Radio/Electronics Specialists Needed

94GTLaserRC · Nov 20, 2008

BACKGROUND INFO: Ive been having some issues with reception with the Sony XPlod. I new the stud was broken for the antenna inside the antenna base, so I replaced the base. When I removed the antenna wire from the stereo to inspect everything, I noticed that the antenna wire was cut and mended after it exits the stereo but before it connects to the antenna base wire---which connects behind the glove box...

I took the tape off and noticed that the single wire was soldered and the outside sheathing was twisted around to mend it. (The only one who touched anything in there was Circuit City when they installed the harness...I think they cut it and mended it).

Anyway, I resoldered it really well and tried the unit before installing it...it seemed to get good reception. When I start the car however, the reception is very poor.

MAIN QUESTION. What would cause the reception to be fairly good with Key on, Engine off, but lose recpetion when engine is running. Is it related to the 'mending' of the antenna wire? Would a FULL new cable resove this?
I need to find the cables to connect everything without attachments.

Thanks
RC

Badloser · Nov 20, 2008

something might be loose like a wire that they did not connect correctly.

94GTLaserRC · Nov 21, 2008

Badloser said:
something might be loose like a wire that they did not connect correctly.

I should point out that the only thing that happens with car running is worse reception. I do not "HEAR" any engine noises or other strange noises through the speakers...just decreased reception. Any thoughts?
RC

hollywoodstang · Nov 21, 2008

RC you get up really early don't you? It's 4 am in the morning here in L.A. Do you ever take break from working on your mustang? and perhaps go "FISHING"?

Well good luck with your new problem Mr. king of bling

94GTLaserRC · Nov 21, 2008

hollywoodstang said:
RC you get up really early don't you? It's 4 am in the morning here in L.A. Do you ever take break from working on your mustang? and perhaps go "FISHING"?

Well good luck with your new problem Mr. king of bling

I ALWAYS take some breaks from working on it, but NEVER stop "THINKING" about my next move! ....Thanks for the free bump
RC

j_lutter31 · Nov 21, 2008

My guess would be that a good antenna wire shields itself from engine interference, when the wire was cut and soldered it lost the proper insulation it needs to shield out the interference, thus losing all reception with the engine running....I'm assuming you just wrapped it with electrical tape......But still know that I am just throwing a guess out there.....

94GTLaserRC · Nov 21, 2008

j_lutter31 said:
My guess would be that a good antenna wire shields itself from engine interference, when the wire was cut and soldered it lost the proper insulation it needs to shield out the interference, thus losing all reception with the engine running....I'm assuming you just wrapped it with electrical tape......But still know that I am just throwing a guess out there.....

I think Circuit City Cut it and YES, it was wrapped with electric tape. The single center wire was soldered. The outside metal wiring that surrounds it was "wound" together then the whole thing was wrapped with electric tape.

Any other thoughts?
RC

mhespenh · Nov 22, 2008

94GTLaserRC said:
I think Circuit City Cut it and YES, it was wrapped with electric tape. The single center wire was soldered. The outside metal wiring that surrounds it was "wound" together then the whole thing was wrapped with electric tape.

Any other thoughts?
RC

I think that the woven insulators are intended to work like a Faraday cage (Faraday Cage - Wikipedia, the free encyclopedia), but must be connected- that is to say, when it was cut and "woven" back together the original pathways were broken, thus ruining its anti-interference powers. The reason it is worse when your car is on, is because of all the electromagnetic waves the various parts of your car put out when on (alternator, ignition system, spark plugs, etc). I'd try a new cable, hell, if it doesn't work you can always return it

-Michael (computer engineering student- but our sister major is electrical engineering, so its close )

*EDIT* Upon further reading, the antenna cable is essentially a coax cable which is surrounded by a Faraday Cage, so I think my initial suspicion is correct. I second my initial motion for a new cable (I can do that, right? ).

Coaxial cables are in fact data cables wrapped by a hollow, flexible conductor, effectively a Faraday cage.

(from the same article linked above)

94GTLaserRC · Nov 22, 2008

mhespenh said:
I think that the woven insulators are intended to work like a Faraday cage (Faraday Cage - Wikipedia, the free encyclopedia), but must be connected- that is to say, when it was cut and "woven" back together the original pathways were broken, thus ruining its anti-interference powers. The reason it is worse when your car is on, is because of all the electromagnetic waves the various parts of your car put out when on (alternator, ignition system, spark plugs, etc). I'd try a new cable, hell, if it doesn't work you can always return it

-Michael (computer engineering student- but our sister major is electrical engineering, so its close )

*EDIT* Upon further reading, the antenna cable is essentially a coax cable which is surrounded by a Faraday Cage, so I think my initial suspicion is correct. I second my initial motion for a new cable (I can do that, right? ).
(from the same article linked above)

Well really, trying a new cable was the only option, but I put this post up while Im waiting to find who has the damn adapters for it. CC has the adapter, but it is not LONG enough to connect the radio to the end of the cord behind the glove box. I need an extension, which they carry at a local install shop but was temporarily out.

So Im guessing the surrounding wires under the insulation IS important?

Thanks
RC

94GTLaserRC · Nov 22, 2008

Just read the Article.. Nice explanatory writeup
RC

Black95GTS · Nov 22, 2008

I can't believe I just caught this one! Michael is correct. Oscillating magnetic fields will play hell with reception if the cable is not insulated correctly.

It also doesn't hurt to confirm that your grounds are fastened securely to bare metal chassis points.

Michael, my degree is in Electrical and Computer Engineering (WPI, Class of 2005), go more electrical, there is more money to be had, especially in power!

Adam

mhespenh · Nov 22, 2008

Black95GTS said:
I can't believe I just caught this one! Michael is correct.

Michael, my degree is in Electrical and Computer Engineering (WPI, Class of 2005), go more electrical, there is more money to be had, especially in power!

Adam

Truth be told, I really don't enjoy the electrical side of my major as much- I'm really a low-level hardware kinda guy (love microprocessors and assembly things). Really diggin' on embedded systems Plenty of money to be had there to live (more than) comfortably too, and hey- gotta do what you love, right?

Zero Signal · Nov 22, 2008

Yeah, if the antenna was tampered with, it needs to be replaced with a whole new piece since it's shielding has been compromised.

My brother works for National Semiconductor as an apps engineer, that sounds kind of what you'd be into. He loves his job which makes him pretty good at it.

94GTLaserRC · Nov 22, 2008

Everything you all are saying makes sense, but is it possible that the only thing wrong is the bad reception, and I would not necessarily hear engine sounds in the speakers?

Will try to find the right stuff to replace this week.
Thanks
RC

mhespenh · Nov 22, 2008

94GTLaserRC said:
Everything you all are saying makes sense, but is it possible that the only thing wrong is the bad reception, and I would not necessarily hear engine sounds in the speakers?

Will try to find the right stuff to replace this week.
Thanks
RC

Adam can correct me if I'm wrong, but I believe the nature of FM signals would lead to simply getting a crappy signal due to interference. AM is where you would pick up engine noise (I've had this problem before)- it is a distinct whine tied directly to the engine RPMS. You'll have the same problem with poorly shielded RCA cables (say for an iPod or CD changer, or in my case: Carputer)- a whine tied to RPMs. You can also get it with the dreaded "radio ghost" due to a harness under the driver's side carpet getting loose.

But like I said, electrical is not my specialty, its all magic waves floating in the ether to me

*EDIT* Did some more research, and it seems to me that because FM radio relies on changing (or modulating) the frequency (hence, FM) of a carrier wave in the VHF radio range of EM spectrum, any competing waves from your car will be "destructive" interference, totally scrambling the signal. Whereas with AM radio (where the amplitude of the wave is modulated) the varying frequency waves emitted by your car are "overlayed" on the radio spectrum your radio is "listening" in on, thus you "hear" your engine.

Okay, that sounds plausible, but I have no idea if that is based in reality at all- I'm not too good at the electrical side of physics.

94GTLaserRC · Nov 23, 2008

mhespenh said:
Adam can correct me if I'm wrong, but I believe the nature of FM signals would lead to simply getting a crappy signal due to interference. AM is where you would pick up engine noise (I've had this problem before)- it is a distinct whine tied directly to the engine RPMS. You'll have the same problem with poorly shielded RCA cables (say for an iPod or CD changer, or in my case: Carputer)- a whine tied to RPMs. You can also get it with the dreaded "radio ghost" due to a harness under the driver's side carpet getting loose.

But like I said, electrical is not my specialty, its all magic waves floating in the ether to me

*EDIT* Did some more research, and it seems to me that because FM radio relies on changing (or modulating) the frequency (hence, FM) of a carrier wave in the VHF radio range of EM spectrum, any competing waves from your car will be "destructive" interference, totally scrambling the signal. Whereas with AM radio (where the amplitude of the wave is modulated) the varying frequency waves emitted by your car are "overlayed" on the radio spectrum your radio is "listening" in on, thus you "hear" your engine.

Okay, that sounds plausible, but I have no idea if that is based in reality at all- I'm not too good at the electrical side of physics.

Well, like I said, to "ANSWER THE ORIGINAL QUESTION", just change to 'non-soldered' components, But all this is pretty darn good reading
RC

Quik03GT · Nov 23, 2008

I seem to have this same problem as well, only when the car is running. I haven't really looked into it much, my car has an aftermarket radio in it and the wiring back there looks to be an absolute nightmare. Hopefully I'll get it straightened out soon, it gets annoying

94GTLaserRC · Nov 24, 2008

Let us know if/when you look at it and the results!
RC

Black95GTS · Nov 24, 2008

I just assumed RC was rocking the AM because he is old.

Just kidding. mhespen (don't know your name) is basically correct. Its tough to diagnose it without hearing it yourself. Bottom line is that the cut antenna could cause either (or both) kind of interference when the car is running.

If you really want to get into this and enjoy the reading, look into Maxwell's equations and Laplace transforms.

Adam

madams74 · Nov 24, 2008

The shield is actually just straight to ground. You will have continuity on the shield to any ground in the car. The center wire is the only thing attached to the antenna. The little area around a solder connection is not enough to worry about. Take a meter and check from the prong outside area of the plug to ground and you should have continuity. The center pin needs to be checked and should not have any continuity between the shield/ground and the center pin. If you does, there is your problem. If it does not, check from the center pin on the radio and get someextra wire to reach out to the antenna. Find the connection on the antenna and check for complete continuity.

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