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Author Topic: Run Negative to battery or Ground the negative at the radio in 2010 GMC ?  (Read 5472 times)
KG5KS
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« on: November 18, 2010, 05:49:04 PM »

I have always ran both negative and positive wires straight to the battery.  However when installing audio amplifiers would always run a short negative to chassis ground.  Never a ground loop problem that way.  However just bought a new 2010 GMC Sierra SLE 4x4 Crew truck and was told it either had 23 or 26 seperate computers in it ..yuck.  Decided to run + - wires from aux battery under the truck and place remote radio under the back seat and the remote head /s in the front keeping the coax at back of the cab.  So just wondering if to run negative wire all the way or simply drill a hole and ground it at the radio ?

I will be running 8 gauge wire and might put in a small amp or run an Kenwood TS-480 HX 200 watt rig, Kenwood D710A vhf/uhf, Digital tnc, laptop or netbook will be working digital and voice .

Would like to hear also from anyone who has installed a radio system in 2010 Chevy / GMC Sierra Crew.

Thank you
73
Kenny
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K5LXP
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« Reply #1 on: November 18, 2010, 08:11:36 PM »


<http://www.eham.net/ehamforum/smf/index.php/topic,71001.0.html>


Mark K5LXP
Albuquerque, NM
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KB1LKR
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« Reply #2 on: November 18, 2010, 08:20:31 PM »

See: http://service.gm.com/techlineinfo/radio.html


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K0BG
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« Reply #3 on: November 19, 2010, 06:31:23 AM »

There is a difference in opinions about where to hook the negative lead; directly at the battery, or at the battery's chassis grounding point. There are fine points for each selection. You sure don't want to do the latter if you're running high power (≈500 watts).

All said and done, every single automobile manufacturer, except one (and only in a select few models) recommend direct connections to the battery. Fused correctly, of course.

The radio itself is already DC ground through it power cable. If you have to run a separate ground from the radio to the chassis to correct some sort of RFI problem, then something else in the installation is amiss. Typically, that's a ground loop.

And, wherever you mount the antenna (I assume the bed), make sure you bond the bed on all four corners, as well as to the cab. If you don't, you will have RFI problems.
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W8JX
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« Reply #4 on: November 19, 2010, 06:40:19 AM »

Running power legs back to battery is still a good idea. You might consider using a RF filter choke in power supply leg to as it can prevent RFI coming into radio via power leg and also coming from radio to cars electronics. I always ground radio chassis to body as well.
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K0BG
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« Reply #5 on: November 19, 2010, 10:57:16 AM »

Ah! There's another common misconception between common mode current and differential mode current, and when to, and when not to, filter!

About all a brute force filter will do is increase the voltage drop, usually by a volt or more. Yes, it just might put a bandaid on alternator whine, but 99% of the time, that's caused by a ground loop. If you use adequately sized wire to minimize voltage drop to less than .5 volts, any filter you install will have almost zero effect, except for voltage drop.
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W8JX
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« Reply #6 on: November 19, 2010, 02:13:25 PM »

I have used filter choke in mobile HF through UHF radio for over 20 years and will continue to do so and I have not seen the voltage drop you suggest but it has cleaned up whine and hash that would come up power leg without it. I also use 80 to 100, 000 ufd Electrolitic cap in parallel after choke near radio and it lowers average voltage drop and reduces peak load on car because while without cap draw can swing from 3 to 20 amps plus talking and with cap it averages about 8 or so as cap feed peaks and recharge during zero modulation and it works pretty sweet.   
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K0BG
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« Reply #7 on: November 19, 2010, 02:47:57 PM »

John, I have a whole new outlook on that, and perhaps we should talk on the phone.

Brute force filters are patches, not repairs or fixes as it were. Almost without exception, RFI, ground loops, and inductive coupling interference is a result of incorrect installation parameters. You cannot believe some of the photo that are sent to me for inclusion in my web site's Photo Gallery. No darn wonder folks have alternator whine, and other maladies.

The real facts are, if you install radio gear correctly, you don't need filters, big huge caps, and other patches to fix RFI problems, because you won't have any to start with. Mark, K5LXP, has a whole lot of experience in installing radio gear, as I have. I can't speak for him directly, but he doesn't believe in patches either. We agree on drilling the proper holes, and when you do, you just do not have alternator whine problems.

Every HF mobile installation will have some level of common mode current, if for no other reason than ground loss. The antenna return current has to flow back to the source, and if there is excessive ground loss, that's through the coax cable, and antenna control leads. Proper choking takes care of most of the problem, but when antennas aren't mounted securely, the problem is exacerbated. I've seen cases where the common mode over the coax exceeds one amp. Gee! There's only 1.4 amps flowing into 50 Ω load at 100 watts. If you think about it, you'll get the picture. Sure, you can patch is, but that does not fix the problem.

Wiring is another area where folks just don't get the picture. The key here is to keep the impedance of the wiring as low as you can. Using the rule a thumb about keeping the voltage drop under .5 volts, suffices most of the time. When it doesn't, you can patch it with a filter. It's still there, you just don't notice it. If you indeed need to rely on an inline filter to fix an RFI problem, you would be better off labor and monies wise, to fix rather than patch.

And lets address the Farad cap issue. Personally, I'm scared of them. I have seen the damage they can do when they let loose. There are several ways to do it. Most are rated at 20 vdc, and they're on the ragged edge then. If you jump start a vehicle with a booster-starter unit, you run a very good chance of ungluing one. Or, short one out. If you think an SLI battery will get nasty under a dead short, you ought to see a 1 or 2 Farad cap let loose. As a side light... I have a good friend who is in the car stereo business. On the wall of his office, is a photo of a 2008 Porsche 911 which looks ike Al-Qaeda blew it up. What actually happened was, a 5 Farad cap was shorted out, by all things, a golf club. It isn't a pretty picture.

You can do your thing, and that's fine. But for me, I'm a little more careful.
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W8JX
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« Reply #8 on: November 19, 2010, 05:55:40 PM »

The problem is that a car is not "mil spec". I worked in R&D in flight test for many years and aircraft systems and sub systems are designed to suppress their own interference but not so in a car. Basically a Detroit car today is kinda the sum of parts from lowest bidder and lacks refinement in noise and RF suppression. Not sure why you are being stubborn about using a filter choke. While it is try that some radios have better internal filtering and suppression on power leg than others there is nothing wrong with a little insurance and some external brute force help.  I remember back in 90 or 91 there was issue with VHF/UHF Camarys causing onboard computer failure caused by a loop back through power leg. I bought a new 91 then and installed a 50 watt mobile and powered it thru a filter choke too and never had a problem.
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K0BG
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« Reply #9 on: November 19, 2010, 06:50:37 PM »

John, I guess I'm lost.

Mil Spec doesn't compute when it comes to automotive applications. And, the fact you worked with R&D in the aircraft industry doesn't compute either. Further, I don't understand about suppression on the "power" leg. In any case, I'm not dead set against using a power line filters, but in an HF mobile scenario, there is no reason to do so if you do the other necessary requirements. That is, if you do the installation correctly as I have outlined. Lastly, your explanation about the power amplifier installation doesn't make sense either. Unless of course, there was a problem with common mode.

Let's revisit the Camry issue too. Back in the early 90s, Toyota had a problem with engine CPUs in several of their models, including the Camry. The issue had nothing to do with RFI, common mode current, or anything related to amateur radio, CB radio, or any other radio service issue. After a lot of investigation by Toyota, and the NHTSA, this issue was solved by replacing a faulty sensor on the cam shaft. There was never any connection to RFI from any source.
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W8JX
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« Reply #10 on: November 19, 2010, 08:31:46 PM »

The point I was making with mil spec is that other poster was over complicating issue and solutions. (kinda like mil specs are) When you install and power a HF radio in car its power leg can become a source for noise input for car generated RFI and potentially act as a counter poise of sorts and induce RF current on power leg into car.

Interesting comment on Toyota problem. At time they told me I could void my warranty if installed radio but did anyway and never had a problem or any engine related problem in the 12 years and 230,000 miles I drove the car
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K0BG
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« Reply #11 on: November 20, 2010, 06:39:59 AM »

John, it is almost impossible to have RF imposed on DC power cables. You could, under the right conditions (poor installation practices), to have a high enough level of common mode where is might cause a problem. And if there was, a brute force filter isn't going to help.

Almost all RFI problems are caused by common mode, typically on the coax, but on antenna control cables as well. As I said before, you can't believe some of the things folks do when they install radio gear in their vehicles. Based solely on the e-mails I get, I guess I shouldn't be surprised.
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W8JX
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« Reply #12 on: November 20, 2010, 09:23:05 AM »

John, it is almost impossible to have RF imposed on DC power cables. You could, under the right conditions (poor installation practices), to have a high enough level of common mode where is might cause a problem. And if there was, a brute force filter isn't going to help.

Not impossible at all and length and location play a roll here. As far a brute force filter is is not hard RF in filter.


Almost all RFI problems are caused by common mode, typically on the coax, but on antenna control cables as well. As I said before, you can't believe some of the things folks do when they install radio gear in their vehicles. Based solely on the e-mails I get, I guess I shouldn't be surprised.

When RF problems are coax related is is because of unbalanced loads that cause current nodes or radio to also seek another path and RFI problems and proper shielding of coax and control cables can help. I do not HF mobile much these days but have a lot in past and always used brute force, large CAP's to soften average current draw, grounded radio and antenna to chassis and frame and never had any problems. (I also used a separate battery in car to power HF radio that I could isolate for extended use with vehicle off and not worry about it starting. When operating like this the CAP's helped a lot because you got good radio performance done to a nearly dead battery.
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K0BG
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« Reply #13 on: November 20, 2010, 10:26:25 AM »

It may be a rude awakening, but every HF mobile has some common mode. Whether is causes any known problem is moot. The issue with common mode in an HF mobile is directly related to the ground losses present, and they are never zero! Since it is a two way street, and late model vehicles are awash with internal RFI, if you don't take care of the common mode, the receive noise level can be almost deafening.
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KG5KS
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« Reply #14 on: November 20, 2010, 08:27:44 PM »

Appreciate those replies.  Guess will continue running both + - wires directly to battery.  Looks like # 8 is what I will be using for both and fusing both at battery.  Looks like Kenwood D 710A for VHF / UHF and Kenwood TS-480 for HF, with wires running on drivers side and NMO mount on top of cab for VHF / UHF and Screwdriver type antenna on top, back bumper "drivers side".  Guess 8X coax for HF antenna.

Appreciate it.

Thank you

Kenny

ARS KG5KS
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