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Discussion Starter #1
Is the battery on the '04 K12GT grounded to the chassis? If so, where? Is it easily accessible? Thx
 

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Absolutely it's grounded. Just follow the ground lead from the battery. Is it easy to get at? At the batter, yes. At the other end, no. What is the issue or modification you are addressing?

GTRider
 

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Two grounds from the battery, one goes toward the front and disappears.....the other one goes to the starter and from there also goes to the frame with a smaller wire. Not easy to see but if you remove the rail that holds the fuses you should have access to it.


Here is a pic where you can see the smaller ground wire and I think the larger one removed from the starter bracket. Starter is a little sideways.....I was working on a procedure to remove it without taking the tranny out.

But if you want to remove the ground at the starter you will need a long ball end wrench. :)

 

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Discussion Starter #4
GTRider said:
Absolutely it's grounded. Just follow the ground lead from the battery. Is it easy to get at? At the batter, yes. At the other end, no. What is the issue or modification you are addressing?

GTRider
In addition to being an avid BMW rider (10K shy of 200K) I am also a licensed Ham radio operator. I combined my two hobbies by installing a Ham radio on my GT. The issue is alternator whine. The communication farkles (Amp, AutoCom, Zumo) are connected to a fuse panel. The Ham radio is connected to an inline noise filter then to the battery. A relay provides on/off operation. Despite bypassing the ignition, I am still picking up and transmitting alternator whine. A contributing factor may be a ground loop caused by multiple ground points. If I ground the radio and antenna to the same ground point as the battery, maybe I could eliminate the ground loop and minimize the noise.
 

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Discussion Starter #5
H96669 said:
Two grounds from the battery, one goes toward the front and disappears.....the other one goes to the starter and from there also goes to the frame with a smaller wire. Not easy to see but if you remove the rail that holds the fuses you should have access to it.


Here is a pic where you can see the smaller ground wire and I think the larger one removed from the starter bracket. Starter is a little sideways.....I was working on a procedure to remove it without taking the tranny out.

But if you want to remove the ground at the starter you will need a long ball end wrench. :)

Thank you. This is exactly what I am looking for. I am trying to eliminate a ground loop that may be contributing to the alternator whine I am transmitting from my Ham radio. If I can ground both the radio and the antenna to the same point on the frame as the battery, maybe I can minimize the ground loop that is causing my headaches. Any other recommendations are greatly appreciated. Cheers
 

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Being a voluntarily expired G8 myself, I'd say with all the push from the alternator running the bike, rfi and ground loops will always be a problem.

So why not think about using a switcher psu for your gear, then you will be totally isolated galvanically so to speak, except on the rf antenna ground plane? Of course you need to be careful that all your cases etc are connected to the virtual ground side of the SMPS source.

If you are still getting alternator pickup, then that must be radiated and a bigger challenge to fix with screening, baluns and balanced antennas. Try floating the rig first running off a mains psu and see what you get. If rfi then it must be air borne, not from ground loops.

73's - Vox



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Discussion Starter #7
voxmagna said:
Being a voluntarily expired G8 myself, I'd say with all the push from the alternator running the bike, rfi and ground loops will always be a problem.

So why not think about using a switcher psu for your gear, then you will be totally isolated galvanically so to speak, except on the rf antenna ground plane? Of course you need to be careful that all your cases etc are connected to the virtual ground side of the SMPS source.

If you are still getting alternator pickup, then that must be radiated and a bigger challenge to fix with screening, baluns and balanced antennas. Try floating the rig first running off a mains psu and see what you get. If rfi then it must be air borne, not from ground loops.

73's - Vox
If by SMPS source you are referring to the battery, then I have already isolated my rig. The communication components (Amp, AutoCom, Zumo/XM) are connected to a fuse panel, which is powered by the battery. The HT's power adapter is directly connected to the battery, with a 20amp DC inline noise filter in-between. However, the multiple ground points (fuse panel to the battery, battery to the chassis, etc.) may be creating a groung loop, which may be contributing to the alternator whine I am transmitting. I agree with your assertion that radiation may be picked up by other sources, such as the AutoCom. However, when I am just listening to the Zumo/XM through the AutoCom (with the HT off) the signal is crisp and clean. So, the HT is picking something up, but I don't know where. Everything I read suggests ground loop. Any recommendations are greatly appreciated.
 

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By SMPS source I mean that the only wiring between the bike and your kit is between the bike's battery and an SMPS dc-dc converter 16-12 volt if that's what your kit runs on. If they put your kit in metal boxes and ground the chassis, then you make sure they are isolated from anything metal (ground) on the bike and rf decoupled with capacitors.

The only place where you need to use the bike metal work as a ground is the antenna. If they are mag mounts then they may already be fully isolated with internal baluns, or unblanced and capacitively coupled to the ground plane, if they are not then you can isolate the screen with capacitors.

In other words, if you measure the high ohm resistance between any part of your comms kit - metalwork, connectors, antennae, - there will be no resistance reading to the bike frame or battery, therefore no ac/dc ground loops.

All stock stuff for hams running mobile rigs.

As for rfi, after eliminating for ground paths or testing with a mains supply and kit isolated from the bike, you just need to break out wifeys aluminium kitchen foil and do some experiments.

The furthest most go will be adding audio kit to bikes, so I would be surprised if you will get quality replies covering tx/rx comms installations. In the past I've found no two installations and problems require the same solution. A lot has to do with understanding interference and some of it is 'Black Art' and not science that can be answered easily in a few posts.



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