Re: CB power
 

> If the coax is not properly grounded at both ends (again, I am talking
> about the SHIELDING part of the coax, not the CENTER part -- a coax has
> *TWO* things in it that carry electricity, doh!), your likely result is to
> be high SWR's. And the ground on both ends has to be to a ground that's at
> the exact same potential on both ends and said ground has to be the same
> ground as the transmitter because the transmitter is bouncing its waves
> courtesy of said ground.

The coax cable, has a 50ohms impedance, IF the RF circuit closes within the
coax.
That is the RF must travel through the center electrode, through the antenna
and then return through the shield of the cable.
In this case the RF currents in the core of the coax cable and in the shield
have opposite directions, and they cancel each other's electromagnetic
field, so that the cable doesn't radiate. That's why a coaxial cable is
used, so that the electromagnetic field is contained within the shield of
the cable (between the core and the shield).

If you create an alternative ground path, by hard grounding both ends of the
coax on the chassis, part of the RF will leak and will not return through
the coax shield, but through the car's body shell. This WILL change the
coax cable's impedance increasing the SWR, and WILL make it radiate part of
the signal causing interference to other cables parallel to it's route. You
could tune your RF amplifier output or your cable length to match the
impedances to reduce SWR, but you won't be able to reduce interference to
the car's circuits.

For a proper installation, you have to ensure that the RF circuit ground
path closes through the coax cable shield only.

A good way to achieve this, is by not grounding the CB end of the coax
cable, i.e. don't ground the chassis of the transmitter unit directly on the
car body.
The GND power supply wire of the CB must be used, which might have an RF
choke inline (otherwise one must be added) that prevents the RF circuit to
close through it.
And a relatively low frequency 27MHz RF is much more difficult to choke than
a higher 100MHz or 1 GHz RF signal. A choke must be added inline to the
positive power supply wire too, the RF can travel from the car's chassis
through the battery to the positive terminal easily.

If the antenna end of the coax needs to be grounded on the car's body
depends on the antenna used.
But if you have grounded the CB unit properly ONLY from it's GND power
supply wire, and have installed RF Chokes in both +12v and GND wires, then
you will not have problems for either case.

Regards,

Bill Spiliotopoulos.
'96 XJ,
'06 TJ.

Re: CB power
 

> If the coax is not properly grounded at both ends (again, I am talking
> about the SHIELDING part of the coax, not the CENTER part -- a coax has
> *TWO* things in it that carry electricity, doh!), your likely result is to
> be high SWR's. And the ground on both ends has to be to a ground that's at
> the exact same potential on both ends and said ground has to be the same
> ground as the transmitter because the transmitter is bouncing its waves
> courtesy of said ground.

The coax cable, has a 50ohms impedance, IF the RF circuit closes within the
coax.
That is the RF must travel through the center electrode, through the antenna
and then return through the shield of the cable.
In this case the RF currents in the core of the coax cable and in the shield
have opposite directions, and they cancel each other's electromagnetic
field, so that the cable doesn't radiate. That's why a coaxial cable is
used, so that the electromagnetic field is contained within the shield of
the cable (between the core and the shield).

If you create an alternative ground path, by hard grounding both ends of the
coax on the chassis, part of the RF will leak and will not return through
the coax shield, but through the car's body shell. This WILL change the
coax cable's impedance increasing the SWR, and WILL make it radiate part of
the signal causing interference to other cables parallel to it's route. You
could tune your RF amplifier output or your cable length to match the
impedances to reduce SWR, but you won't be able to reduce interference to
the car's circuits.

For a proper installation, you have to ensure that the RF circuit ground
path closes through the coax cable shield only.

A good way to achieve this, is by not grounding the CB end of the coax
cable, i.e. don't ground the chassis of the transmitter unit directly on the
car body.
The GND power supply wire of the CB must be used, which might have an RF
choke inline (otherwise one must be added) that prevents the RF circuit to
close through it.
And a relatively low frequency 27MHz RF is much more difficult to choke than
a higher 100MHz or 1 GHz RF signal. A choke must be added inline to the
positive power supply wire too, the RF can travel from the car's chassis
through the battery to the positive terminal easily.

If the antenna end of the coax needs to be grounded on the car's body
depends on the antenna used.
But if you have grounded the CB unit properly ONLY from it's GND power
supply wire, and have installed RF Chokes in both +12v and GND wires, then
you will not have problems for either case.

Regards,

Bill Spiliotopoulos.
'96 XJ,
'06 TJ.

Re: CB power
 

> If the coax is not properly grounded at both ends (again, I am talking
> about the SHIELDING part of the coax, not the CENTER part -- a coax has
> *TWO* things in it that carry electricity, doh!), your likely result is to
> be high SWR's. And the ground on both ends has to be to a ground that's at
> the exact same potential on both ends and said ground has to be the same
> ground as the transmitter because the transmitter is bouncing its waves
> courtesy of said ground.

The coax cable, has a 50ohms impedance, IF the RF circuit closes within the
coax.
That is the RF must travel through the center electrode, through the antenna
and then return through the shield of the cable.
In this case the RF currents in the core of the coax cable and in the shield
have opposite directions, and they cancel each other's electromagnetic
field, so that the cable doesn't radiate. That's why a coaxial cable is
used, so that the electromagnetic field is contained within the shield of
the cable (between the core and the shield).

If you create an alternative ground path, by hard grounding both ends of the
coax on the chassis, part of the RF will leak and will not return through
the coax shield, but through the car's body shell. This WILL change the
coax cable's impedance increasing the SWR, and WILL make it radiate part of
the signal causing interference to other cables parallel to it's route. You
could tune your RF amplifier output or your cable length to match the
impedances to reduce SWR, but you won't be able to reduce interference to
the car's circuits.

For a proper installation, you have to ensure that the RF circuit ground
path closes through the coax cable shield only.

A good way to achieve this, is by not grounding the CB end of the coax
cable, i.e. don't ground the chassis of the transmitter unit directly on the
car body.
The GND power supply wire of the CB must be used, which might have an RF
choke inline (otherwise one must be added) that prevents the RF circuit to
close through it.
And a relatively low frequency 27MHz RF is much more difficult to choke than
a higher 100MHz or 1 GHz RF signal. A choke must be added inline to the
positive power supply wire too, the RF can travel from the car's chassis
through the battery to the positive terminal easily.

If the antenna end of the coax needs to be grounded on the car's body
depends on the antenna used.
But if you have grounded the CB unit properly ONLY from it's GND power
supply wire, and have installed RF Chokes in both +12v and GND wires, then
you will not have problems for either case.

Regards,

Bill Spiliotopoulos.
'96 XJ,
'06 TJ.

Re: CB power
 

Mike Romain wrote:
> Fusing the negative line is very important because if the vehicle loses
> a ground for whatever reason. it can/will pull one through the
> transmitter and let the magic smoke out of the transmitter big time.

I would NEVER fuse the electrical ground line because if that fuse
happens to go...and fuses do go...your radio circuit WILL find an
alternate ground path and you will not likely appreciate it's choice.
The likelihood of a body ground strap going bad is far less likely than
a simple inline fuse. If you're paranoid about body straps going bad,
replace it during your radio installation.

tw

Re: CB power
 

Mike Romain wrote:
> Fusing the negative line is very important because if the vehicle loses
> a ground for whatever reason. it can/will pull one through the
> transmitter and let the magic smoke out of the transmitter big time.

I would NEVER fuse the electrical ground line because if that fuse
happens to go...and fuses do go...your radio circuit WILL find an
alternate ground path and you will not likely appreciate it's choice.
The likelihood of a body ground strap going bad is far less likely than
a simple inline fuse. If you're paranoid about body straps going bad,
replace it during your radio installation.

tw

Re: CB power
 

Mike Romain wrote:
> Fusing the negative line is very important because if the vehicle loses
> a ground for whatever reason. it can/will pull one through the
> transmitter and let the magic smoke out of the transmitter big time.

I would NEVER fuse the electrical ground line because if that fuse
happens to go...and fuses do go...your radio circuit WILL find an
alternate ground path and you will not likely appreciate it's choice.
The likelihood of a body ground strap going bad is far less likely than
a simple inline fuse. If you're paranoid about body straps going bad,
replace it during your radio installation.

tw

Re: CB power
 

Mike Romain wrote:
> Fusing the negative line is very important because if the vehicle loses
> a ground for whatever reason. it can/will pull one through the
> transmitter and let the magic smoke out of the transmitter big time.

I would NEVER fuse the electrical ground line because if that fuse
happens to go...and fuses do go...your radio circuit WILL find an
alternate ground path and you will not likely appreciate it's choice.
The likelihood of a body ground strap going bad is far less likely than
a simple inline fuse. If you're paranoid about body straps going bad,
replace it during your radio installation.

tw

Re: CB power
 

L. Ron Waddle wrote:

>
> It's not mylar. it is a conductive plastic.

--------!

I have tested 'many' mag mount antennas and have had to reposition
dozens that allowed the metal cup's side to touch the van body creating
an electrical ground path shorting out the coax causing massive
transmitter packet loss.

I actually read the Friestick site and from there and I Quote:

Magnet mounts rely on high resistance, capacitance grounding

End Quote.

I do see lots than need a grounded mount implying the coax shield might
be grounded at the outer end though, so I figure I must have seen NGP
mounts with isolated COAX mostly for some strange reason.

That is still a good reason for the Automotive makers wanting 'both' the
power and ground fused so no matter which way a short starts or a
vehicle ground gets lost, the power surge will hit a fuse before letting
the magic smoke out of the transmitter.

Oh, the booklets also do 'just' say 'transmitter', they do not care what
'type' of transmitter is being installed.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Re: CB power
 

L. Ron Waddle wrote:

>
> It's not mylar. it is a conductive plastic.

--------!

I have tested 'many' mag mount antennas and have had to reposition
dozens that allowed the metal cup's side to touch the van body creating
an electrical ground path shorting out the coax causing massive
transmitter packet loss.

I actually read the Friestick site and from there and I Quote:

Magnet mounts rely on high resistance, capacitance grounding

End Quote.

I do see lots than need a grounded mount implying the coax shield might
be grounded at the outer end though, so I figure I must have seen NGP
mounts with isolated COAX mostly for some strange reason.

That is still a good reason for the Automotive makers wanting 'both' the
power and ground fused so no matter which way a short starts or a
vehicle ground gets lost, the power surge will hit a fuse before letting
the magic smoke out of the transmitter.

Oh, the booklets also do 'just' say 'transmitter', they do not care what
'type' of transmitter is being installed.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Re: CB power
 

L. Ron Waddle wrote:

>
> It's not mylar. it is a conductive plastic.

--------!

I have tested 'many' mag mount antennas and have had to reposition
dozens that allowed the metal cup's side to touch the van body creating
an electrical ground path shorting out the coax causing massive
transmitter packet loss.

I actually read the Friestick site and from there and I Quote:

Magnet mounts rely on high resistance, capacitance grounding

End Quote.

I do see lots than need a grounded mount implying the coax shield might
be grounded at the outer end though, so I figure I must have seen NGP
mounts with isolated COAX mostly for some strange reason.

That is still a good reason for the Automotive makers wanting 'both' the
power and ground fused so no matter which way a short starts or a
vehicle ground gets lost, the power surge will hit a fuse before letting
the magic smoke out of the transmitter.

Oh, the booklets also do 'just' say 'transmitter', they do not care what
'type' of transmitter is being installed.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)