Becks Bear

Becks Bear

Active Member
hi
moonraker cb installed, working ok
new aerial cable and stinger 4ft aerial connected via a roof mounting bracket on the roof of the landy, have taken a earth lead from the earth to the bolt on the roof mounting inside on the roof, is this earth ok:confused: :confused: :confused:

heres the problem, having tested the unit i appear only to get reception up to one mile from another unit on flat ground no hills etc

have borrowed a POWER SWR meter and when i take the readings the SWR out put is about 2.7 nearly in the red, it appears i need to shorthen the aerial, do i JUST cut the tip of the top of the aerial:confused: :confused: :confused: :confused:
 
Becks Bear said:
hi
moonraker cb installed, working ok
new aerial cable and stinger 4ft aerial connected via a roof mounting bracket on the roof of the landy, have taken a earth lead from the earth to the bolt on the roof mounting inside on the roof, is this earth ok:confused: :confused: :confused:

heres the problem, having tested the unit i appear only to get reception up to one mile from another unit on flat ground no hills etc

have borrowed a POWER SWR meter and when i take the readings the SWR out put is about 2.7 nearly in the red, it appears i need to shorthen the aerial, do i JUST cut the tip of the top of the aerial:confused: :confused: :confused: :confused:
Click to expand...

Usually there's an allen bolt near the bottom which will allow you to move the aerial up or down.
 
redhand
many thanks
yes there is an allen bolt. just move it down on this:confused: :confused: can i cut a bit of the bootom of the aerial if the readings still needs to come down:confused: :confused: my mate tells me i should NOT have the roof aerial earthed is this correct:confused: or is he talking out of his arse:confused: :confused:

the SWR meter i have borrowed only has two meter indicators, one for power and one for swr with a control knob in the middle with settings 1 to 10:confused: no other markings on the meter
 
the roof of your deepender is aluminium, which is a poor ground-plane for an antenna. fit a piece of sheet steel about 12" square under the base of the aerial and below the roof of the vehicle. use the aerial mounting nut to hold it in place, so that there is good contact between the aerial and the sheet. then run a thick wire from the steel sheet to a good earth point on the chassis.
do this before checking / adjusting your SWR.

(a biscuit tin lid will do, as long as it is steel - check with a magnet).
 
Treworgey 90 said:
the roof of your deepender is aluminium, which is a poor ground-plane for an antenna.

(a biscuit tin lid will do, as long as it is steel - check with a magnet).
Click to expand...

Really? Aluminium is a poor metal for a ground plane?
Please explain. I want to hear the science behind your assertion.

In my humble opinion, aluminium sheet is about as good as it gets for ground planes, and aluminium rods are as good as it gets for long antennas, so where you are getting that idea from is interesting to say the least.

My old Landy has an aluminium rear body, with a cb antenna fitted to it, and the SWR is as close to 1:1 as one ever sees.

CharlesY
 
Its true, aliminuim maks a bad ground plane, if still no joy with the earth, go on to 4x4cb.com and you can buy an artificial ground plane, dropped my SWR to 0.3
 
Well, I don't agree with that about aluminium.

I have never had any bother at all fitting aerials to aluminium panels.

CharlesY
 
Here's the gen:

Aluminium as a metal, as in sheet metal in LandRovers and Aston Martins is the THIRD BEST material that exists for use as a ground plane to any antenna.

The best is SILVER, next best is COPPER, then ALUMINIUM, and way down the list are the various steels and ferrous alloys.

So, aluminium is fine, BUT ..... it oxidises rapidly on exposure to air, and it is very soft. Neither of those is good in this context.

Aluminium oxide is a non-conductor of electricity - it is a strong di-electric. For this reason it is difficult to connect an aerial to aluminium in such a way that a good electrical connection is made AND MAINTAINED long term.

You could bolt or rivet a steel or copper plate below the aluminium panel, but that brings a serious risk of "differential metals electrolytic corrosion", by having a sandwich of two unlike metals, bolted together with possibly another metal or alloy, with dampness getting in between. It sets up like a battery and eats the metals away leaving nasty crusty salts - corrosion.

Use the aluminium panels to mount your antenna through - no problem - but make sure you clean the aluminium properly (dry stainless-steel pot-scourer is good) and smear Vaseline, or even better that conducting battery terminal grease all over the clamping areas.

It will work fine for years and years. Just check it for tightness once in a while as it may work loose by digging-in to the soft aluminium.

CharlesY
 
CharlesY said:
Here's the gen:

Aluminium as a metal, as in sheet metal in LandRovers and Aston Martins is the THIRD BEST material that exists for use as a ground plane to any antenna.

The best is SILVER, next best is COPPER, then ALUMINIUM, and way down the list are the various steels and ferrous alloys.
Click to expand...

D'yer know, in between being a grumpy bastid yer do speak some sense! ;)
 
didn't use the steel tin as was suggested, instead reconnected the system as it was after re-checking all connections, reconnected the earth to the base of the securing bolt on the aerial it now appears that the SWR has indeed dropped from the first reading.

have found somebody who is a serious radio ham, he will check the unit next week.:) :) :)

many thanks for all the comments, it really is good to talk, as not everyone knows everything, and the combined pool of knowledge on this site is excellent:D :D :D :D :D :D :D
 
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