earthing a CB?

[(RIP) PLANK]

If you are making a temporary installation for a CB, so that it can easily be removed it seem fairly obvious that the case of the radio will need to be earthed or the coax screening will not be. I assume in a permanent installation this is done through the screw that fix it to the body? Would this temporary earth be best done to a remote fixed point? which is of course complex for a removable set up, or can it be done via the electricals? I.e. taking a wire from the cb body to the neutral of the power leads?

All ideas welcome, I understand good earthing of the coax screening / cb body is essential for a good SWR?

 

[762buzz]

fit one of these artifical earth thinges and dont worry about the earth plank is my best advise
want matter which motor its on

http://www.4x4cb.com/public/menu.cfm?Browse=Photos&Category=516

 

[Fez_uk]

those artificial antenna earth's are not that good, do it properly if you can to metal.

As for the radio, Don't think it's needed. alot of ham radios have a earth screw on there, But not really needed for the cb radio.

 

[762buzz]

Well got one fitted on mine with inline swr meter and not had any probs

Just thought save hassle if swapping kit about

Plus mine is on plastic roof bars

 

[(RIP) PLANK]

the issue is with a temporary instalation and a mag mount, slapped in the middle of the roof, so theres is nothing earthing the screening on the coax, so efectively it's not coax anymore :nenau

if you can picutre it, the plug that screws onto the back of the cb earths it to the cb's body/chasis and so it gets earthed that way - if the cb is screwed down to the car!

I have been experimenting with this today and by attatching a tmporay earth lead to the plug on the coax and to the car body the SWR reading drop drammaticaly :thumb2

 

[briggie]

not really needed as fez says for a cb , but if you really want to do it ,ensure the mounting bracket is mounted onto a metal surface with bolts etc, then the metal screws holding the radio to the bracket would normally suffice,also a good idea to run a little wire from your antenna mount to a good grounding point on your car body .

 

[(RIP) PLANK]

Thanks, but :nenau is it the way i typed it? :augie

 

[briggie]

just noticed you using a mag mount :doh , try running a little wire from the antenna socket at the back of the radio to the mounting bracket , im also assuming you are using a pre tuned antenna ?

 

[(RIP) PLANK]

just noticed you using a mag mount :doh , try running a little wire from the antenna socket at the back of the radio to the mounting bracket , im also assuming you are using a pre tuned antenna ?

to the mount itself? where exactly? :nenau

allegedly pre-tuned, but I don't think there can be such a thing in real life, can there? (unless of course you don't intend to transmit) As where you stick it counts for a lot. I have had a fiddle with it (the antenna :augie) parked in the middle of an open field and found that earthing the plug (therefore the coax screening) on the back of the CB had a dramatic effect on reducing the SWR reading.

pre-earthing the coax, had a few local chats and stuff, after earthing this afternoon, I spoke to a man in West Germany (though he could have been pulling my leg) Parked at the top of a very big hill obviously :thumb2

 

[briggie]

from the antenna socket to one or both of the screws holding the radio to the mounting bracket , crimp terminals or similar ,the mounting bracket will need to be fixed to the car body obviously , but the radio itself can be removed quite easily leaving the mounting bracket in place :thumb2

 

[(RIP) PLANK]

from the antenna socket to one or both of the screws holding the radio to the mounting bracket , crimp terminals or similar ,the mounting bracket will need to be fixed to the car body obviously , but the radio itself can be removed quite easily leaving the mounting bracket in place :thumb2

gotcha! that's what I have done, I tried both earthing it to the body and looping it back to the negative lead on the power supply, both seemed to have about the same effect, if anything linking it back to the neutral seems a little better :nenau

 

[Thomas-the-Terrano2]

surely the rig has a red and black lead, either within ciggy plug or
as i did in troll in its dash piggy backed them in to the radio power,

i used the permanent live feed so that it engine stalled then
wouldnt lose the channel memory or even use cb with ignition
off.

within in the radio the case is 'earthed' into the outer sleeve
of pl259 etc.

 

[(RIP) PLANK]

surely the rig has a red and black lead, either within ciggy plug or
as i did in troll in its dash piggy backed them in to the radio power,

i used the permanent live feed so that it engine stalled then
wouldnt lose the channel memory or even use cb with ignition
off.

within in the radio the case is 'earthed' into the outer sleeve
of pl259 etc.

The point here is this: imagine your CB just loose on the floor in the car, the power is connected yes, and yes the coax screening is "earthed" to the case of the CB. but if the CB body is not earthed to anything else - as it's sitting on a rubber mat' then (possibly depending on the make and model and internal configuration) neither is the Coax. you could check this by continuity testing between the negative and the case. This 'grounding' is usually achieved by fixing the CB to the vehicle body.

I achieved this 'grounding by looping a wire around the plug and piggy-backing it to the neutral lead.

This debate is only for 'temporary' CB connections, but may also be the case for some fixed cb's that are mounted to a plastic surface :thumb2

 

[Thomas-the-Terrano2]

but isnt its case earthed to its black 'return' power lead.

in troll the cb was sat in a plastic cubby hole, in the t2
it sits loose in the cubby behind gearstick on one of those
rubber? mats that prevent items slipping around and it works
perfectly. its red and black leads into a ciggy plug.

i do not follow how the rig works with out the black earth.

my earliest cb experience was a car unit, run by a mains
power supply , 2 wires between, the aeriel on a ground
plane on my bedroom carpet, not a good earth...

 

[(RIP) PLANK]

but isnt its case earthed to its black 'return' power lead.
in troll the cb was sat in a plastic cubby hole, in the t2
it sits loose in the cubby behind gearstick on one of those
rubber? mats that prevent items slipping around and it works
perfectly. its red and black leads into a ciggy plug.

i do not follow how the rig works with out the black earth.

my earliest cb experience was a car unit, run by a mains
power supply , 2 wires between, the aeriel on a ground
plane on my bedroom carpet, not a good earth...

red - some (maybe most) CB's do have a connection between the case and the black earth (negative) lead yes - but some don't and this is for a 'temporary' installation of one of the ones that doesn't!

blue - you are spot on it couldn't run without its "black earth" but this (if it isn't grounded to the CB case) will not earth the coax an therefore produce a high SWR reading.

the 'early CB you speak of probably had a metal case and therefor was most probably earthed to the negative and therefore bypassed all this!

Have you SWR tested yours or used a pre-tuned antenna and assumed? If so get a meter and check it :thumb2 I have found achieving a good SWR reading is so much easier if your coax and CB body are correctly grounded :thumb2

 

[Thomas-the-Terrano2]

pre tuned stinger, yes should check, though reception fine for convoy work.

all my rigs were metal cased, would expect even a plastic rig to earth
the aerial on its chassis.

fair point mag mounts thats al ive used , well since gutter mounts
disappeared.

cant beat a good earth, no harm in having more, were needed just not
felt the need on the six rigs used over last 30 years, unless rig was
labelled as needing additional earth.

 

[briggie]

without getting too technical , let us not confuse a rf earth with a safety ( ground ) earth

most vehicles these days are negative earth , which is normally sufficient for most installations , as the negative within the radio itself is connected to the vehicles earth , rf earth however is another matter

 

[(RIP) PLANK]

Briggie, i think that is what is getting confusing here, people mixing up the need for an effective ground plane from the need to earth the coax.

This wasn't intended to be a huge debate just food for thought, but I recommend getting an SWR meter and trying it. I was using a pre-tuned antenna and everything seemed fine, a simple earth wire and a bit of antenna 'tweaking' and the performance difference is amazing, might make no difference to your set up but it's free and it can't hurt anything :thumb2

 

[Fez_uk]

Magmount earth work on capacitance between the body and the mount. Idealy the mount should be bigger area but it's ok for 27mhz +

 

[(RIP) PLANK]

Magmount earth work on capacitance between the body and the mount. Idealy the mount should be bigger area but it's ok for 27mhz +

yep, but that is RF (ground plane) earth isn't it? and that's not the point I was making. :thumb2