CB aerial Q's

[Sweety]

How you manage that, you got a burner? I have had CB from the 70's AM/FM with/without burners, and mobile never got more than a couple of miles, after all that is what the frequency is designed for, if we could all transmit 30 miles then every channel would be awash with interference from afar, cell phone are the same, if they had a greater range then the whole country would be awash with interference, hence the cell idea a small range around a local mast, granted there are those that transmit vast miles on 27 but they have very specialised antenna that are highly directional on great big masts, Rick

The rig was a Harvard 400m pushing 4w with a power mic the aerial was 6.5ft long on top of my old mk4 escort the guy I was chatting to said my signal wasn't strong on his gauge but was clear enough weather prob had a lot to do with it but that was the best I ever got from that set up but normally could transmit 10 miles easily

 

[Sweety]

Ahhh SWR is through the roof at 8-10 & can't get it down:doh:doh:doh not sure if it's my meter that is playing up so going to see if I can borrow one after that i'm pretty well stumped as it's the same set up I had in my old T2 & it was perfect:nenau

 

[jims-terrano]

Get a multimeter and test across aerial plug to see if there is a dead short. Also check outer of coax against outer metal of aerial mounting such as the metal case of mag mount. Centre pin of plug against the aerial too. Also test the patch lead in a similar manner.

 

[Sweety]

Get a multimeter and test across aerial plug to see if there is a dead short. Also check outer of coax against outer metal of aerial mounting such as the metal case of mag mount. Centre pin of plug against the aerial too. Also test the patch lead in a similar manner.

Thanks Jim:thumb2 tried all that & all tested ok but stripped down the mag mount & I think the outer braiding was just touching the bolt & also not getting a good earth so cleaned the base of the mag mount back to shiny metal & re-did the connections. To late to re-fit & test in the motor so stuck the mag mount on the dinning room rad & got the following ch1 1:1.8 ch20 1:1.7 & ch40 1:1.7 couldn't get it any lower as ran out of adjustment on the aerial:augie not sure what readings i'll get once fitted in the motor as there will be an extra meter of coax:nenau

 

[Sweety]

Fitted the CB into the truck today & the SWR was through the roof checked the coax & plugs with a multi meter all showing ok but I cut off the 90' PL plug I had got off evil bay & slightly cut down a normal PL plug for the back of the set as clearance is very tight & got a 1:1.7 SWR reading across all channels not great but it's as low as I can get it:augie
Anyway here's a pic for you's made up a little fascia to hold the CB in place & to mount the USB socket for my stereo & the switch for the footwell lights

 

[Paff]

I wanted to fit a CB antenna on the front on my NS roof rail, I already have an Amateur 2m/70cm antenna on the OSF roof rail, the SWR was good. I used the same mount and earthed the mount to the rail mounting bolt. The SWR for the CB antenna was way off the scale. I tried a different antenna and coax with the same result. I tried earthing the antenna mount to the door bolts and even direct to the chassis via a man step bolt, but still way too high SWR :doh

Ended up using a mag mount on the roof, then got good SWR.

Why?

 

[solarman216]

I wanted to fit a CB antenna on the front on my NS roof rail, I already have an Amateur 2m/70cm antenna on the OSF roof rail, the SWR was good. I used the same mount and earthed the mount to the rail mounting bolt. The SWR for the CB antenna was way off the scale. I tried a different antenna and coax with the same result. I tried earthing the antenna mount to the door bolts and even direct to the chassis via a man step bolt, but still way too high SWR :doh

Ended up using a mag mount on the roof, then got good SWR.

Why?

In my experience lack of ground plane on that kind of set is the reason, you need at least 600mm ground plane area, Rick

 

[Paff]

In my experience lack of ground plane on that kind of set is the reason, you need at least 600mm ground plane area, Rick

The Amateur radio antenna works OK, must be better or more tolerant kit.

 

[jims-terrano]

Very strange results especially with the mounting earthed direct to body. Sometimes RF energy will do as it please inspite of the laws of physics and our C&G quals Paff.
To get my Atas to work correctly I had to run an earth wire as you have done which did the trick. Before the solenoid in the atas was hunting all over before the 857 gave up and said high vswr. Now its straight to it in seconds.

Sweety 1:1.7 is acceptable really, if you were transmitting 100 watts I might be a little worried but 4 or 5 watts it is fine.

 

[briggie]

the mag mount provides a capactive effect for ground

 

[jims-terrano]

the mag mount provides a capactive effect for ground

They don't include that in Foundation Now do they :thumbs

Trust Briggies advice, he's got a lot of valuable experience with CB and also ham stuff too. If I had a CB question I'd be straight on the phone to Pete:thumbs

 

[The Patrolman]

mounted my aerial today and ran the cable through the trim to the dash.
only need the power doing now:thumb2

 

[The Patrolman]

easily unscrews too

 

[solarman216]

your roof tray will make a good ground plane, but will be weak on the off side, Rick

 

[Sweety]

On my old SWB had the aerial at the front of the roof rack & the SWR was great better than i'm getting with the mag mount

 

[SNH]

I'll be mounting mine on the roof rack once I get round to it

 

[The Patrolman]

easily unscrews too

Just had thought, what if I got a 17" stainless steel disk as a cover for my roofrack mounted spare wheel and used that as a ground plate for the aerial. High up and central.
Granted it would be a bit of a pain through the trees n bushes but it might just work????:nenau

 

[walshie]

Just had thought, what if I got a 17" stainless steel disk as a cover for my roofrack mounted spare wheel and used that as a ground plate for the aerial. High up and central.
Granted it would be a bit of a pain through the trees n bushes but it might just work????:nenau

Yes it would probably work well provided it is grounded to the roof rack, I.e. Not held down by a strap and insulated from the roof rack by the rubber tyre.
What frequencies are these systems typically using?
Assuming it's below 30mhz the whole vehicle will be acting as a ground plane, but having it central and high will give a good uniform radiation pattern :thumb2

 

[Paff]

Depending on the CB it 26 to 27Mhz