Speaker Interference?

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ZBeeble
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Speaker Interference?

Post by ZBeeble » Sun Jul 24, 2005 6:06 pm

I've been using my treo a lot more, recently. It's a GSM treo and I've always noticed that GSM phones interfere with speakers that are "powered" ... not even necessarily with the volume turned up --- just "on".

This is just an annoyance until I've been using my Treo as an MP3 player in my truck. Every time we switch towers (about every 10 to 20 minutes in the country) I get to listen to the GSM chatter in addition to my music.

Any way to build the cable to eliminate this?

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spymongoose
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Post by spymongoose » Tue Jul 26, 2005 1:42 am

Here's a thought, get yourself a CDMA phone. CDMA networks are more common than GSM so you may find that you get better reception all around, especially in the country. As for isolating and removing the interference there isnt any reason in the first place that your phone should be doing that. It is possible to induct a voltage into a wire from a transmitting device, but what you're describing shouldnt be possible. Cell phones shouldnt transmit enough to induct your audio cable with "chatter." One way to see if your phone is actually causing this chatter is to turn the wireless mode off, (i.e. turn off the cell phone part) and to be fair make sure the bluetooth is off as well, and drive around playing your mp3's. Its entirely possible that either your mp3's are corrupted or there is some sort of cpu loading delay causing your chatter, whitch you could prove by removing any possible inductance causing devices from the system. Good luck and let us know what you find.
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ZBeeble
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Post by ZBeeble » Tue Jul 26, 2005 1:37 pm

Well... it may be your experience that CDMA is more prevalent, but here in Canada, and more specifically, the GTA, GSM is a better choice. The GSM providers are also better. My company is also considering becoming a virtual GSM carrier. CDMA, for me, is highly unlikely.

Anyways, to your second point, maybe 'induct' is the wrong term. I was kinda hoping some EE experts might be around. This interferance is a well known phenominon --- at least ... every GSM phone I've had has done it. It's worth repeating that this requires that the speakers be "on" ... so it's likely some aspect of the amplification that involved here.

BusDriver
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EMRFI

Post by BusDriver » Mon Aug 01, 2005 7:56 am

Electro-Magnetic Radio Frequency Interference...ANY radio frequency transmitter can cause the interference you've described through the speakers in your car. When I hear the the interfenence start in my car, I know my phone is either:

A-Changing cell towers
B-About to ring with an incoming call
C-About to alert to a recieved SMS or e-mail

If you lay your Treo 650 next to a computer monitor, you will (harmlessly) see the same interference. (Now let's not be pressing the phone to the monitor or any other idiotic thing like that.)

ZBeeble
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Post by ZBeeble » Mon Aug 01, 2005 9:21 am

Well... Those are all things I know. The old TDMA phones used to do this really badly. I think that GSM seems worse in this regard because the tranceiver turns itself on and off at a fairly high frequency (200 or 300 times per second?)

Anyways... I was rather hoping that some EE type here would pop up and say that some amazingly simple choke design ... on the headphone lead wire, for instance, would eliminate the problem.

I have noticed that the intensity of the problem can be varied with relative positions of the device ... and I think that the major cause of the problem is the headphone lead wire (which in my case is then going to an FM transmitter) ... but I assume the problem would be the same for people who hook up through a fake cassette cartridge and those who have a direct line-in to their headunit.

BusDriver
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Solution Unlikely

Post by BusDriver » Tue Aug 02, 2005 9:23 am

Possibly wrong here. Even if you got completely away from a cable connection, say with a bluetooth car kit, the EMRFI will still be there. The interference your experiencing doesn't need wires to travel.

ZBeeble
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Post by ZBeeble » Tue Aug 02, 2005 1:02 pm

True enough in theory... However, when my phone is in the truck and I'm playing the radio or CD (not using the FM transmitter), the interference is not noticable.

robber
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Post by robber » Mon Oct 10, 2005 12:41 pm

Can you please explain the setup in your truck with a little more detail?

thx

ZBeeble
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Post by ZBeeble » Tue Oct 25, 2005 2:06 pm

robber wrote:Can you please explain the setup in your truck with a little more detail?
It's pretty simple:

Treo(2.5 jack) -> 2.5 to 3.5 converter -> FM transmitter

This is then received by the Truck's radio. I can't do a line-in because Ford's radio doesn't allow a line-in (at least, not the one I have). Nobody is selling a line-in for this radio in the aftermarket, at least.

What I'm wondering is: Is there some sort of Choke or circuit or something that I can add to this setup that will eliminate the RF interference or induction or whatever?

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