UHF Antenna location

[Ranga]

I spotted a forum member's antenna the other day located in the middle of his Defender roof. Anyone care to comment of the pros/cons of antenna location?

[ADMIRAL]

I spotted a forum member's antenna the other day located in the middle of his Defender roof. Anyone care to comment of the pros/cons of antenna location?

I asked a similar question some time ago. It would come up with a search. I will try to relate my understanding from that query. If the antenna was not ground plane independant ( and most on the market now are ) the centre of the roof is a good spot, and provides an ideal reflector, and good height. The same applies for a ground plane independant antenna, but in reality it doesn't need that big flat roof as a reflector, just the height.

One potential consideration for a roof mounted antenna, is the type of construction. Probably not a good idea to have a super rigid antenna up so high, if your trekking includes scrub work.

I am currently looking at mounting my antenna on a pedestal on the spare wheel carrier. ( very much like the current VHF setups ) It was to have been mounted on the roofrack, but this became inconvenient for loading, and now I also intend to remove the rack between trips.

The current thinking seems to be, use a ground plane independant antenna, and get it as high as practicable.

[waynep]

Yes, everything said above is correct.
At UHF no matter what aerial you have, the higher you can get, and clear of other vertical metal, the better. But it's always a compromise for those that go into forested areas.

[VladTepes]

Ranga you could have just asked me, and i would have said exactly the above !

[THE BOOGER]

mount it on the roof with a good spring base and trees and shrubs are not a big problem but car parks are still a pain you smash all their fluros:twisted:

[JDNSW]

Centre of the roof is the ideal position from the communication point of view. But is the worst possible position from the point of view of overhanging trees and carparks, carports, garages etc.

Balance these pros and cons and make your own decision. For what it is worth, both my Landrovers have them on the bullbar. Not ideal, but won't get overhanging trees etc and you can see what they are hitting.

John

[miky]

Centre of the roof is the ideal position from the communication point of view. But is the worst possible position from the point of view of overhanging trees and carparks, carports, garages etc.

Balance these pros and cons and make your own decision. For what it is worth, both my Landrovers have them on the bullbar. Not ideal, but won't get overhanging trees etc and you can see what they are hitting.

John


x2


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[rusty05]

x3

And a high gain antenna is best out in the open areas as it propagates the signal out horizontal more than up.
So high gain like 12db is good for open area etc, but not so great in hilly areas. a smaller gain antenna of <6 db is better suited to hilly terrain. So if u have spare $$, and spend time in each terrain, u would benefit from swapping them around.
(If u could be bothered)

[twodoors]

Seen a few Disco's with a mount for the aerial constructed/located on the rear wheel carrier. Last one looked like the rfi cd9000 6db....
Any thoughts on this position...
James

[ADMIRAL]

Mine is now mounted on the spare wheel carrier. ( version 3 ) I use a small floppy around town on an interchangeable GME screw base. I change over to a longer spring mounted antenna when out on trips. So far it works fine, but the 3 versions have gone higher and higher. The base is now about level with the roofrack, as I found the verticals on the roofrack were interfering with the signal going forward. It looks ok and causes no issue with vision rearward. The antenna lead run in length is a little too long for my liking, but I cannot see anyway to shorten it.

[buddha D2]

Seen a few Disco's with a mount for the aerial constructed/located on the rear wheel carrier. Last one looked like the rfi cd9000 6db....
Any thoughts on this position...
James

I had my UHF and broomstick phone antennas mounted on rear wheel carrier of D2 until I recently installed my ARB bar, which is here the antennas now reside. I would say I am now getting far superior reception than the rear mounted position. RFI hi-gain type UHF antenna.

Gags

[ADMIRAL]

I had my UHF and broomstick phone antennas mounted on rear wheel carrier of D2 until I recently installed my ARB bar, which is here the antennas now reside. I would say I am now getting far superior reception than the rear mounted position. RFI hi-gain type UHF antenna.

Gags

How high was the antenna base mounted on your wheel carrier ?

[MICHELINXMS244]

My 94 LSE came with a glass mount front windscreen analogue mobile phone 800Mhz aerial and cabling so I simply had it retuned to 477Mhz. It works fine for UHF CB. A unity gain whip for UHF CB is tiny. Gutter mount is best if you're unwilling to drill the roof. No chance of scraping the car park fluros. Massive bar mounted UHF CB high gain whips are more for plumage than practical purposes. Granted, they will certainly get you respect at the Deni ute muster... especially the good old twin trucker style...Any decent track will shake them to bits. That's if the trees don't trim 'em first...

[dominicbeirne]

When I got my UHF I ordered a bracket from this bloke in Mittagong NSW. It arrived 2 days later and works perfectly for me, predominantly highway and beach work but some bush bashing stuff in western and central Qld also.

Cheers

Dom

[Duck's Guts]

x3

And a high gain antenna is best out in the open areas as it propagates the signal out horizontal more than up.
So high gain like 12db is good for open area etc, but not so great in hilly areas. a smaller gain antenna of <6 db is better suited to hilly terrain. So if u have spare $$, and spend time in each terrain, u would benefit from swapping them around.
(If u could be bothered)

This is probably a dumb question...but...

Could you install both a 12db & a <6db via a three way splitter off the coax, or does this sap the transmit 'power'?

[rusty05]

This is probably a dumb question...but...

Could you install both a 12db & a <6db via a three way splitter off the coax, or does this sap the transmit 'power'?

You could, but dont.
theory is 3db loss every time u split (which is half ), in reality it is a bit more around 3.5 db loss
Once u start to use 2, u then need to consider the distance between them( in multiples of 1/4 wavelengths), they also then change their pattern. It gets complicated and is best left for base stations which need signal to go in the same direction every time all the time, unlike a car.

[Sidewinder76]

When I got my UHF I ordered a bracket from this bloke in Mittagong NSW. It arrived 2 days later and works perfectly for me, predominantly highway and beach work but some bush bashing stuff in western and central Qld also.

Cheers

Dom


Do you know where I can get one of these for a P38?

Cheers.