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[OT] RF Interference
Hi all,
I'm looking for a way to stop RF interfence in a taxi, from the 2way/computer, etc on weak radio stations. The whole setup includes a 2way, taxi meter, computer (used for dispatch), and security camera all integrated together. Whenever the equipment is turned on, weak stations (such as ones from interstate) are subject to whining type noises that are sometimes constant, and other times vary with acceleration/deceleration. I might add it's an on-glass antenna with booster (oem installed) for the radio, I know that makes for weaker reception. Any help on where to start would be great.. Merry Xmas All, Chris |
#2
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Speaking as software engineer who knows some electronics (ie not a car
electrics expert)... Interference can be radiated as rf energy from other equipment, or present on the power leads. If it is radiated rf energy then this can be fixed by reducing the rf energy radiated by the interfering devices - the action required may be device dependant. A better placed antenna would probably help against this kind of interference -ie not close to interference sources - above the roof would be aa good place shielded from the interfering equipment by the metal roof. If it is present on the power leads then this can be reduced by filtering the power leads (blocking high frequencies) -an inductors in series with each power line, and a capacitor across the power lines will help this. These could be placed close to the radio power input, and it may also help if they were placed close to the power inputs to interfering equipment. I imagine there must be standard components available for car environments for this job from somewhere like Halfords (a UK car parts shop). Do you mean that the whining varies pitch as the engine speed varies? If so then my guess is that this component of the interference could be due to inadequate filtering on the alternator or the ignition system - possibly a capacitor has broken down and needs replacing. If the interference is only there when the extra equipment is turned on then that suggests that it is more likely alternator than ignition (as the ignition effect would stay constant, the alternator current would have increased). Hope this helps "Skeleton Man" wrote in message ... Hi all, I'm looking for a way to stop RF interfence in a taxi, from the 2way/computer, etc on weak radio stations. The whole setup includes a 2way, taxi meter, computer (used for dispatch), and security camera all integrated together. Whenever the equipment is turned on, weak stations (such as ones from interstate) are subject to whining type noises that are sometimes constant, and other times vary with acceleration/deceleration. I might add it's an on-glass antenna with booster (oem installed) for the radio, I know that makes for weaker reception. Any help on where to start would be great.. Merry Xmas All, Chris |
#3
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Interference can be radiated as rf energy from other equipment, or present
on the power leads. If it is radiated rf energy then this can be fixed by reducing the rf energy radiated by the interfering devices - the action required may be device dependant. A better placed antenna would probably help against this kind of interference -ie not close to interference sources - above the roof would be aa good place shielded from the interfering equipment by the metal roof. Firstly thanks for the reply.. much appreciated.. The on-glass antenna is simply a flat coil on the rear windscreen (looks much like the window demister, except a loop not flat). An external antenna isn't really an option as the car is brand new and I would prefer not to drill holes, etc. (as would the owner) Is there some kind of filter or shielding or something I can place near the equipment, etc ? If it is present on the power leads then this can be reduced by filtering the power leads (blocking high frequencies) -an inductors in series with each power line, and a capacitor across the power lines will help this. You mean like a Pi filter ? How do I determine the required values of caps and coils ? (I was thinking 2 coils in series with +12V, and 2 caps between power and ground) Would I be best using variable capacitors and adjusting untill I get the best result, or just a fixed value that covers a wide frequency range ? Do you mean that the whining varies pitch as the engine speed varies? If so then my guess is that this component of the interference could be due to inadequate filtering on the alternator or the ignition system - possibly a capacitor has broken down and needs replacing. I double checked and the interference from the equipment doesn't vary, the one where the pitch varies with engine speed occurs when the equipment is off.. (probably occurs when it's on too, but the first problem drowns it out). I would very much doubt a broken down cap as the car is brand new (forgot to mention in my original post). Will a Pi filter on the power leads to the radio help with this interference too ? Regards, Chris |
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