Planning an install, help with finishing touches...

Discussion in 'Mobile Radio Systems' started by N8MLP, Sep 9, 2019.

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  1. W5GX

    W5GX Ham Member QRZ Page

    Well, there can be more than one correct way to do a thing, but some are just better.

    It wasn't a trap - just curious.
  2. KF5LJW

    KF5LJW Ham Member QRZ Page

    I should have been more clear but you kind of joined in after the start of the movie so to speak. My first replay was preferred practice by terminating the radio negative to the chassis as close to the radio as possible. I stand by that as first choice for a number of reasons, all performance and safety related.

    My later reply was knowing the OP already had his radio negative terminated to the Battery Term Post under the hood and offered him a second option that would at least make it safe, and break the Ground Loop preventing vehicle current to flow trough the radio negative, coax, and chassis. So I offered remove the radio negative from the Battery Term Post to the Chassis where the other end of the vehicle battery cable terminated. Pretty easy to see and trace down with no added length of wire.

    If given a choice terminate as close to the radio as possible. The reason is pretty, the chassis and frame if there is one forms a Equipotential Ground Plane, and the auto manufactures designed the chassis/frame to be used as a conductor for both load currents and signal reference. You want to keep your battery Negative as short as possible because not only is it your current carrying conductor, but also your ground or 0-Volt Reference Point. If you extend the length to run it under the hood only increases your chances of RFI interference in your RX like sensor and control wiring radiating noise into your ground circuit.

    So both methods I stated removed the Ground Loop by using the chassis. I gave the OP an easy lazy way out making it safe and getting vehicle current out of the radio.

    Hope that helps to clear it up.
    AI7PM and KX4O like this.
  3. KF5LJW

    KF5LJW Ham Member QRZ Page

    No Flip Flopping at all. Very consistent, use the chassis for negative, and battery for positive. Been doing this for 40 years professionally, not an amateur, and now mange a utility fleet radio with over 1200 mobiles and 2800 portable. We figured this out 40 years ago when radio coxes mysteriously burnt up. We figured out the problem real fast not to connect radio negative directly to the battery term post. you put the radio (Negative > Coax) in parallel with the battery negative chassis bonding jumper.

    If you advocate connecting to the battery negative term post, then you have no biz playing radio or anything electrical because you fail to understand extremely basic parallel circuit laws. I also understand electrical ground and ground extremely well. wrote a few books on the subject. In a car electrical system chassis and electrical ground are the exact same point, anywhere along the length of the Ground Plane. Pop your car hood and have a look. Wire from battery goes directly to chassis. Now in marine, aircraft, and building power and wiring everything is separated and isolated. No normal load current is allowed to use a ground circuit as a circuit conductor as that can be extremely dangerous and corrosive. But not in automotive, ground is both a normal load current conductor, ground, and signal reference. I is used just like a Ground Plane on a circuit board. The chassis is being used in place of ground and circuit conductor.
    KX4O likes this.
  4. KX4O

    KX4O Ham Member QRZ Page

    This has standing in some of the various specs for vehicle power systems. This from MIL-STD-1275D...

    4.4 Polarity. The negative of the vehicle power supply system shall be grounded to the vehicle metal structure and this ground shall normally be considered the second conductor of the circuit. An additional separate ground cable to the chassis or negative bus bar is recommended for large electrical loads.​

    Section 7 of this document is interesting as well. This too.
    Last edited: Sep 27, 2019
  5. KF5LJW

    KF5LJW Ham Member QRZ Page

    I like the second link as it goes into some detail, but still fails to point directly what the issue really is and just how dangerous it is. Not to mention all that noise you have willingly asked and invited into your radio to make themselves at home.

    Now if some of you are still on the fence just go back to post 22 diagram and look real close at the drawings especially the two lower drawings with Negative terminated directly to the Battery Negative Term Post. So here is the problem. As most of you know a vehicles uses the chassis for the negative conductor. That is accomplished with the factor Bonding Jumper between the Battery Negative Term Post and the vehicle Chassis usually on the wheel well or firewall. Easy to see and locate. Every last pico-Amp of the vehicles current flows through that cable. All of it. Starter, lights, horn, power seats/door/locks, ECM, electronis, navigation, entertainment, cameras, all of it.

    When you terminate on the Battery Negative Term Post, YOU HAVE installed a parallel Bonding Jumper. Look, it is right in front of you screaming for your attention. Look at it, the bonding jumper route is the black negative radio conductor and your coax shield, and possible less likely is the metallic radio case if bolted into place to chassis. Long jumper, but it is directly in parallel with the vehicle Bonding Jumper. Not an opinion, just a fact.

    That means your radio is being used as a circuit conductor for all vehicle current flowing on the Negative only. How much current may shock some of you. Roughly 10:1. For every 10-amps, about 1 amp through your radio which is pure noise voltage and current. Not an opinion, just fact of Parallel Circuit Laws. you can see and test for yourselves. Ladies and gentle this is the Mother of GROUND LOOPS, the worse you can create. OK so under normal operation you get away with it albeit poorly and noisier than it has to be.

    Do you have any issues with running 20 to 40 amps through your coax and radio wiring every time you start the car? Again just a fact with a current ratio of 10:1. Your starter will draw 200 and a lot more amps the larger the engine gets. About 10% will flow through your negative and coax shield.

    Here is where it gets real fun and educational this fool learned 40 years ago when he started his career. If anything happens to the factory Bonding Jumper, that now leaves your radio as the only Bonding Jumper and you will discover it when you go to start your engine and smoke fills the cabin. You will find your coax and negative radio wire smoked. Good thing you listened to some Alien and used that fuse on the negative.

    Want to do it correctly and avoid all that crap you have been filled with? LOSE the FUSE and USE the CHASSIS for the Negative as close to the radio as possible. Vehicles are full of chassis hard points made to do exactly that. Look close and you will find ground terminals the factory uses for things like power/heated seats, windows. ECM under some seats. Seat bolts are good.

    Not only is that the best practice in terms of performance and safety, but also the least expensive and easiest method you can use. It does not get any better than Win Win.

    In some rare cases like EV's or chassis os some vehicle does not make low resistance connection, then you can run Negative to the engine compartment. Understand doing so runs the risk of picking up noise from vehicle wiring, so keep radio power wiring segregated from vehicle wiring crossing at right angles when possible. DO NOT TERMINATE Negative from radio to battery post. Terminate on top of the Ring Terminal on the other end of the factory Bonding Jumper on the chassis. Do not put your ring terminal under factory ring terminal. Radio goes on top to prevent auto starting current to have to flow through your terminal. Use external Dragon Tooth locking hardware with anti-oxident.
    Last edited: Sep 27, 2019
    AI7PM likes this.
  6. W5GX

    W5GX Ham Member QRZ Page

    Sure does - I figured that's where you were going with it. Thanks.

    Takes me back to my car stereo enthusiasm days - short ground wires for the amps. At least it seems consistent.
  7. W5GX

    W5GX Ham Member QRZ Page

    Maybe a "not so dangerous" experiment - at least when it comes to the asset protection of your radio:

    1. Disconnect radio altogether so it is not attached to the 12V system.
    2. Disconnect main ground wire from battery and chassis.
    3. Run 10, 12, or so, gauge wire from battery negative to chassis.
    4. Crank engine.
    5. Watch the sparks fly!

    That's what your radio negative wire and coax ground are, if you go straight to battery.

    Do not attempt unless you're willing to vaporize insulation and/or the wire it's wrapped around.
  8. KF5LJW

    KF5LJW Ham Member QRZ Page

    You are welcome and thanks for your time.

    You hit the nail on the head. Exact same reasons apply . Going to the Chassis does two things you want. Makes it safe, and minimizes noise affording the best method possible. Only improvement you can makes is turn the engine and ignition off. Do you recall seeing some Audio Enthusiast that ran so much power the headlights are modulated by the audio? That audio voltage would be riding on top of the DC on your ground.

    Having said all that, there are some rare applications where you want to connect Negative to the Battery Term Post. However there are a couple of conditions that must be met:

    1. The equipment MUST HAVE a FLOATING SYSTEM which means Negative is not referenced to Chassis, or not a Grounded System where one circuit conductor is Bonded to Ground. Example of another Grounded System is your house electrical system where one circuit conductor is referenced to Ground aka Neutral Conductor.

    2. Both Polarities MUST BE FUSED on a FLOATING SYSTEM.

    3. Although not a mandatory requirement, more like a justification, the equipment uses a lot of power. Your radio does not fit that requirement. I can only think of two pieces of equipment that fit the above. An Inverter or a winch. But Even an Inverter or Winch may or may not have a Floating Negative. I do not know of any amateur mobile radios that have a Floating Negative, only 1 or 2 commercial radios do that.

    So I hope this has helped many of you, and now you understand what is going on. So the next time an alien or someone shows up pretending to know what they are talking about, advocates connecting the radio negative directly to the battery term post. Shoot them down because they do not have your best interest in mind, telling you how to destroy your radio, and compromise the normal performance. It is basic Parallel Circuit Laws that cannot be disputed unless you have no clue what you are talking about.
  9. W5GX

    W5GX Ham Member QRZ Page

    KB0MNM and AK5B like this.
  10. KB0MNM

    KB0MNM Ham Member QRZ Page

    B.T.W.- Home-built brute-force filter: As others have said, this should only be considered as a *possible* additional expense. Not *every* radio installation should need a powerline filter, that can be determined in one of two ways: 1. Measure the incoming alternator or other noise ripple with an oscilloscope or better TRMS multimeter while running the engine speed up and down. 2. Wait until you or other folks note a 'whirring' noise on your audio that seems to vary with engine speed. The entry of this noise may not be on the power supply leads- it could be at the receiver or your antenna during transmit. If it is still present in receive with the antenna lead disconnected, there are two remedies: 1. Install a brute force filter. 2. Replace a few parts ( usually larger electrolytic capacitors ) in your radio power supply section- newer radios seldom need or benefit from this. BTW- The Yaesu external speaker listed above has been discontinued ( SP-4, I think ). The replacement for it is a 4 ohm speaker, which should work- yet does not have the filter as a switchable item. Timewave ( ) and others make DSP-corrected external speakers, yet the price may be a bit steep.

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