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Old 08-24-2005, 01:03 PM
dougie_monty dougie_monty is offline
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Radio static on cassette players

I have a portable cassette player I play in a car (I can't afford to have a cassette player installed in it).
I'll be playing cassettes--I live near the Harbor Gateway district of Los Angeles--and hear an annoying dat-dat-da-dat-da-dat come out of the speakers (something like a "dotted rhythm" phrase in music).
What kind of radio signal can override the tape mode of a cassette player/radio? I never use that radio on the unit, just the car's own radio, which doesn't do that.
(In the early 80s I once got CBS radio on a portable cassette player which did not come with a radio.)
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Old 08-24-2005, 01:09 PM
CookingWithGas CookingWithGas is offline
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WAG here but it could be some EMF interference not necessarily in the radio band. Not sure what could cause noise on a tape head but they are magnetic devices.

I used ot have a Nextel phone that caused speakers to make a noise like that just before it started ringing.
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Old 08-24-2005, 01:24 PM
MsRobyn MsRobyn is offline
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If you have a cell phone near the speakers, it will make that sound. It's your phone pinging the tower for time and date and all that fun stuff, and the signal tends to be audible through a speaker.

Robin
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Old 08-24-2005, 02:20 PM
engineer_comp_geek engineer_comp_geek is online now
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If it was a little more regular I'd say it's spark plug noise, but spark plugs usually don't make a dat-da type pattern. It could be RF noise from traffic detectors that are placed on a lot of roads to monitor the speed of traffic, so that they can tell when there is a problem. If "Harbor Gateway" is a ship type harbor it might be ship radar.

A tape head puts off a VERY small signal, so there's a really high gain amplifier that takes the signal from the tape head and makes it into something useful. If that amplifier (and the power supply that feeds it) isn't extremelely well shielded then RF noise will very easily get coupled into the audio path. It's actually a very common thing with portable cassette players. It makes your life miserable if you try and listen to cassettes and you happen to be near a radio transmitter. When I was in college you couldn't play a cassette player in the engineering labs on the top floor, because the university radio station (whose antenna was mounted on the roof) would come through louder than the music from the cassette.

If you have the cassette player plugged into the cigarette lighter for power then adding ferrites to the power cord might help. Ferrites are little clamp on thingies that cut down on RF noise. They used to sell them at Radio Shack. Not sure if they still do. This will help to prevent your power cord from working like a radio receiver antenna, which might be one way the noise is getting into your cassettes. The circuit boards inside the cassette player might be acting as antennas too, so I won't guarantee the ferrites will do anything.
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Old 08-26-2005, 04:08 AM
dougie_monty dougie_monty is offline
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Quote:
Originally Posted by engineer_comp_geek
If it was a little more regular I'd say it's spark plug noise, but spark plugs usually don't make a dat-da type pattern. It could be RF noise from traffic detectors that are placed on a lot of roads to monitor the speed of traffic, so that they can tell when there is a problem. If "Harbor Gateway" is a ship type harbor it might be ship radar.

A tape head puts off a VERY small signal, so there's a really high gain amplifier that takes the signal from the tape head and makes it into something useful. If that amplifier (and the power supply that feeds it) isn't extremelely well shielded then RF noise will very easily get coupled into the audio path. It's actually a very common thing with portable cassette players. It makes your life miserable if you try and listen to cassettes and you happen to be near a radio transmitter. When I was in college you couldn't play a cassette player in the engineering labs on the top floor, because the university radio station (whose antenna was mounted on the roof) would come through louder than the music from the cassette.

If you have the cassette player plugged into the cigarette lighter for power then adding ferrites to the power cord might help. Ferrites are little clamp on thingies that cut down on RF noise. They used to sell them at Radio Shack. Not sure if they still do. This will help to prevent your power cord from working like a radio receiver antenna, which might be one way the noise is getting into your cassettes. The circuit boards inside the cassette player might be acting as antennas too, so I won't guarantee the ferrites will do anything.
Thanks...
"Harbor Gateway" is not close to the Harbor--it's several miles away. It's along the "L. A. Strip," which is a level land route between Wilmington and downtown Los Angeles.
I guess I can also try to run the cassette player off batteries and see if that stops the static...
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Old 10-16-2005, 01:54 AM
dougie_monty dougie_monty is offline
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Quote:
Originally Posted by MsRobyn
If you have a cell phone near the speakers, it will make that sound. It's your phone pinging the tower for time and date and all that fun stuff, and the signal tends to be audible through a speaker.
Robin
I think that's it: I carry the cell phone in the car, of course, and the closer it is to the speakers on the portable cassette player (which I keep on the front seat so I can reach the controls as I drive) the louder the static. Perhaps I'll try the ferrites, or putting the cassette player in an open metal box, or both. (I had already disconnected the player's exterior radio antenna, and still got the static.)
The sound also was heard on my Walkman, when I was riding a Greyhound Bus to Las Vegas and had the cell phone nearby.
Thanx
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