UHF Antennae

Submitted: Friday, Aug 29, 2003 at 09:47

ThreadID: 6907 Views:1802 Replies:7 FollowUps:4

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Caren

Can anyone tell me what is the best sort of UHF antennae to get for coverage and reliability. My current antennae is quite small.

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Reply By: Will - Friday, Aug 29, 2003 at 10:06

Friday, Aug 29, 2003 at 10:06

There are so many to choose from and it depends on the type of mount you have and the application, also what sort of country/terrain you will most likely use it in. Low Db antennas are better for hilly terrain where there are lots of obstacles to the signal, high Db antennas better for flat country where you can push the signal out further. I have a GME AE409 antenna which is a selectable 6db or 9db antenna and is also ground plane independant. These are widely used antennas, popular in the farming community. I recommend www.prestigecom.net.au, it'll be hard to beat their prices. Hope that helps!
Will

AnswerID: 29542

Reply By: Member - Nigel (QLD) - Friday, Aug 29, 2003 at 18:58

Friday, Aug 29, 2003 at 18:58

I've never tried it, but been told by those who know, that a 1/4 mounted in the centre of your roof will do very well.

If your like most, and don't want to put a hole in your roof then a POLAR brand elevated feed is the best I've found. It's a fibreglass 6dB whip on a metal base about 20 cm long - overall length is about a metre.

Get the one that comes with the oversized spring - and it will be virtually unbreakable.

AnswerID: 29585

Reply By: Eric - Friday, Aug 29, 2003 at 21:44

Friday, Aug 29, 2003 at 21:44

Caren.
The type of antenna is less important than the way it is mounted. If you run you coax through the engine compartment and on to the bull bar you will get poor performance when driving. As nigel says the best spot is the roof centre because the antenna will pick up less of the engine interferance. The second best is a bracket of the spare wheel mount, keep the base of the antenna at roof hight and the coax short. The story about diferent antenna for hilly and flat ground is a myth. Eric.

AnswerID: 29607

Follow Up By: Mad Dog Morgan (Vic) - Friday, Aug 29, 2003 at 23:02

Friday, Aug 29, 2003 at 23:02

Different antennas have different angles of radiation. The higher gain antenna has a flatter main lobe than its lower gain cousin, it hugs the ground doesn't have high angled sky waves. In a polar plot the main lobe extends further therefore the communciations distance is further than an antenna with lower gain which has more energy directed skywards. So, if you're at the bottom of a gully and want your signal to scatter over the top of a high ridge then a low gain antenna is the go. If you're at the top of a ridge and want to communciate down to the gully then a high gain antenna is the go. Well that's the theory I learnt 20yrs ago when studying for my ham ticket. One thing for sure is that antenna radiation patterns are no myth and can be influenced by a number of factors.Hooroo

FollowupID: 20727

Follow Up By: Dennis (Brisbane) - Saturday, Aug 30, 2003 at 00:03

Saturday, Aug 30, 2003 at 00:03

mmmmmmmmmmmmmm, a myth huh?

Not so sure anyone who knows about antenna theory will agree with that one.

Put simply, a low db antenna (3 db) will have a radiating area shaped like an egg eminating from the antenna, so the bubble of reception is almost as tall as it is long.

A mid range (6 db) antenna will have a shape that is flatter but reaches further distance, still has fair height though.

A long range (9 or 12 db) antenna has a very flat but long reception area.

Have a look at the pictures on this page to get an idea of the shapes and the termsalthough it is a boating page the theory is the same.

FollowupID: 20735

Follow Up By: Will - Saturday, Aug 30, 2003 at 02:08

Saturday, Aug 30, 2003 at 02:08

I'll stick with what I said, it's no myth.
Will.

FollowupID: 20737

Follow Up By: Member - Nigel (QLD) - Saturday, Aug 30, 2003 at 10:58

Saturday, Aug 30, 2003 at 10:58

Antenna Gain isn't a myth - there are just more factors involved than people understand, so the results can't be as easily predicted as people would like.

FollowupID: 20747

Reply By: Bob Y. - Qld - Saturday, Aug 30, 2003 at 11:33

Saturday, Aug 30, 2003 at 11:33

Caren,

Regardless of the theory mentioned above, for economy, performance and size, you can't beat the POLAR mentioned by Nigel. They will also work on the bullbar, but not as good as mounted somewhere a bit higher. like roof rack etc.
You can also remove the fibreglass antenna, and replace it with a 150mm unity gain, for use in town, where there might be low awnings, servo's etc. RFI and BENELEC make similar aerials, of similar gain.

We made up a bracket to mount these, at the top of Toyota snorkel, on HZJ75-78's.

Enjoy your trip, Hooroo...

AnswerID: 29628

Reply By: Eric - Sunday, Aug 31, 2003 at 21:00

Sunday, Aug 31, 2003 at 21:00

Caren and others.
The comments about gian and polar paterns are all true and correct, but the diference in paterns is not significant. The limiting factor on cb performance is the signal to niose ratio, there is plenty of power in the signal, the transmitters in satellites are about the same power and much more distant. The reason a higher gain antenna does not make any diference is that the noise is also increased, to put it in simple terms if recieving the signal is like finding a needle in a hay stack, then having a bigger antenna makes the hay stack bigger by the same amount as it increases the signal. The best performance is gianed by placing the antenna in a shadow from the niose i.e. the motor so a small antenna is more in the shadow than a larger one on the roof. Eric.

AnswerID: 29735

Reply By: Frankenstein - Wednesday, Sep 03, 2003 at 21:36

Wednesday, Sep 03, 2003 at 21:36

I started with a fibreglass whip but broke it in the bush, so I then purchased a stainless steel antenna with the spring in the middle (purchased from Dick Smiths with a 5 year warranty) - It lasted all of about 7Km's on the Gibb River Road before it snapped off from the corrugations just above the screw on base.
I now carry two One fibreglass, 1 s-steel and change it for the prevailing conditions.

It doesn't matter what the performance is, any antenna is useless if its broken.

Cheers
Alan

AnswerID: 30040