BCD436HP: BCD436HP Headphone Noise while using GPS and Car Stereo AUX port

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tlwaltz

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I have my BCD436HP set up in my car for GPS scanning during my 4 hours of commuting to work everyday. I found that the internal speaker output barely breaks over the road noise so I decided to use the AUX input on my car stereo as I have with other handheld scanners in the past. I used a 3.5mm stereo patch cord (male to male) and everything worked perfectly...until I plugged in the GPS to the scanner.

Once the GPS is added I get a large amount of what sounds like data noise/interference over the audio signal into the stereo. I tried a number of combinations with volume settings between the scanner and the but could not determine for sure whether the noise is coming from the scanner or the amplifier circuit. On headphones there is no noise, but when plugged into my AUX jack there is (but only if the GPS is plugged into the scanner). If the GPS is set up and powered but not plugged into the scanner there is no noise when using AUX so it seems to have something to do with the GPS signal once it enters the scanner. I can't explain why it isn't there while on headphones (potentially dynamic range of headphones or filtering?) but is present once sent in through the AUX jack.

I still need to perform some more experiments to isolate the problem a little better, but has anyone else experienced this?

I plan to try using an MP3 player into the AUX jack while the scanner is set up with the GPS as well just to completely rule out the possibility that the interference has something to do with the AUX amplifier circuit picking up a harmonic from the GPS as well. I am not yet 100% sure that the noise is coming from the scanner especially since I don't hear it in the headphones.
 

JamesO

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Probable a Ground Loop problem of some sort?

You could try to isolate the issue by powering the GPS unit from an external battery for a test. Something like a jump start box, some have lighter plugs built into them.

Also something like this may help??

Amazon.com: PAC Ground Loop Isolator for 3.5 MM Applications: Electronics

Might also be an issue on the impedance/load the Aux input on the car presents to the radio. Sometimes the Ground Loop Isolator may load the radio headphone circuit better than the Aux input?
 

tlwaltz

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Just to clarify I have been using the scanner running off the rechargeable batteries. I tested my iPhone on the AUX port and there is no noise even when the scanner is plugged into the GPS and running on its own speaker so the carrier is definitely riding in with the output of the BCD436HP. I also did some experimenting and found that the noise is the same regardless of the scanner volume level but does increase as I turn up the amplifier on the radio. So this indicates the noise is not part of the final audio amplifier circuit in the scanner and is likely crosstalk or a result of some sort of impedance issue. Interestingly enough if I use the scanner plugged into the USB cord powered through the car vice using the batteries the noise completely disappears for the first 5 seconds after I press the . To go into serial mode (even if the scanner passes audio during that period) then the noise returns as a constant in the background (regardless of whether the scanner is passing audio) but at drastically reduced level which seems to indicate sharing a common ground with the car radio helps.

The noise is hard to describe, it's two alternating sounds and it is the same pattern over and over again. If I get a chance I'll take a video and post it. I am curious what may be causing this.




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JamesO

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Sounds like a ground loop problem.

Even though the scanner is typically running on batteries, the GPS is NOT.

So the scanner and GPS need to be run on a battery as a test to confirm this.

If the scanner and GPS on battery are clean, then you have a ground loop problem and a ground loop isolator like the one I linked would be the easiest way to clear up the issue.
 

tlwaltz

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The plan is to test with my portable battery starter and see how that works.


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JamesO

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The plan is to test with my portable battery starter and see how that works.
Sounds like a good plan and it will yield some form of information.

The portable battery jumper may isolate and solve the issue, then you know you have a ground loop problem, might be something else you find.

Try it out and let the cards fall as they may.
 

SCPD

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bet

The plan is to test with my portable battery starter and see how that works.


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I bet it still does exactly the same noise,its a ground loop someplace,the GPS is adding noise to the system,also the scanner to the car aux is not a perfect match to begin with.It is what it is.The weird thing is try another car and do the same and it may or may not do the same.Every car is different ,every radio is different.This a factory or aftermarket radio?I bet an aftermarket.
 

tlwaltz

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Jan 21, 2004
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Culpeper, VA
I was finally able to test on my portable battery starter battery. With just the GPS plugged into the external battery power supply the noise is eliminated, so it would appear it is a ground loop issue. To k2ool's question the car stereo is the factory system. I think I have decided I am going to install an amplified external speaker anyway so I can still listen to music in the car while the scanner is in use. Now I just need to hunt down a good semi-permanent mount for the 436HP so I can see it and have it not move around too much with the external antenna, GPS, external speaker and USB charging plug connected.


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derevs

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Try getting a better patch cord, Namely one with good shielding and properly grounded. A properly shielded patch cord would be a lot thicker than the one you are perhaps now using.
If you are using an unshielded patch cord, it could be picking up R/F from the "perhaps" unshielded lead from the GPS.
 

SCPD

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Speaker

Try getting a better patch cord, Namely one with good shielding and properly grounded. A properly shielded patch cord would be a lot thicker than the one you are perhaps now using.
If you are using an unshielded patch cord, it could be picking up R/F from the "perhaps" unshielded lead from the GPS.
If its a ground loop thats not going to help him(audible tachometer,etc)

Get the external speaker and be done with it.

This mount looks beefy!
Amazon.com: Mountek nGroove Universal CD Slot Mount for Cell Phones and GPS Devices: Electronics

If you want it through the car stereo get an Fm transmitter!
Amazon.com: Monster RadioPlay 300 Universal Full Spectrum FM Transmitter MBL-FM XMTR300: Electronics


if possible (if the car radio has it) GO bluetooth into the car stereo! (this would have to be paired with yer stereo A2DP or some complex word)
Amazon.com: TaoTronics® TT-BA01 Wireless Portable Bluetooth Stereo Music Transmitter (Not A Bluetooth Receiver) for 3.5mm Audio Devices (iPod, MP3/MP4, TV, Kindle Fire, Media Players...) + 3.5mm Female to 2 RCA Male Cable: Electronics
 
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