CB Radio advice.

soz kuunder, yeah i got it all sorted today. had some other points to put right before i fitted it. all seems fine tho. will advise that you also get the swr meter as its like £8 on that april offer and i found that it changed hugely depending on where i put it. i have done away with my old cd player ariel (mp3 went in today aswell) so i put the cb ariel there and works fine. meter reads about 2.5 with it full size

will simply cutting the ariel down in length do it?

If you do, a teeny bit at a time & of course it may be cos' it's too short!

its like 61" long, and its mounted on the wing not 2' from the radio unit so must be too long surely?????

It's all to do with the wavelength and multiples or fractions thereof. I can't be arsed to look up the science now as it's Bank hols & I've got beer, but cutting a fraction too much orf can send you SWR reading off the scale and bust your radio if you try to transmit.

i think ill leave it as is for now. book says anything under 3 on the swr thingy mabob is fine and safe for it so good enough.... maybe try a smaller ariel at a later date and see what that does.

This is the guide I usually point people to: What is SWR? | CB Radio Guide | THUNDERPOLE

If you want to know if your ariel ideally needs to be shorter or longer, as well as checking the SWR on ch20, check it on 1 & 40 too.

If it's lower on ch1 the ariel is too long.
If it's lower on ch40 the ariel is too short.

2.5 is ok for short range keeping in touch when laning, but you aren't going to get a huge range with it.

If you change to a shorter twig, even if you get a marginally better SWR reading you're going to get less range because of the less efficient ariel.

Big ariel, middle of the roof with a big **** off square steel plate bolted unnerneath it is THE best mounting, but ain't exactly practical or pretty. Like I said, if it's just for keeping in touch when laning then I wouldn't **** around with it too much & certainly wouldn't spend anymore money.

cheers grippa ill take a look and see what comes of it. like i said i got the 60 odd inch one mounted on the wing now and it looks like a big boys rc car! but i have some time untill she goes back out in public so ill have a play. having bit of a serious maintanance spree at the mo. oils, wiring, holes, u name it im on it!

no ground plate. thats the problem i bet. followed the instructions and it just says to connect the negative, nothing about grounding the ariel itself!

For the antenna to work correctly it needs a good earth known as a ground plane.

You can run a thick wire from the base of antenna off a plate etc to the body this will do and adjust antennna correctly swr wants to be lower than 1.5 to work at it's best, but 2-3 will work just not over a long distances.

We had a multiband rig known as a sidebander am/fm/ssb we used to chat all over the world when parked up after a good day out in the field but you need the antenna correct to do this.

Have fun what ever you do thats the game.

yeah im enjoying learning it all to be honest, as much as i enjoy driving it. ill give that a go and take the meter reading and see what it does.

ok i finally got round to earthing the cb ariel today and was looking forward to finally testing it out. problem is that now the swr reading came back at 10+!!! not good! going now to check if its too long or too short but if i do need to start cutting it down, how much should i cut off at a time??

This is a good guide

Advice Pages , How To Use An SWR Meter

thainy said:

ok i finally got round to earthing the cb ariel today and was looking forward to finally testing it out. problem is that now the swr reading came back at 10+!!! not good! going now to check if its too long or too short but if i do need to start cutting it down, how much should i cut off at a time??

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Have you got a good earth for this aerial were is it mounted what type of aerial is it?

The coax is it new is there a short have you checked with a multi meter?

Anything below 2 is fine 10+ sounds you may also have it on the wrong setting which meter are you using? is it a power/swr meter?

its mounted in place of the original ariel on the front wing. with no ground i got a reading of about 2.5. i thought the ground was good but i guess i was wrong. its all brand new kit, everything. its the midland 98, mentioned on this thread earlier. april package deal with the large springer. just a swr meter, not power, just has the fwd and ref settings.

just noticed i have been letting go of the transmit button between checking it on fwd and ref, would that matter?

i think i will try get a better ground and if that doesnt work i think i'll move it.

anyone with the same setup please let me know how u got on

A springer type aeriel mounted on the front wing will give you problems with SWR.
Due to amount of "load" (ie the amount of actual metal of the aeriel = the spring part) being sheilded with the bodywork. A better aeriel would be to have the "spring" ie the extra coils, near to the top.
I had one on the rear of a 90, and although near to the roofline, it barely managed to SWR reasonable. (see photo)
I changed it to a "top-load" aeriel, and now have perfect SWR. (I'll see if I can find a piccy of that)

For the disco they make a bracket that goes on the spare wheel carrier can't you make something similar or just fit a mag mount which is the easiest option.?

It's deffo a grounding problem once you sort this out you will be able to adjust the swr correctly and the cb will work as it should at full power.

Yes you must hold the ptt the button on the mike in when checking the swr it's the transmit side your doing not the receive.

It's nothing to do with grounding! do you scrape the paint off the roof when you put a mag mount on? no, course you don't!
So long as the outer part of the coax connects to the aeriel mount correctly, and to the CB correctly, it'll be grounded OK.
It's down to the propagation of the aeriel in relationship to the ground plane, ie your bodywork. If you're trying to put a short aeriel on the wing, or below roof line, you'll have real problems SWR'ing, you could put a short aeriel in the roof, roofrack etc. and have no problems. Below the roofline, the *radio waves* bounce back at the aeriel (easy way of explaining) so you need enough of the aeriel showing above the roofline to get a decent SWR reading.
A simple DV27 would work on the wing or on a bracket from the spare wheel, that's because the DV27 aeriel is top-loaded, ie there lots of wire wound up under the plastic near to the top, therefore making the propergation very much stronger at the top of the aeriel than near to the mounting point.
I use what is basically a DV27 but with a spring at the bottom, so that when hitting trees etc, it'll bend over out of the way, rather than breaking either the aeriel or the bracket.
First piccy is of the aeriel mounted on my Disco. you can see the length of it.
2nd piccy is of the base of the aeriel, the spring is purely so the thing will bend out of the way when a low tree comes along.
3rd piccy shows the top of the aeriel, under the grey is where the wire is wound, the little piece in the top is for adjusting for SWR.
I guarantee that with this type of aeriel you'll get a decent SWR reading, even on the wing or rear spare wheel carrier (providing you've soldered the coax ends on correctly!)

I've fitted these aeriels to a number of 4x4's and had excellent results with them.

Gafferjim said:

It's nothing to do with grounding! do you scrape the paint off the roof when you put a mag mount on? no, course you don't!

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With anything other than a mag mount you should cut throught the paint to get the best ground, this includes gutter mounts, where the screw should cut down to bare metal. I could well be wrong but with mag mounts I thought it was the magnetic field of the magnet that allowed the ground plane to propagate into the bodywork?