Pages: [1]   Go Down

Author Topic: Mobile Radio Best Installation Practices  (Read 456 times)

AI5BC

  • Posts: 456
    • HomeURL
Mobile Radio Best Installation Practices
« on: February 10, 2023, 09:43:42 PM »

I hope this helps clear up a few questions found here and on QRZ about mobile installs. I see conflicting advice, and a lot of it is dangerous and lacks fundamentals. The two most important aspects of the installation are Power termination points and Cable routing. Although well-intentioned, many hams and even radio manufacturers recommend outdated and hazardous installation practices concerning the radio's power wiring. Both fail to look at the circuit they create when they recommend connecting the radio's negative power wire directly to the vehicle's battery negative return post.

The first drawing clearly shows the circuit. You place your radio in a dangerous ground loop. Note the "Battery Negative Chassis Return Wire." Pop your hood, and you will see it. That wire carries all the vehicle current back to the battery negative terminal from the chassis. When you connect the radio's battery negative directly to the battery, your radio is in parallel. It is a piece of wire hopelessly lost in a ground loop. Your radio has a vehicle current flowing through it. It is undeniable.

What makes it dangerous is that if something happened to the vehicle's bonding jumper, you would not know it until you tried to start the vehicle. Place the key in the ignition, and all the bells and whistles work because your radio is now the bonding jumper. Turn the key, and the cab fills with smoke with engine cranking current flowing through your coax and radio negative wire.

It is dangerous and a root cause of many RFI issues. You are forcing vehicle current through your ground plane, aka Common-Mode noise. Popps and clicks, alternator whine, ignition noise. It is all flowing through your radio. Try an experiment if you have a clamp-on amp meter. Clamp the radio negative, turn the radio off, monitor the amp-meter, crank the engine, turn on accessories, and watch the current flow.



The solution is simple, terminate the negative radio wire to the chassis. The radio positive goes directly to the battery, not the negative. Where do you terminate the negative to the chassis? Due to the negative being both power and ground, you keep it short as possible, measured in inches. You do not want to drag it under the hood, and there is no reason to in modern vehicles. All new vehicles have electrical hard points under the seats and firewall. For example, all have high-power accessories under the seats, like sub-woofer amps, high-powered audio amps, electric seats, heated seats, and Inverters. Find one of the plugs and locate the ground wire; it will go to a hard point near a seat bolt for high-current connections. Find the green wires going to the vehicle chassis

For best Mobile Installation Practices, I recommend you use what the pros use. To do mobile electronic installation work for public safety, first responders, the military, any government agency, or utility, you must be certified and follow "Motorola R56 Appendix G Mobile Installation Standards and Techniques".
Standards and Guidelines for Communication Sites

https://www.sno911.org/images/Documents/WirelessTech/RRP/Policies/R56_Mobile_Installation_Standards_and_Techniques_2.pdf

G.10 Power Wiring warns the installer of the dangers of terminating anything directly to the battery negative term post and never using a fuse on a negative wire. It contains excellent information on anything you want about mobile radio installs, right down to tools and materials. It even tells you how to install radios on motorcycles and how to mount antennas on fiberglass.

So next time someone tells you to connect your negative radio wire directly to the battery, say no, thanks Sammy, not in my vehicle.
Logged

VK3KTO

  • Member
  • Posts: 18
Re: Mobile Radio Best Installation Practices
« Reply #1 on: February 10, 2023, 10:53:55 PM »

I once worked on BMC vehicles and have seen choke or accelerator cables melt when a fault developed with the battery earth strap, fortunately no radios fitted!   
Logged

KG2QM

  • Posts: 11
    • HomeURL
Re: Mobile Radio Best Installation Practices
« Reply #2 on: February 11, 2023, 02:34:03 AM »

A few years ago that happened to the 2010 Beetle my wife had. Bad connection from battery to chassis; she went to start it and it tried to find a ground through a different route. Melted some wiring, I can't remember which part of the wiring; had to be towed and repaired.
Mike - KG2QM
Logged

KC0W

  • Member
  • Posts: 1540
Re: Mobile Radio Best Installation Practices
« Reply #3 on: February 11, 2023, 03:32:35 AM »

 It's amazing how AI5BC will be a complete asshole in 99% of his posts and then suddenly post something actually informative...............Looks like we will have to wait another 99 posts now. 

                                                                       Tom KH0/KC0W   
Logged

AC7CW

  • Member
  • Posts: 1789
Re: Mobile Radio Best Installation Practices
« Reply #4 on: February 11, 2023, 09:47:18 AM »

 A mag-mount will remove the coax from the ground loop.

I like to use a mag-mount and a second battery to supply tx power. I charge the second battery from the cigar lighter using an isolating resistor to limit key-down current out of the cigar lighter. I've thrown that setup together in minutes using duct tape to mount the battery [lead-acid] to the radio, and used it for years with no problems... on a newer car I'd add a diode to the current limiting resistor in case the car battery was disconnected to avoid current from the added battery getting into the car's stuff...
Logged
Novice 1958, 20WPM Extra now... (and get off my lawn)

AI5BC

  • Posts: 456
    • HomeURL
Re: Mobile Radio Best Installation Practices
« Reply #5 on: February 11, 2023, 10:29:17 AM »

A mag-mount will remove the coax from the ground loop.
Not the radio.
Logged

AC7CW

  • Member
  • Posts: 1789
Re: Mobile Radio Best Installation Practices
« Reply #6 on: February 11, 2023, 12:00:19 PM »

Single point ground = No ground loop...

Not that single point grounds at frequencies above audio mean anything in more complicated situations like design of a printed circuit board but we're talking about DC here...
Logged
Novice 1958, 20WPM Extra now... (and get off my lawn)

K6CPO

  • Member
  • Posts: 838
Re: Mobile Radio Best Installation Practices
« Reply #7 on: February 11, 2023, 12:42:45 PM »

OK. I just went out and changed the grounding on the radio in my truck by the simple expedient of removing the negative lead from the battery and attaching it to an existing ground point on the firewall.

You guys happy now?
Logged

KF6QEX

  • Member
  • Posts: 788
Re: Mobile Radio Best Installation Practices
« Reply #8 on: February 11, 2023, 01:14:36 PM »

OK. I just went out and changed the grounding on the radio in my truck by the simple expedient of removing the negative lead from the battery and attaching it to an existing ground point on the firewall.

You guys happy now?

It depends ; how much did you tighten the nut and what is the most recent calibration date of your torque wrench ?
Logged
sdrawkcab daer tseb si txet sihT

K6CPO

  • Member
  • Posts: 838
Re: Mobile Radio Best Installation Practices
« Reply #9 on: February 12, 2023, 10:57:24 AM »

OK. I just went out and changed the grounding on the radio in my truck by the simple expedient of removing the negative lead from the battery and attaching it to an existing ground point on the firewall.

You guys happy now?

It depends ; how much did you tighten the nut and what is the most recent calibration date of your torque wrench ?

I spent 20 years in aviation manufacturing. I think I know how to tighten a net. You really need to stop assuming everyone else is an idiot.
Logged

AI5BC

  • Posts: 456
    • HomeURL
Re: Mobile Radio Best Installation Practices
« Reply #10 on: February 12, 2023, 11:42:17 AM »

I spent 20 years in aviation manufacturing. I think I know how to tighten a net. You really need to stop assuming everyone else is an idiot.
What does a net have to do with a radio in a vehicle?
Logged

KD6VXI

  • Member
  • Posts: 1021
Re: Mobile Radio Best Installation Practices
« Reply #11 on: February 18, 2023, 09:39:44 AM »

A few years ago that happened to the 2010 Beetle my wife had. Bad connection from battery to chassis; she went to start it and it tried to find a ground through a different route. Melted some wiring, I can't remember which part of the wiring; had to be towed and repaired.
Mike - KG2QM

This is exactly why factory power connector s come fused in the positive and negative side.

--Shane
WP2ASS / ex KD6VXI
Logged

KD6VXI

  • Member
  • Posts: 1021
Re: Mobile Radio Best Installation Practices
« Reply #12 on: February 18, 2023, 09:41:16 AM »

It's amazing how AI5BC will be a complete asshole in 99% of his posts and then suddenly post something actually informative...............Looks like we will have to wait another 99 posts now. 

                                                                       Tom KH0/KC0W

Well, there is the just glaring error he made in the beginning talking about carrying current back to return at the negative terminal.

Did physics change last night?  Negative IS the electron source.

--Shane
WP2ASS / ex KD6VXI
Logged

AC7CW

  • Member
  • Posts: 1789
Re: Mobile Radio Best Installation Practices
« Reply #13 on: February 18, 2023, 03:43:48 PM »

A mag-mount will remove the coax from the ground loop.
Not the radio.
Come to think of it I just put the radio on the passenger seat, never connected it to ground. If I had a passenger I put the radio on the floor and talked to the passenger rather than to hams... I think I'll always use this method actually, if I permanently mount the radio I'll insulate it... no ground loop, no holes in the firewall, if magmount coax is out the window then no holes anywere but that look is not what I'm after, instant swap of radio and antenna to any car with a cigar lighter... outside of that there must be a more elegant solution, I'll wait for it... I was getting the lead-acid battery from a surplusser for $7, not much reason to worry about care and feeding of same... I'm sure there are more "perfectionistic" or "professional" methods but that is not elegant, Einstein said to make things as simple as possible but not too simple, that is elegance...
Logged
Novice 1958, 20WPM Extra now... (and get off my lawn)
Pages: [1]   Go Up