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Bluest



Member Since: 23 Apr 2016
Location: Lancashire
Posts: 3993

United Kingdom 2007 Defender 110 Puma 2.4 XS CSW Java Black
Calling the CB Gurus
I need some help. I bought a “pre-tuned” antenna as part of a kit with my CB, but the set up has performed terribly. Very short reception distance/transmit range even with line of sight. Just a few hundred metres at best.

I about to completely reinstall the whole lot so are their any top tricks to maximise the performance of the CB. I now know I should get an SWR metre on it and check the antenna is tuned correctly, but what else can I do whilst I’m starting from scratch. 2007 110 TDCi Station Wagon XS
Post #785261 6th Aug 2019 6:13pm
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landy andy



Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5408

2006 Defender 110 Td5 USW Zermatt Silver
NO AERIAL IS PRE-TUNED

That would be my first advice.

Run good quality cable, making sure inner core doesn’t touch out cores, and tune your aerial. I’ve always had to remove a few inches or more.

A well placed aerial is best, so slap in the middle of the roof is ideal. A massive great earth cable to the aerial mount is great. But I’ve never done either of these and I’ve had numerous setups, always with a great range.

I think you will be surprised once you tune it. Thumbs Up Thumbs Up
Post #785294 6th Aug 2019 8:03pm
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jst



Member Since: 14 Jan 2008
Location: Taunton
Posts: 7664

2011 Defender 110 Puma 2.4 USW Stornoway Grey
Get a proper body mount with dedicated earth for it. Cheers

James
110 XS Utility
130 Puma Station wagon/camper (in the making)
90 Puma Hardtop
Post #785299 6th Aug 2019 8:07pm
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Bluest



Member Since: 23 Apr 2016
Location: Lancashire
Posts: 3993

United Kingdom 2007 Defender 110 Puma 2.4 XS CSW Java Black
I've just spent £25 on a new gutter mount, will that be no good? I really don't want to drill any holes in the roof.

This one https://www.thunderpole.co.uk/gutter-mount...t-kit.html 2007 110 TDCi Station Wagon XS
Post #785305 6th Aug 2019 8:16pm
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landy andy



Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5408

2006 Defender 110 Td5 USW Zermatt Silver
I wouldn’t recommend Gutter mounts. They tend to either snap, bend, or just fall off at the sight of a tree, and then you get damage caused by the aerial flailing around, and they also damage the sealer inside the gutter, or paint work of the gutter.
Post #785352 6th Aug 2019 9:35pm
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walfy



Member Since: 29 Aug 2007
Location: Frome
Posts: 2637

 
As said, no arial is pre tuned. It all depends on the ground plane that you have. In the centre of the mass is best which gives the best 360 deg projection of signal.
Lifted from the net, a bit heavy going but explains it correctly

Radio antenna theory

In telecommunication, a ground plane is a flat or nearly flat horizontal conducting surface that serves as part of an antenna, to reflect the radio waves from the other antenna elements. The plane does not necessarily have to be connected to ground. Ground plane shape and size play major roles in determining its radiation characteristics including gain.
For a monopole antenna, the Earth acts as a ground plane to reflect radio waves directed downwards, making them seem to come from an image antenna.

To function as a ground plane, the conducting surface must be at least a quarter of the wavelength (λ/4) of the radio waves in diameter. In lower frequency antennas, such as the mast radiators used for broadcast antennas, the Earth itself (or a body of water such as a salt marsh or ocean) is used as a ground plane. For higher frequency antennas, in the VHF or UHF range, the ground plane can be smaller, and metal disks, screens and wires are used as ground planes. At upper VHF and UHF, the metal skin of a car or aircraft can serve as a ground plane for whip antennas projecting from it. In microstrip antennas and printed monopole antennas an area of copper foil on the opposite side of a printed circuit board serves as a ground plane. The ground plane doesn't have to be a continuous surface. In the ground plane antenna style whip antenna, the "plane" consists of several wires λ/4 long radiating from the base of a quarter-wave whip antenna.

The radio waves from an antenna element that reflect off a ground plane appear to come from a mirror image of the antenna located on the other side of the ground plane. In a monopole antenna, the radiation pattern of the monopole plus the virtual "image antenna" make it appear as a two element center-fed dipole antenna. So a monopole mounted over an ideal ground plane has a radiation pattern identical to a dipole antenna. The feedline from the transmitter or receiver is connected between the bottom end of the monopole element and the ground plane. The ground plane must have good conductivity; any resistance in the ground plane is in series with the antenna, and serves to dissipate power from the transmitter. 110 D250 SE HT
110 USW SOLD
RRE HSE Dynamic Gone, wife killed it
VOLVO XC60 R Dynamic with some toys

Polaris RZR 900XP SOLD
Post #785423 7th Aug 2019 9:20am
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Bluest



Member Since: 23 Apr 2016
Location: Lancashire
Posts: 3993

United Kingdom 2007 Defender 110 Puma 2.4 XS CSW Java Black
It's all a bit much for me that. Would I be better mounting the antenna on the roof bar over the middle of the roof, rather than the gutter? It was on my roof bar previously when I had bad signal strength.

Landy Andy, I understand your points about the vulnerability of the gutter mount to damage but that is not an issue to an extent. I wont be travelling in wooded areas so risk of tree damage is minimal and to an extent the mount is protect by other things around it. 2007 110 TDCi Station Wagon XS
Post #785427 7th Aug 2019 9:31am
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walfy



Member Since: 29 Aug 2007
Location: Frome
Posts: 2637

 
If you use a gutter mount you'll have to run a seperate earth cable due to the mastic in the gutter. I ran a small cable from the arial base to a body screw to ensure a good ground.
If you mount the aerial to the roofbar, you'll have to do the same as you won't have a good ground to the vehicle 110 D250 SE HT
110 USW SOLD
RRE HSE Dynamic Gone, wife killed it
VOLVO XC60 R Dynamic with some toys

Polaris RZR 900XP SOLD
Post #785428 7th Aug 2019 9:36am
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Bluest



Member Since: 23 Apr 2016
Location: Lancashire
Posts: 3993

United Kingdom 2007 Defender 110 Puma 2.4 XS CSW Java Black
Just to be clear, the antenna mount itself needs to be grounded to the chassis of car? I thought it was grounded somehow via the co-ax cable. 2007 110 TDCi Station Wagon XS
Post #785429 7th Aug 2019 9:45am
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Bluest



Member Since: 23 Apr 2016
Location: Lancashire
Posts: 3993

United Kingdom 2007 Defender 110 Puma 2.4 XS CSW Java Black
landy andy wrote:
NO AERIAL IS PRE-TUNED

That would be my first advice.

Run good quality cable, making sure inner core doesn’t touch out cores, and tune your aerial. I’ve always had to remove a few inches or more.

A well placed aerial is best, so slap in the middle of the roof is ideal. A massive great earth cable to the aerial mount is great. But I’ve never done either of these and I’ve had numerous setups, always with a great range.

I think you will be surprised once you tune it. Thumbs Up Thumbs Up


Sorry, I somehow missed this comment and jumped straight to JST's. I will ensure the mount is earthed to the car, can do that easily enough and get the antenna tuned with an SWR meter (my friend has one). 2007 110 TDCi Station Wagon XS
Post #785430 7th Aug 2019 9:47am
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walfy



Member Since: 29 Aug 2007
Location: Frome
Posts: 2637

 
If you rely on the coax to ground it you are relying on a long run of cable and then the head unit to have adequate grounding. It makes much more sense to ground the aerial mount. This way you can be sure that you have a good ground.
But I'm basing my thought process on over 20yrs as a military communicator where we ground everything due to the distances we talk over. 110 D250 SE HT
110 USW SOLD
RRE HSE Dynamic Gone, wife killed it
VOLVO XC60 R Dynamic with some toys

Polaris RZR 900XP SOLD
Post #785431 7th Aug 2019 9:47am
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Bluest



Member Since: 23 Apr 2016
Location: Lancashire
Posts: 3993

United Kingdom 2007 Defender 110 Puma 2.4 XS CSW Java Black
Thanks Walfy, it's be easy enough to run an earth cable down the snorkel and ground it on the bulkhead somewhere. 2007 110 TDCi Station Wagon XS
Post #785432 7th Aug 2019 9:50am
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geobloke



Member Since: 06 Nov 2012
Location: Nottinghamshire
Posts: 4348

United Kingdom 
walfy wrote:
As said, no arial is pre tuned. It all depends on the ground plane that you have. In the centre of the mass is best which gives the best 360 deg projection of signal.
Lifted from the net, a bit heavy going but explains it correctly

Radio antenna theory

In telecommunication, a ground plane is a flat or nearly flat horizontal conducting surface that serves as part of an antenna, to reflect the radio waves from the other antenna elements. The plane does not necessarily have to be connected to ground. Ground plane shape and size play major roles in determining its radiation characteristics including gain.
For a monopole antenna, the Earth acts as a ground plane to reflect radio waves directed downwards, making them seem to come from an image antenna.

To function as a ground plane, the conducting surface must be at least a quarter of the wavelength (λ/4) of the radio waves in diameter. In lower frequency antennas, such as the mast radiators used for broadcast antennas, the Earth itself (or a body of water such as a salt marsh or ocean) is used as a ground plane. For higher frequency antennas, in the VHF or UHF range, the ground plane can be smaller, and metal disks, screens and wires are used as ground planes. At upper VHF and UHF, the metal skin of a car or aircraft can serve as a ground plane for whip antennas projecting from it. In microstrip antennas and printed monopole antennas an area of copper foil on the opposite side of a printed circuit board serves as a ground plane. The ground plane doesn't have to be a continuous surface. In the ground plane antenna style whip antenna, the "plane" consists of several wires λ/4 long radiating from the base of a quarter-wave whip antenna.

The radio waves from an antenna element that reflect off a ground plane appear to come from a mirror image of the antenna located on the other side of the ground plane. In a monopole antenna, the radiation pattern of the monopole plus the virtual "image antenna" make it appear as a two element center-fed dipole antenna. So a monopole mounted over an ideal ground plane has a radiation pattern identical to a dipole antenna. The feedline from the transmitter or receiver is connected between the bottom end of the monopole element and the ground plane. The ground plane must have good conductivity; any resistance in the ground plane is in series with the antenna, and serves to dissipate power from the transmitter.



Just to add to the super explanation above, here is an image to illustrate how positioning of an aerial and the ground plane can effect the signal strength and coverage;




And how aerials with different gain levels and topography affect your operational range.




I cannot remember where I found these, but have had them saved as reference for ages...
Post #785437 7th Aug 2019 10:21am
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landy andy



Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5408

2006 Defender 110 Td5 USW Zermatt Silver
I would start by keeping your setup. Aerial on roof bar and tune it. Test it. Then run a temporary earth cable to the base and test again. I bet you won’t see much difference. On my double cab I just had a temporary removable mount. I tried the same test and concluded that the earth to it did nothing. Being high and in the centre of the vehicle was plenty good.
Post #785483 7th Aug 2019 2:03pm
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Bluest



Member Since: 23 Apr 2016
Location: Lancashire
Posts: 3993

United Kingdom 2007 Defender 110 Puma 2.4 XS CSW Java Black
Antenna is no longer on the bars, as I got some new bars and the mount I had wasn't suitable for the new ones. Hence the switch to a gutter mount, which I was going to put just above the drivers' door so I can hide the antenna cable behind the snorkel, run it into the engine bay and through the bulkhead into the cabin.

When you say run an earth to the base, what do mean by the base? 2007 110 TDCi Station Wagon XS
Post #785484 7th Aug 2019 2:22pm
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