Can't get SWR down below 3?

I have recently purchased a Cobra 29LX EU
And Set it all up but I cannot get the SWR to a level I can actually use it.

I have put a 16amp wire between the base of the mount and the chassis and I can get continuity from the chassis to the base of the mount. I have continuity from the pin in the lead on the cb end to the antenna so can't see an issue there. I have checked the mount separately and no continuity from top to bottom as I would expect and there is continuity from the hole where the pin goes in to the top of the mount.

I am set on UK and cannot get below 3 on any channels.

Any ideas?

I had a snag getting my swr down from 10 until i used a spanner to screw the aerial into the mount fully

I'm not an expert on electronics/radio waves or cbs, so can only share information I was given when I was setting up my own cb. It was concerning running an extra earth cable from the mount to earth. Whilst that seemed to be the received wisdom, a number of posters suggested that the extra wire turned the aerial into a dipole and adversely affected the SWR reading. You could try for an SWR reading without the extra earth lead.

You DO NOT need an extra earth the antenna mount is more than capable of using the car as a ground without the addition of an extra wire. A few Microns of paint won't affect the tranmission of radio wave.

As said adding an extra wire can change the lenght of the Antenna.

So remove the cable.

Tell us
what Motor
What Antenna
What type of Mount.
How is it wired. direct to battery thru an ignition swtiched source ??

what have you mounted the antenna to. have you checked for continuity between the inner core and outer sheath of the Coax Cable. ??

110 defender
Wilson beehive mount
Orbitor HD Antenna

Unit is wired direct to battery.

The lead seems ok, no continuity between the pin and the outer sheath.

Mounted on top of front wing 2' in front of windscreen.

I will lose the extra cable tomorrow and see if that helps. Richard at Thunderpole said I would need the extra earth as it was a defender. New to all of this.

KSLB said:

110 defender have never had a problem getting a good SWR on a fender.
Wilson beehive mount Try a PSM-1 Mount
Orbitor HD Antenna Same as me 3ft or 6ft??

Unit is wired direct to battery. Good no interference form wipers etc.

The lead seems ok, no continuity between the pin and the outer sheath. Good

Mounted on top of front wing 2' in front of windscreen.

Click to expand...

The location could well be your problem. Get the PSM-1 Mount as it fits to the rear of the landy above the gutter line.

KSLB said:

I will lose the extra cable tomorrow and see if that helps. Richard at Thunderpole said I would need the extra earth as it was a defender. New to all of this.

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He should be fooking ashamed of himself.

Tell him, "If Ally is a such a poor conducter", he should take two ally welding rods and stick 1 of each of em on the live and neutral terminals of a 240v Wall socket and take 1 rod in each hand. As the ally is such a **** conductor. He'll have nothing to be worried about.

How can it change the length of the antenna if there is no continuity between the antenna and the earth lead? Just curious not disagreeing, as I have said already new to this.

redhand said:

The location could well be your problem. Get the PSM-1 Mount as it fits to the rear of the landy above the gutter line.

Click to expand...

+1, conducting materials, esp close to the spring can give a high swr. Another possibility is where are you trying it? Close to buildings can effect readings.

Try in a fairly open space, remove aerial and get a mate to hold it as you test it. It's possible moving it a few inches forwards will make all the difference.

Thanks for the info, I did wonder why it needed an extra earth as some of the mirror mounts are aluminium anyway.

The Orbitor HD is 1.55m

I was in the middle of a field well away from buildings, trees etc.

If possible I would like to keep it on the wing as it has a hole through it now. I will get a pic tomorrow but thought it was far enough forward to be ok.

KSLB said:

I was in the middle of a field well away from buildings, trees etc.

If possible I would like to keep it on the wing as it has a hole through it now. I will get a pic tomorrow but thought it was far enough forward to be ok.

Click to expand...

Mines mounted on the back....couldn't get a decent reading for love nor money.....until I moved it up about 1 1/2''

Check the continuity between the wing and the chassis/body/engine earths. You are looking at a total electrical resistance of less than two ohms between all of them.

With radio transmissions, the 'ground plane' is an integral part of the setup, and acts as a kind of 'signal reflector'.

As you have mounted onto a wing, you will probably experience spurious reflections back to your antenna from the main body of your Landy, which is possibly why your SWR readings are high, and why it is recommended to mount the antenna as high as possible and away from other sources of reflected radiation, such as bodywork, buildings, etc.

An example of the importance of the ground plane is that a low powered rig can often out-perform a high powered one if it has a larger area of 'ground'.

In the days of home CB use, I made up the antenna from a length of ordinary single core electrical cable, with the ground plane (made from the same stuff) extending in three equal lengths and laid out at 120 deg between them. At 5W mine was out-performing most of the locals who were running 100W, and I was able to contact other users on the other side of the world, and they couldn't!

I use a "modulator" cb aerial on my 90 and its located in the aerial hole on the drivers side wing - so its quite close to the windscreen and i get a swr of just over 1:2

1 the patch lead between the CB and Vswr meter might be faulty
2 the Vswr meter might be faulty
3 the antenna might be faulty .I have had this in the past
4 on the antenna make sure the little grub screws are contacting metal and not the paint other wise the ant is not seeing the full length

DEFENDER90-DAZ said:

I use a "modulator" cb aerial on my 90 and its located in the aerial hole on the drivers side wing - so its quite close to the windscreen and i get a swr of just over 1:2

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Do you have an earth lead as well?

I am going to try mounting it on the roof rack and see if that helps but I may buy another lead another antenna and another SWR metre and see if I can find a faulty component.

Is there someone close with an SWR meter, so that you can compare the readings?

You should find that your levels come down with a roof mount.

KSLB said:

Do you have an earth lead as well?.

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Nope just normal wing skin with a chequerplate wing top

I don't know about your aerial but most standard ones are 'base loaded' so need to be mounted as high as poss so that all/most of the aerial clears the roof line and roof racks to reduce the reflected signal. If you can't or don't want to mount it high you need a 'top loaded' aerial.

That's what I thought... but I could just be talking sh*t.