Electrical UHF Wiring

Dec 2, 2019
5
1
3
Perth
#2
Hi Jaybird,
Something up my ally.
Regulated standard UHF CB Radio's put out 5 watts on transmit. Ohms law says it will use about 1/2 an amp @ 12 volts.
Tapping into existing bus bars on the vehicle is fine, but just make sure the fuse system supplying that bus will not be overloaded with the new load addition.
Even though its only 1/2 an amp, it still increases the load on the existing cables/fuse/terminations that were not designed for the extra load.
The safest way is direct to the battery via its own rated fuses ( both legs ) and rated cable. I use 2mm (or 14AWG in funny talk) double insulated figure 8 cable for the entire run up to 3 metres.. Guarantees next to no voltage drop over the run. For extra protection, I run all cable through corrugated conduit. Also something that a lot of people overlook or were not informed about. When running the coax to the antenna, especially if its out the front, don't run the coax passed the vehicle computer. Todays computers are fairly sensitive and a bit of RF running past when you transmit may cause the computer to do weird things. Mine disconnected cruise control for me.

I know it doesn't answer you original question but hope it helps a bit.

Torque
 

Boots in Action

Well-Known Member
Mar 13, 2017
919
822
93
Ferny Grove, Queensland
#3
Hi Jaybird,
Something up my ally.
Regulated standard UHF CB Radio's put out 5 watts on transmit. Ohms law says it will use about 1/2 an amp @ 12 volts.
Tapping into existing bus bars on the vehicle is fine, but just make sure the fuse system supplying that bus will not be overloaded with the new load addition.
Even though its only 1/2 an amp, it still increases the load on the existing cables/fuse/terminations that were not designed for the extra load.
The safest way is direct to the battery via its own rated fuses ( both legs ) and rated cable. I use 2mm (or 14AWG in funny talk) double insulated figure 8 cable for the entire run up to 3 metres.. Guarantees next to no voltage drop over the run. For extra protection, I run all cable through corrugated conduit. Also something that a lot of people overlook or were not informed about. When running the coax to the antenna, especially if its out the front, don't run the coax passed the vehicle computer. Todays computers are fairly sensitive and a bit of RF running past when you transmit may cause the computer to do weird things. Mine disconnected cruise control for me.

I know it doesn't answer you original question but hope it helps a bit.

Torque
Hi Jaybird,
Something up my ally.
Regulated standard UHF CB Radio's put out 5 watts on transmit. Ohms law says it will use about 1/2 an amp @ 12 volts.
Tapping into existing bus bars on the vehicle is fine, but just make sure the fuse system supplying that bus will not be overloaded with the new load addition.
Even though its only 1/2 an amp, it still increases the load on the existing cables/fuse/terminations that were not designed for the extra load.
The safest way is direct to the battery via its own rated fuses ( both legs ) and rated cable. I use 2mm (or 14AWG in funny talk) double insulated figure 8 cable for the entire run up to 3 metres.. Guarantees next to no voltage drop over the run. For extra protection, I run all cable through corrugated conduit. Also something that a lot of people overlook or were not informed about. When running the coax to the antenna, especially if its out the front, don't run the coax passed the vehicle computer. Todays computers are fairly sensitive and a bit of RF running past when you transmit may cause the computer to do weird things. Mine disconnected cruise control for me.

I know it doesn't answer you original question but hope it helps a bit.

Torque
Hello @Torquelimited, noted on your post that you believe it could have been stray RF energy too close to vehicle computer that caused disconnection of cruise control on your tug. Generally speaking, it is unlikely that RF energy would cause that problem as all good co-ax wiring to antennae is fully shielded to prevent interference from OUTSIDE sources and therefore should prevent any RF energy escaping outside until un-shielded at the antenna itself. Provided it is earthed at both ends of coax and at receiver/transmitter .Also the vehicle ECU is fully shielded in metal for weather proofing and electrical safety. However, if not connected to the chassis and instead to the NEG battery terminal, any change in voltage will be not be sensed by ECU as per the Red ARC sheet below.
"Current sensing in the vehicle's electrical system means that all additional electrical accessories must be grounded to the vehicle chassis or body , not to the main battery negative terminal in order to be taken into account by the ECU". This for your info @Jaybird too. There have been members on this forum who have, (or who have had friends) had serious issues with the electrical systems of modern tugs when neg lines from accessories have been connected to the neg battery terminal and not to the body or chassis.
 

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Boots in Action

Well-Known Member
Mar 13, 2017
919
822
93
Ferny Grove, Queensland
#5
Hello Boots.
Not believe it was stray RF. Proven
Relocate the coax away from the computer only and problem solved. Not other changes made.
Thanks for the response @Torquelimited . It goes to show that with all the technical and theory points indicating a potential problem, sometimes just the physical movement of simply moving a coax cable can be successful . However, the directions from Red Arc regarding negative connections to vehicle chassis should always be considered in this world of increasing technology and change as these too have been proven to be correct..
 
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