[V8-Ninety]

Sorry I know this has been done to death but none of the other posts have helped me...

Bought a kit with a gutter mount and a long aerial from thunderpole I mounted the aerial above my rear door. On channel 1 im getting a ref of around 2 channel 40 is slightly over 1.5. This seems to suggest my aerial is too short but the whip is at full height. I then tried too see if it was an earthing problem by removing the paint from the gutter and mount as well as running an earth cable 1st from mount to battery then from mount to rear crossmember when that failed... neither of these have made any difference. I want to get the best range possible. Any help is appreciated.

 

[Pikey]

Nowt wrong with what you've got, Moving the mount is probably the only thing likely to change it.

Or you could trim a Millimeter or so off the bottom of the aerial.

 

[V8-Ninety]

Wow I was expecting abuse haha where would you suggest moving it to? I thought it was too short though?

 

[brian47]

A "perfect" VSWR (Voltage Standing Wave Ratio) reading with a high frequency aerial mounted on a vehicle is almost un-achieveable, largely due to the practical length of what can be fitted to the vehicle.

The most effective aerial length for mobile work has been found to be a quarter wave length.

For vhf and uhf private mobile radio (PMR) installations the length is quite practical, uhf is around 6 inches, high band vhf (150 MHz) about 18 inches and low band vhf (70 MHz) about 1 metre but for CB on the 27 MHz band a quarter wave is something like a bit less than 3 metres.

For HF, aerial designers and manufacturers try to make a shorter practical length appear longer electrically by introducing some sort of loading device, usually a coil either at the bottom or some point along the length of the aerial. The main drawback of doing this that it often makes the job of mounting and fine tuning the aerial somewhat twitchy and more difficult.

Couple that with the need for a "counterpoise", or the ground which is required for the aerial to work against; on a vehicle this is usually the bodywork.
The size of the counterpoise is usually required to be about an eighth of a wave length, you can see that the lower the frequency band being used, the larger this also needs to be.

Given all the difficulties involved with getting a high frequency aerial to work on a vehicle all that can be said is that the SWR should be as low as possible remembering that the perfect figure of 1:1 is almost impossible; in fact if I ever see that figure I start suspecting an aerial cable fault.

In general, a figure of better than say 3:1 is acceptable.

I know this is somewhat long-winded, but I thought that a bit of explaination might be needed.

 

[V8-Ninety]

So what would you suggest I do to improve my swr readings?

 

[brian47]

So what would you suggest I do to improve my swr readings?

Accept it as it is.

 

[everlatesparky]

A 6ft firestick on a limpet base!!!

 

[V8-Ninety]

Is a limpet a mag mount? Dont fancy screwing it to the roof haha

 

[Spunka]

sorry another dumb question
No part of my arial mount is touching metal, after reading a lot of posts i fort the earth ran down the outer coax through the cb
do i need an earth from the bottom of the airal mounting to the body aswell

All im getting is noise, Ive got an SWR on order but can it be that far out that you cant pick any thing up

It all seemed alot easyer back in the 80s

 

[Bromsgrove Defender]

sorry another dumb question
No part of my arial mount is touching metal, after reading a lot of posts i fort the earth ran down the outer coax through the cb
do i need an earth from the bottom of the airal mounting to the body aswell

All im getting is noise, Ive got an SWR on order but can it be that far out that you cant pick any thing up

It all seemed alot easyer back in the 80s

FFs

Yup you need the aerial to be grounded

And good reception int where the problem is. The problem lies in damaging your output stages by transmitting with a mismatched aerial

Best find someone you can borrow an SWR meter from

 

[Paul D]

I now carry an swr meter .. if you can wait till Tong in November we'll have a crack at it then, or pop over sometime, but I'm away every weekend now till about the end of November!

 

[Spunka]

FFs

Yup you need the aerial to be grounded

And good reception int where the problem is. The problem lies in damaging your output stages by transmitting with a mismatched aerial

Best find someone you can borrow an SWR meter from

cheers, I did actually connect a temp clip on earth to it and will now make it permanent

 

[Spunka]

I now carry an swr meter .. if you can wait till Tong in November we'll have a crack at it then, or pop over sometime, but I'm away every weekend now till about the end of November!

Cheers , i have one on order , if I get more stucker i will give you a shout

 

[V8-Ninety]

Ill spend another day ####ing about with my aerial and if that fails maybe it would work better if I got someone that knows what they're doing to fix it

 

[Bromsgrove Defender]

Ill spend another day ####ing about with my aerial and if that fails maybe it would work better if I got someone that knows what they're doing to fix it

It's fairly easy really.


If you're struggling to get a decent swr have a look where others have mounted theirs.
Even better if you're in a carpark and the owner is there just ask em how they did theirs

Mines mounted on the A bar. Got the best swr I've ever had

 

[V8-Ninety]

Got one of those bayonet quick release mechanisms (its stiff as #### would be quicker unscrewing the aerial) but it lifted the aerial by miles and the swr is near perfect. 1.3 ish on ch 1 and channel 20 and 40 both read 1.5 well chuffed

 

[Spunka]

Just rehashing this old chestnut coz everyone loooves a CB thread


I have been arsing about with my newish SWR meter today,
With the hand of a multi meter (set on beep) I found the center pin on my aerial mount was not touching the dimple on end of the springer aerial its self,
So thats why my readings were all in the red,
The spunking nut wouldnt come of the mounting so I choped the lot off and now have another different type

mount on order



Im gunna mount one of these through the roof on a strengthening plate

 

[Spunka]

WooHoo Im all CBed up now
I got a base mounting from Maplins and a angle adapter
SWRed it up and bingo
Just need some one to talk to now


Here's a link ,may be of use to some one
SWR Troubleshooting Flowchart | Right Channel Radios