHF antenna placement and "ground"

Post by Jack V » 12 Oct 2014, 8:29 pm

A radio is an emergency piece of equipment in addition to any other use so why put the antenna where it could be destroyed in a crash or if you hit a cow , roo or deer and I have seen them shot off!

A short stainless whip on the roof will transmit just as well as a longer antenna mounted on the bull bar with a better radiation pattern. It can be taken off quickly when navigating low trees etc. On a magnetic mount it will knock over and usually re clamp if it gets a bad nock as long as some slack is in the cable .

Stick a thin film of rubber under the magnet to stop it scratching the paint job. Seal the cable connections with silicone. In thick bush I would take mine down and stick it on the bonnet , still works about 75% as good.

You can get short Broadband dipole antennas for UHF that are ground independent for a bull bar .
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Re: UHF antenna placement and "ground"

Post by Hugh » 12 Nov 2017, 1:32 pm

WOW Ok flame suit on,Middle of roof is best place of course,i have found in the real world being interested in radio comms and having one in car since my 20s both hf and uhf that where ever you put it ,ground independent or not a good earth is always a great idea.The other is the longer the better,a know everybody says the smaller ants are better for hilly country because of different angle of radiation but I have found the extra gain more than makes up for it.I have had all different types on my car over the years mostly bulbar mounted.All I know is when up in hills deer shooting I'm the always the one relaying messages between different 4wds when they cant hear each other.I run the six foot fiberglass type.Not saying anybody is wrong or right,just my experience.Having said all that running the 6 ft around town not just for parking underground ,but the amount of traffic that comes in to it from Suburbs,ballarat and Bendigo if you have right weather conditions can be a pain but that's what the sq is for.
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Re: UHF antenna placement and "ground"

Post by SendIt » 13 Nov 2017, 12:35 pm

I'll jump into the fire here too.

About mounting a UHF antenna in the middle of the roof...

Someone find me a picture of someone, anyone, who's actually done it.
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Re: UHF antenna placement and "ground"

Post by Hugh » 13 Nov 2017, 2:35 pm

Here you go
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Re: UHF antenna placement and "ground"

Post by SendIt » 13 Nov 2017, 3:53 pm

I'm going to say no.

We're talking about mounting a UHF radio antenna here.

Not accessorizing your car to match your tin foil hat.
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Re: UHF antenna placement and "ground"

Post by Daddybang » 13 Nov 2017, 3:54 pm

Mines on the bull bar and never had a problem with it. I spend A LOT of time on overgrown tracks with trees etc hanging down and getting out to remove one from the roof all the time would just be a pain in the rear!!! :drinks:
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Re: UHF antenna placement and "ground"

Post by on_one_wheel » 13 Nov 2017, 5:56 pm

At the end of the day, a uhf is only good short range communication with the exception of those very limited areas where you can hit a repeater. They shouldn't be relied on for emergencies, that's where satellite phones and HF radios are good.

Most people mount antennas on the bullbar, that's where mine is and it works just fine.
If it were on the roof the tip woukd stand 3.3 meters from the ground, I'd smash that on a tree within the first hour of driving... that's somewhat impractical.

Mounting it on the bar will just make your signal directional.
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