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Discussion Starter · #1 ·
Not sure if the answer to this is obvious, but I don't really have any experience dealing with audio systems so I can't be too sure. I keep having this weird problem where the sound from the FM radio will come in PERFECTLY when I come to a stop, but starts to break up or sound muffled whenever I start moving. When I first got the van a few months back, I mostly ignored this because the stock speakers were so blown out that I almost never listened to the radio. But now that I've got some decent plug-and-play speakers in it, the interference is impossible to ignore. I had purchased a new head unit to go along with the new speakers, so I switched back and forth between the new and the old one to see if it made any sort of difference. Nothing. On both, it does the exact same thing.

Like I said before, this problem was present before I installed the new speakers, it's just really pronounced now due to the fact that the new ones are of a higher quality than the OEMs. I've had a few people tell me that this could be due to alternator interference, but the problem happens whether I'm going 15 or 50 MPH, with and without any significant electrical loads. If I'm sitting still, it doesn't matter how many other electrical loads are there, it sounds great. The second I start moving, it goes back to sounding horrible. Sometimes it makes the station sound like I have the treble turned all the way down, other times the signal will come in fine but will break up constantly, like I'm getting out of range. Not too sure what direction I want to go from here, I don't want to just start throwing parts at it. If anyone here has had a similar problem and has a story about what fixed it, I'd love to hear it.

Thanks
 

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Discussion Starter · #5 ·
How does it do if you disconnect the alternator?
Not sure, haven’t tried that yet. When I get some free time here soon I’ll disconnect it. I might as well, it can’t hurt to check. I just don’t get why it’s happening with a seemingly bone stock setup. I know it was owned by the fire department before, and they left a bunch of loose, large gauge electrical wires all over the inside and under the hood. But they don’t go to anything anymore, at least nothing that I can find. There are some thick cables that lead up behind the headliner, probably went to antennas at one point. ButI don’t see how they could be powered, there’s no connection at the battery and no ground that I can spot
 

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01 Astro RWD Cargo, 97 AWD Mark III
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Sounds like the ground got messed up. Run a new ground to the head unit and see if it makes any difference.
 
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1998 LS AWD Forest Green metallic
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How does it do if you disconnect the alternator?
I know nothing of you location or surroundings, but my first thought is this sounds like a classic of reflected signals, off buildings etc.
In my shop area, I often listen to a somewhat local FM radio station. The signal fades out and returns depending upon where I stand in the room, relative to the radio receiver.
It a reflection ( from my body) arrives timed exactly 108 degrees out of phase, it may cancel the desired signal, or at least partially cancel it.
Old TV's with outdoor antennas in somewhat rural areas used to suffer from "Ghosts". That was a shaddow of the main image, caused by reflections of the desired signal off large builings, farm silos, or potentially even rocky faces of nearby hills or mountains.
How far are you from the transmitting antenna?
Is it mainly just this one station, or do most other stations exhibit the same symptoms?

Tune in the desired station and park the van with the volume turned up so you can hear the audio from outside the van. The start walking around the van in the vicinity of the antenna, and listen for similar type of interference. As little as three to six feet away may be enough to simulate the situation.
I may be way off base, but this is a type of interfference that most people have no experience with.
If that is what you are experiencing, the fading reception is likely caused by reflations as you change locations relative to the station antenna and local structures.
There is a ham radio term for a rapid sequence of that phenomenon. It is called 'picket fencing' and it sounds as if the signal was be cancelled by each slat of a picket fence, if you were driving past it at speed.
Rod Johnson
Issaquah, WA
 

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Discussion Starter · #9 ·
I know nothing of you location or surroundings, but my first thought is this sounds like a classic of reflected signals, off buildings etc.
In my shop area, I often listen to a somewhat local FM radio station. The signal fades out and returns depending upon where I stand in the room, relative to the radio receiver.
It a reflection ( from my body) arrives timed exactly 108 degrees out of phase, it may cancel the desired signal, or at least partially cancel it.
Old TV's with outdoor antennas in somewhat rural areas used to suffer from "Ghosts". That was a shaddow of the main image, caused by reflections of the desired signal off large builings, farm silos, or potentially even rocky faces of nearby hills or mountains.
How far are you from the transmitting antenna?
Is it mainly just this one station, or do most other stations exhibit the same symptoms?

Tune in the desired station and park the van with the volume turned up so you can hear the audio from outside the van. The start walking around the van in the vicinity of the antenna, and listen for similar type of interference. As little as three to six feet away may be enough to simulate the situation.
I may be way off base, but this is a type of interfference that most people have no experience with.
If that is what you are experiencing, the fading reception is likely caused by reflations as you change locations relative to the station antenna and local structures.
There is a ham radio term for a rapid sequence of that phenomenon. It is called 'picket fencing' and it sounds as if the signal was be cancelled by each slat of a picket fence, if you were driving past it at speed.
Rod Johnson
Issaquah, WA
This is a pretty interesting theory. I’ve never heard of it before, but it does make sense. I’m not entirely sure it’s the issue though, since almost all of the stations are the high-strength Portland ones and I’m less than 10 miles across the river. But some stations are worse than others, so it’s worth a try. That might also explain why it always gets consistently worse in certain areas
 

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Discussion Starter · #10 ·
Also, don't under estimate wires that don't go anywhere in this scenario. Those are often called antennas.
But could they still be causing interference even if they’re not powered? I think all of that was disconnected when it was decommissioned. It might be possible that they were spliced into a pre existing wiring line and made to look OEM, but I kind of doubt it. The shoddy aftermarket wiring these guys did mostly stands out like a sore thumb. I’ll take a look under the hood and re examine all the lines coming off the positive terminal just to be safe though
 

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Discussion Starter · #11 ·
Sounds like the ground got messed up. Run a new ground to the head unit and see if it makes any difference.
Is the ground line that runs to the head unit that difficult to backtrack? If it’s easy to get at, I might take some of the interior panels off and see if I can spot anything weird. I heard a story on another post about a guy whose ground was acting like an antenna, do you think that’s possible here?
 

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It does not have to be weak signals. In fact reflected signals from strong stations may be stronger and can interfere more easily.
W ham radio operators can bounce (using directional antennas) signals off Mt. Rainier regularly. They can be picked up from most places than can 'see' the mountain, from ccentral Oregon to BC. We also use the Olympic mountain range.

Re: Picket fencing, for reference and education.
It may not be related to your specific problem, but worth the read.
"picket fencing" link:
Guide To Good Reception

Rod J
Issaquah WA
 

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Discussion Starter · #13 ·
It does not have to be weak signals. In fact reflected signals from strong stations may be stronger and can interfere more easily.
W ham radio operators can bounce (using directional antennas) signals off Mt. Rainier regularly. They can be picked up from most places than can 'see' the mountain, from ccentral Oregon to BC. We also use the Olympic mountain range.

Re: Picket fencing, for reference and education.
It may not be related to your specific problem, but worth the read.
"picket fencing" link:
Guide To Good Reception

Rod J
Issaquah WA
Def worth a read, thanks for the tip. I'll try out some of the troubleshooting steps pretty soon here
 

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BAD ANTENNA... or BAD antenna connector.
(one of the few things you didn't change common to both radios)
Also assuming you are running the factory stock antenna?
 

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Discussion Starter · #17 ·
BAD ANTENNA... or BAD antenna connector.
(one of the few things you didn't change common to both radios)
Also assuming you are running the factory stock antenna?
Yeah, it’s the stock antenna. Although I don’t know if it was touched in any way by the guys who ran the other wires throughout the van. They could have tapped into it or the radio ground at some point
 

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Discussion Starter · #19 ·
Find the radio ground in the wiring harness. Run a Heavy wire from there to a chassis ground. Miss the harness and the tiny antenna/wire it uses.
I’ll try that out this weekend, it seems like a lot of the suggestions are about the radio ground. At least it’s easy enough to access all of that once the head unit is removed
 

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Messing with grounds won't fix it if you have an issue with antenna or connector... which I would check first.
One easy test: Do you get AM reception?
If so then the antenna and cable is probably ok.
Have fun.. good luck
 
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