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| Placement of UHF antenna http://auszookers.com/forum/viewtopic.php?f=5&t=26038 |
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| Author: | Robbo86 [ Thu Sep 22, 2011 5:28 am ] |
| Post subject: | Placement of UHF antenna |
Hey Everyone, I just bought a GME 3100 compact cb for my sierra. It was installed easily and so was the antenna, which i mounted onto the aluminium bull bar. My question is though...Would it have been better to mount the antenna on my suzies front fender on the little flat section right next to the front of the bonnet, almost directly above the headlight itself (If that makes sense). Its just that im not sure its performing as good as it could be, or whether i have done anything wrong during install. Would it act as a better receiver/transmitter in that position? If anyone could give me some pointers that would be very much appreciated as im not very radio savvy. |
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| Author: | royce [ Thu Sep 22, 2011 5:47 am ] |
| Post subject: | Re: Placement of UHF antenna |
I had mine there way back on my 1 litre, if its as high on your bar youll probably not notice any difference to where it is now |
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| Author: | TheOtherLeft [ Thu Sep 22, 2011 5:47 am ] |
| Post subject: | Re: Placement of UHF antenna |
The best place for an antenna is in the middle of the roof, or even on a roofrack using a ground independent antenna. Nice and high clear of any body work. I can't see the value why people mount it near the spare wheel right next to the back door. From my understanding on where you have it mounted at the moment, I can't see it making much difference between the bullbar or fender mount above the headlight, assuming they are at the same level. |
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| Author: | Robbo86 [ Thu Sep 22, 2011 5:54 am ] |
| Post subject: | Re: Placement of UHF antenna |
i dont know if its a problem but i have a fiberglass hardtop and i would have to be sure where it went, i dont want to have a series of holes in it haha. i also have a roof basket, not sure if that changes anything. also, the distance between where it is now and as a maybe on the fender would be about 20cm taking it to just above the roof line. |
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| Author: | Robbo86 [ Thu Sep 22, 2011 6:03 am ] |
| Post subject: | Re: Placement of UHF antenna |
Would buying a longer antenna make it a better unit or does that have nothing to do with it? |
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| Author: | Ben_Sierra [ Thu Sep 22, 2011 6:07 am ] |
| Post subject: | Re: Placement of UHF antenna |
Antenna theory is complex. The length of an antenna often has more to do with frequency than gain. Also, antennas acheive gain by focusing the radiation. A higher gain means a narrower beamwidth. On flat terrain a high gain antenna will give you a long range, but on hilly terrain a lower gain antenna will be better, as shown in the image below. 
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| Author: | TheOtherLeft [ Thu Sep 22, 2011 6:10 am ] |
| Post subject: | Re: Placement of UHF antenna |
Robbo86 wrote: i dont know if its a problem but i have a fiberglass hardtop and i would have to be sure where it went, i dont want to have a series of holes in it haha. i also have a roof basket, not sure if that changes anything. also, the distance between where it is now and as a maybe on the fender would be about 20cm taking it to just above the roof line.
I would place it at the edge of the roof basket so it's up high but you can still use the basket. Be aware though of carparks etc as you probably won't fit. You could always fab a hinge so you can stow the antenna when in carparks. |
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| Author: | Robbo86 [ Thu Sep 22, 2011 6:10 am ] |
| Post subject: | Re: Placement of UHF antenna |
ok then, that gives me a bit of an understanding. The antenna i got from arb was a 6db gain and came with the elevated feed base aswell. so does that mean that in a suburban area that as an antenna mine wouldnt be too good its more for distance like your said, on flat terrain? |
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| Author: | Robbo86 [ Thu Sep 22, 2011 6:12 am ] |
| Post subject: | Re: Placement of UHF antenna |
oh ok cool thanks TheOtherLeft. A hinge set up might not be a bad idea at all if i end up moving it to the basket. cheers |
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| Author: | Ben_Sierra [ Thu Sep 22, 2011 6:22 am ] |
| Post subject: | Re: Placement of UHF antenna |
Robbo86 wrote: ok then, that gives me a bit of an understanding. The antenna i got from arb was a 6db gain and came with the elevated feed base aswell. so does that mean that in a suburban area that as an antenna mine wouldnt be too good its more for distance like your said, on flat terrain?
Nothing is that great in suburban areas, really, with all of the buildings in the way... 3dB would probably by virtue of the wider beamwidth, give you marginally better performance, but in an urban area there are all sorts of factors to consider, such as reflections and multipath fading, diffraction, etc etc which can't be fixed just by changing antenna gain... Without complex modelling of the buildings and terrain and the routes you drive, etc etc its impossible to say with 100% accuracy which antenna is the best for you. Do you have the part number for the antenna you have? |
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| Author: | Robbo86 [ Thu Sep 22, 2011 6:31 am ] |
| Post subject: | Re: Placement of UHF antenna |
wow sounds like my perception of radio waves is missing quite a number of factors haha. yeah i have a part number its a GME AE4018 but as the whole set up with the elevated feed base and spring is AE4018K1. |
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| Author: | Ben_Sierra [ Thu Sep 22, 2011 6:36 am ] |
| Post subject: | Re: Placement of UHF antenna |
Ok. The antenna you have is a 477MHz (which is the right frequency) 6.6dBi antenna. It is ground dependant. So it needs a good ground plane to work effectively. So a bull bar or fender mount is not ideal for this antenna. The roof would be a more effective mounting place. |
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| Author: | Robbo86 [ Thu Sep 22, 2011 6:44 am ] |
| Post subject: | Re: Placement of UHF antenna |
does ground dependant mean that it requires a metal surface mount to receive signal properly. also, what does the elevated feed base do |
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| Author: | Ben_Sierra [ Thu Sep 22, 2011 6:51 am ] |
| Post subject: | Re: Placement of UHF antenna |
Ground dependant means that it needs a ground plane (metal) below it to work effectively. Interestingly, on further research, the standard antenna is listed as ground dependant, but the one with the elevated feed base is listed as ground independant, so you should be ok... |
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| Author: | Robbo86 [ Thu Sep 22, 2011 6:53 am ] |
| Post subject: | Re: Placement of UHF antenna |
ah ok then. so does it coming in a kit with the elevated base mean that its not required to be on a conductive metal surface? is that the purpose of those bases? |
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| Author: | Robbo86 [ Thu Sep 22, 2011 7:06 am ] |
| Post subject: | Re: Placement of UHF antenna |
so if i possibly change the location to the roof somewhere, performance may be improved or i could just leave it where it is and accept it as thats it and maybe get a low gain antenna too screw onto the base for urban and/or hilly locations. Would that seem like a plausable solution? |
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| Author: | Mike57 [ Thu Sep 22, 2011 9:27 am ] |
| Post subject: | Re: Placement of UHF antenna |
While the ideal place might be in the middle of the metal roof in reallity if you are only talking to other vehicles within a few km or less then the mounting location is not going to matter much. Sure by mounting on the top you have a good omni-directional signal and by mounting it on the front or back of the car you will make it slightly directional but unless you are trying to work really long distances and squeeze the last bit of performance out of it you won't notice the difference. One reason for mounting it towards the back of the car by the way is to get it away from the engine electrics although I agree that attached the the spare tyre mount is less than optimal but then again it will work OK. |
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| Author: | Robbo86 [ Thu Sep 22, 2011 12:08 pm ] |
| Post subject: | Re: Placement of UHF antenna |
ok then cool, thanks everyone for your help. i guess ill try some experimenting this weekend. cheers |
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| Author: | shep [ Thu Sep 22, 2011 12:16 pm ] |
| Post subject: | Re: Placement of UHF antenna |
on the shitbox limmo we just had a 30cm 4.5db whip antenna mounted on the roof which was fiberglass and it worked very well. |
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| Author: | Samurai81 [ Thu Sep 22, 2011 6:43 pm ] |
| Post subject: | Re: Placement of UHF antenna |
While you'll get a great signal in and out on with the aerial on the roof the problem over here is we're often driving through virtual tree tunnels and anything that sticks above the body gets scraped off. Aerial mounting then becomes a compromise. |
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| Author: | shep [ Thu Sep 22, 2011 8:52 pm ] |
| Post subject: | Re: Placement of UHF antenna |
Samurai81 wrote: While you'll get a great signal in and out on with the aerial on the roof the problem over here is we're often driving through virtual tree tunnels and anything that sticks above the body gets scraped off. Aerial mounting then becomes a compromise.
thats why i have a 30cm rubber whip antenna 
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| Author: | Robbo86 [ Fri Sep 23, 2011 9:03 am ] |
| Post subject: | Re: Placement of UHF antenna |
yeah i was thinking too that i may have been sold a too high of a decibel antenna for what i want. seems like 4.5db is pretty good all round and mine is 6.6 |
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| Author: | Robbo86 [ Fri Sep 23, 2011 9:27 am ] |
| Post subject: | Re: Placement of UHF antenna |
would it make any difference to receiver strength moving the antenna from the aluminium bull bar to the suzie at the front of the bonnet? |
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| Author: | bazook [ Fri Sep 23, 2011 12:44 pm ] |
| Post subject: | Re: Placement of UHF antenna |
could you run a splitter and run both 9 and 6 db to get both gains or would they interfer or cancel each other out sort of thing |
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| Author: | Mike57 [ Fri Sep 23, 2011 1:19 pm ] |
| Post subject: | Re: Placement of UHF antenna |
You will have losses associated with the splitter but more importantly the matching will be a problem and there is a good chance of the signals will cancel out unless the phasing is correct. So all round it would not be a good idea to have two antennas. Two antennas can be used to enhance receiver performance when set up correctly but when transmitting there are lots of complications. It is not straightforward. |
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| Author: | bazook [ Fri Sep 23, 2011 2:22 pm ] |
| Post subject: | Re: Placement of UHF antenna |
cool no worries 
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| Author: | laurie [ Fri Sep 23, 2011 8:56 pm ] |
| Post subject: | Re: Placement of UHF antenna |
shep wrote: Samurai81 wrote: While you'll get a great signal in and out on with the aerial on the roof the problem over here is we're often driving through virtual tree tunnels and anything that sticks above the body gets scraped off. Aerial mounting then becomes a compromise. thats why i have a 30cm rubber whip antenna i had my 6db fibreglass whip stuck in a hole in the roof an orange tree killed it. i now have a 30cm 3db rubber whip about 30cm back from the windscreen in a new hole i found 
it works great. minimal interference with my roof racks. no problem with underground carparks and was cheap. |
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