Noise on AM channels, ground loop? (1 Viewer)

[RavenTai]

I have had bad noise on AM channels and poor reception since I got my cruiser, this is one place my Chevy was nicer, on clear nights I could get Texas, Louisiana and sometimes Chicago stations when in central Florida or GA and could pick up Atlanta stations anywhere in GA any time of day. In the cruiser I can only get local stations.

The noise goes away when I shut the engine off but there is still a lot of static, the noise is a pulsing wine that goes up and down in pitch but does not follow RPM it also seams louder at idle.

I have tried loosening and tightening the top “nut” on the antenna as per one of the TSB’s although it was loose tightening it made no improvement.

This weekend I started on my dual battery setup, the ice storm set me back and did not get started until mid Sunday, I was still working on it Monday morning before work and did not have a ground from the battery to the body, just the main 1/0 cable to the block, body loads (like the radio) would have to get to the block via the bonding straps on the engine. On the way to work the noise and most of the static was gone it sounded as good as AM gets, Tuesday morning I put a 1/0 ground from the block to the frame. Now the noise is back

I am wondering if I have a ground loop problem? On the left side of the motor is a group of grounding wires that travel between the block body and frame all these wires pass close to the coil wire distributor and alternator. Perhaps without another ground to play against of they did not pick up noise?

I am thinking about removing those and having a single ground point on the passenger side that ties the block frame and body together, but it seams Toyota put them there for a reason? Short return path for ignition current?

I am using OEM plugs wires cap and rotor.

 

[CDN_Cruiser]

Raven:

I don't know a ton about this, but it is quite common and recommended to have a ground bus connected to a common RF ground point for radios - so this may do the trick.

Cheers, Hugh

 

[IdahoDoug]

Speak English for us wiring-impaired types. My 97 also does this engine RPM static on AM and I listen to a lot of talk radio. What's this bus thing and all??

DougM

 

[CDN_Cruiser]

Sorry - plain language has a lot going for it

When you are wiring radios, you typically wire all of the radios to a common ground point (e.g., a busbar - like a fuse block) and then wire this common ground point using one large wire to ground (in this case the chassis). Ideally, the ground runs should be as short as possible - basically, for radio frequency (RF) grounding, you want to ground everything to a common point with the shortest possible path.

Longer wires (ground, power, etc) can effectively act as an antenna and pick-up noise. Similarly, as with all wiring, poor antenna connections, poor quality antenna line, etc can also allow noise to leak into the system.

I'm not sure if this is the problem or not, but based on Raven's experience it may help.

The other thing you could look into is go to a radio store (ideally someone that sells amateur radios, but CB shops will have these as well) and ask them about filters (IIRC you would want a 'high pass filter') that can be helpful in reducing problems.

Cheers, Hugh

 

[RavenTai]

Thanks Hugh, I am going to give it a try and see what happens.

I am not good with RF, can’t measure it, can’t think about it, and can’t predict it.

 

[Pskhaat]

Raven, on the cable to the antenna, you can take the `ground' side and at the antenna and put a small wire to the nearby body. The antenna will need a good counterpoise (ground) and the body is for a verticle antenna like that. I don't remember how the 80 works with the motorized antenna and it's through-hold on the body panel, but still...ground to the body.

After that, you (as earlier suggested) should try some filters.

 

[RavenTai]

Raven, on the cable to the antenna, you can take the `ground' side and at the antenna and put a small wire to the nearby body. The antenna will need a good counterpoise (ground) and the body is for a verticle antenna like that. I don't remember how the 80 works with the motorized antenna and it's through-hold on the body panel, but still...ground to the body.

After that, you (as earlier suggested) should try some filters.

Checking/improving the antenna ground sounds like a good thing to do also, after removing all the outside the fender parts of the antenna everything looked good. Maybe I should pull it out all the way take a look.

For the antenna is it more important to ground to the fender surrounding it (ground plane?) than to a central grounding point for the electrical system?

These filters you guys are talking about do they go in series on the power leading to the radio or can they dampen the entire electrical system? And why high pass? I would think I would want them to stop high frequency ripple/noise in the +/- supplied to the radio? Not pass it on?

I have a 16V 1/4 farad capacitor (yes it is big, size of a coke can) that I was planning to put on the second fuse box to take out most of the ripple there, later on all the audio devices (Stereo. CB, Carputer) will get there power there, I am thinking this may have some effect on the rest of the system also as it will be in parallel with everything, but I have read the longer the wires between the cap and a device the less the effect. So it may just have any effect on stuff getting power directly from the aux fuse box

Also used to be alternators had a small cap on their output to reduce their noise (my 81 Datson 280ZX had these) thinking about putting one on the alternator output figure it cannot hurt,

 

[Pskhaat]

I would say yes to the grounding on the fender where the antenna is. DC and AC `ground' are very different, especially in an RF sense.

They are small and go in series with the radio. I am sure there are others that do the whole electrical system. Low broadcast AM band is about 530000 Hz (broadcast FM significantly higher), while RPM of the alternator and frequency of the coil is significantly lower, so you would want a high-pass filter.

 

[ogsuv]

I concur on the grounding at the fender. An easy way to cheat is to take a jumper from the radio ground wire strip back an inch or so and slide it into the antenna connection, outside shield only.

Works about 50% of the time, and easy to try. Just a thought..........

 

[Pskhaat]

ogsuv, where in Mad town are you? My wife's from Stoughton and we're back in that area often.

 

[ogsuv]

Sun Prairie, so very close. Small world.

 

[RavenTai]

hmm found this looking for something else,

sounds like my symptoms match well to fuel pump or computer noise, need some ferite beads

http://www.arrl.org/tis/info/fuel.html

Doug yours shoudl be alternator or ignition related

 

[Pskhaat]

ARRL would certainly know what they were talking about!