UHF arials

Submitted: Saturday, Feb 25, 2006 at 20:56
ThreadID: 31151 Views:6761 Replies:8 FollowUps:12
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Getting contradictory advice from salespeople on this one! Do those bl...dy big thick spring mounted, 4 feet tall UHF ariels really improve the reception of a modern UHF radio? - or is something a bit more discreet just as good?
And what does dB gain really mean? Some say lower dB gain for flat country , higher for mountains etc? Is all this just old wives tales?
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Reply By: Peter McG (Member, Melbourne) - Saturday, Feb 25, 2006 at 21:29

Saturday, Feb 25, 2006 at 21:29
a mediusize spring mount helps on corrugated roads. i've had a couple of less rugged erials fall apart. And the lower the db the shorter range but better for the hills.Vice versa for flat country.

peter
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AnswerID: 157058

Reply By: Exploder - Saturday, Feb 25, 2006 at 21:37

Saturday, Feb 25, 2006 at 21:37
Lower DB better for Hill’s forest’s ECT, Higher DB for Flat open country, it’s got to do with the Radiating pattern of the Antenna

If you only have one Antenna go for something in the middle like a 6DB or 4.5DB
On a sprig mount.

Just IMO
AnswerID: 157061

Follow Up By: geocacher (djcache) - Saturday, Feb 25, 2006 at 21:57

Saturday, Feb 25, 2006 at 21:57
Please explain your rationale why a lower dB antenna is better in hills & forests.

I'd like to know the disadvantages of a high gain antenna in that situation.

Dave
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FollowupID: 411253

Follow Up By: Exploder - Sunday, Feb 26, 2006 at 03:47

Sunday, Feb 26, 2006 at 03:47
Just looked at the link in the post below made by Paul P; this is basically how I understand it, so it saved me some typing.

If I am wrong in my thinking I will stand corrected, but GME seem to look at it the same.
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FollowupID: 411290

Follow Up By: Mike DiD - Sunday, Feb 26, 2006 at 07:44

Sunday, Feb 26, 2006 at 07:44
A high-gain antenna concentrates the signal in a narrow band - a bit like a light-house shining no light above or below the horizon.

This is great when the vehicle is horizontal and the country is flat. But if you are in a deep valley, most of your signal is aimed at the cliffs, with only a little left to go up and over the cliffs.

The same concept applies to received signals.

Mike
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FollowupID: 411297

Follow Up By: geocacher (djcache) - Sunday, Feb 26, 2006 at 09:42

Sunday, Feb 26, 2006 at 09:42
Hi Exploder & Mike

I'd not actually given a lot of thought of propagation patterns and their affect in those situations.

Funny really because we use propagation patterns to our advantage when you bend a HF whip back to the roof rack to get better short distance performance from the HF sets.

Usual considerations given to propagation patterns involved what the shape and amount of bodywork was going to do in close proximity to the antenna.

Thanks,

Dave
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FollowupID: 411310

Reply By: Member - Paul P (Bris) - Saturday, Feb 25, 2006 at 21:37

Saturday, Feb 25, 2006 at 21:37
Greetings

Go here GME Site- Antennas Explained. I have two that fit on a spring base GME AE4703 for out of town and a AE4701 around town.

Regards

Paul
AnswerID: 157062

Reply By: Member - Ian H (NSW) - Sunday, Feb 26, 2006 at 09:44

Sunday, Feb 26, 2006 at 09:44
Hi, We travelled to the centre and had in our group a Prado with only a centre roof mounted magnetic base 3db aerial. It gave as good a performance as a 6db BADLY MOUNTED aerial on another car's bull bar. I had a 6db Desert Stick on a spring base on the bull bar and got about 15 kms range going out of Alice springs which is obviously flat country. A 3db centre of roof mounted gave great results in the high country where my desert stick is poor. You need the correct aerial for the job. The GME web site or brouchure explains it well for dummies.
AnswerID: 157102

Reply By: Laura B - Sunday, Feb 26, 2006 at 10:25

Sunday, Feb 26, 2006 at 10:25
those big white ones just show the size of your ego and thats about it....i just try to remember quality is better than quantity...we got a tiny little silver thing that is spiraled in the middle - i think its 6db - cos its goes over hills better so when we are out bush doing war wounds to the 80 we get a heap more coverage than the other......our radio/cd player antenna is bigger!!!!

Good luck!!hope thiss helps a little!!

Laura B
AnswerID: 157118

Follow Up By: Member - Paul P (Bris) - Sunday, Feb 26, 2006 at 15:13

Sunday, Feb 26, 2006 at 15:13
Greatings

My little metal one ( as stated in this thread) destroyed itself on corrugated roads hence my new(cost effective fibre glass one.

Also the white/black/grey fibre glass ones are also used for GSM/CDMA antenna ( high gain).

I prefer white. It matches my vehicle colour:-)

Regards

Paul
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FollowupID: 411377

Follow Up By: Wayne (NSW) - Sunday, Feb 26, 2006 at 15:41

Sunday, Feb 26, 2006 at 15:41
Laura B,

The size of the aerial has nothing to do with ego. It is all about trying to get a signal.

The small wire ones are good for around town and roads that are smooth as they don't like to be shaken around. It is only wire and one way to break wire is to bend it back and forth and that is what happens on a rough track.
The big white ones are used in the desert area where the land is rather flat and the higher the aerial the further the range. The aerial works on line of sight. Two high aerials will "see" each other and commutate.

The shorter aerials are good for the areas where there are a lot of low branches. They are of a db that will send a signal over a large area but not much distance.

The aerials are mounted on a large spring base that will allow the aerial to move with out breaking

Wayne.
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FollowupID: 411380

Follow Up By: VK3CAT - Sunday, Feb 26, 2006 at 16:18

Sunday, Feb 26, 2006 at 16:18
One wavelength on UHF CB (477mHz) is approximately 630 millimetres.
The most basic type of antenna is the half wave dipole. With this antenna, 1/4 wave of wire will be connected to the innner wire of the coaxial cable and another 1/4 wave of wire will be connected to the shield. (Note that for simplicity no baluns have been used)
This dipole antenna is used as a common reference antenna - ie gain measured in dbd (decibel gain over a dipole)
The most basic type of mobile antenna will be a 1/4 wave ground plane antenna. This means that the vertical radiating section is approximately 157mm long and the "ground plane" makes up for the missing 1/4 wave.
The radiation pattern of the 1/4 wave antenna will be the highest of most common UHF antennas & makes it perfect for mountain work. (and low trees)

The highest gain antenna commonly used is the 5/8th wave. This concentrates the RF radiation at a lower angle of radiation. Still good in the mountains plus the open country.

The UHF antennas that are longer than a 5/8th wave are known as collinear antennas. These use multiple 1/2 or 5/8 wave sections with 1/4 wave matching sections in order to feed the signal in phase. The advantage of a collinear is higher gain due to a lower angle of radiation. They also are generally ground independant & thus do not require a ground plane.
Also, some of the really long UHF sticks are simply a ground matching section with a 6dbd antenna which provides an elevated feed point. In VHF / UHF, the higher the antenna the better.
UHF communications are not necessarily line of site. Reflection and refraction also play an important part. Thus it can be possible to communicate with a car over the otherside of the hill without being "line of site" This is known as knife edge refraction.
The spring at the base is to avoid the antenna self destructing over corrugations.

Hope that this is of some help.
Cheers Tony.
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FollowupID: 411386

Follow Up By: Laura B - Tuesday, Feb 28, 2006 at 14:49

Tuesday, Feb 28, 2006 at 14:49
where i come from its all about ego and nothing else.......dont need to tell me about what antenna's are used for what.....
laura b
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FollowupID: 411802

Follow Up By: Wayne (NSW) - Tuesday, Feb 28, 2006 at 19:02

Tuesday, Feb 28, 2006 at 19:02
Laura,

I don't know where you come from but like I said it is all about getting a signal.
Because of what I do, I can't afford to have a bit of wire brake and have no commutations and I have found what I am using works for me. I don't drive that much on city roads.

Anyhow I need something bigger for my ego than a aerial, that is why I drive a Troopie.

Wayne

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FollowupID: 411880

Follow Up By: Laura B - Tuesday, Feb 28, 2006 at 20:16

Tuesday, Feb 28, 2006 at 20:16
Wayne,

a troopie will do it!!!! lol !!!!! maybe you could come and give the ute boys a lesson in my town!!

Laura B
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FollowupID: 411898

Reply By: Banjo - Sunday, Feb 26, 2006 at 10:54

Sunday, Feb 26, 2006 at 10:54
apwaddo

If your'e going to travel a lot of corrugated roads then I'd suggest the thicker fibreglass? type section above the spring mounted base.

I had 3 of the thinner stainless steel types shake so much they snapped off, just above where they fit into the thicker piece with the thread. Since going to the other type no problem.

Banjo(WA)
AnswerID: 157123

Follow Up By: Member - Roachie (SA) - Tuesday, Feb 28, 2006 at 20:31

Tuesday, Feb 28, 2006 at 20:31
Banjo, I'm curious.....did the antenna that broke have a spring base? I've been using the same UHF antenna (GME ground-plane independant with a black wire top section, coiled in the middle) for bloody years and have travelled over some mongrel corrogations (eg: Cape York twice) and have never broken or shaken-loose an antenna). I do also have a very short rubber antenna which I screw onto the silver base for around town/local convoy use.
Cheers
Roachie
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FollowupID: 411905

Follow Up By: Banjo - Tuesday, Feb 28, 2006 at 23:22

Tuesday, Feb 28, 2006 at 23:22
Roachie

The top wire bit had the coil as you describe, that was screwed onto a heavier bulbous metal section with a largish coil spring.

Maybe just a coincidence but I broke 3 in total. One on the Gibb River Rd, another going up to Weipa and a third between Weipa and the Cape.

Replaced again at Weipa with the fibreglass type and that has lasted for 2 years.

Banjo

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FollowupID: 411999

Reply By: Leroy - Sunday, Feb 26, 2006 at 15:54

Sunday, Feb 26, 2006 at 15:54
I went for a Polar uhf antenna

http://www.polarelectronicindustries.com/model.php?model_id=465

This is a general purpose antenna and has worked a treat in all conditions.

Leroy
AnswerID: 157157

Reply By: Darian (SA) - Monday, Feb 27, 2006 at 08:49

Monday, Feb 27, 2006 at 08:49
As above, check the GME site re db ratings and the resultant radiating patterns for antennas - quite informative and true ! .... had experience first hand re the wrong pattern - as for types of antennas overall - that seems harder - you get all this odd advice - I think the "broomstick" would be good but unwieldy - I chose an elevated feed GME sprung base - can screw a 150mm and 600mm wire onto that for db changes - mounted on top of the car, my supplier suggests that is their best setup. (min's on the bullbar but) - Don't know how they rate the broomstick.
AnswerID: 157242

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