| Electronics > Beginners |
| Phone noise on an audio set, how to explain this to layman |
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| Kjelt:
Thanks all, quite usefull answers. So what is the "opening" this gets in the audiosystem, I suspect the interlinks which if not balaced are poorly shielded ? Or are the holes in the chassis for convection already large enough? |
| Brumby:
While openings in a case might provide some avenue for RF penetration, my observation is that wires running to the amplifier are a prime source. They act as antennae, picking up any EM radiation around. Inputs are normally shielded, but given a strong RF signal, even those shields may not be sufficient. Power leads can also pick up RF which can make its way into the circuitry - and then there are the speaker leads. These are usually unshielded, making them a good antenna. They can pass RF into the amplifier circuitry and may be enough for it to find its way to a susceptible part of the circuitry. |
| Kjelt:
Yes I also have doubts about speakerwire, I thought since they are driven by low impedance outputs they would be unsusceptible, if not it makes me wonder about companies selling these kinds of "litze style" speakercables, excellent antennas. https://goo.gl/images/HrUSXy |
| Richard Crowley:
Audio gear is generally susceptible to RFI penetration especially through input connections, and especially low-level (high-gain) microphone inputs. It is possible to add RF filtering to most input (and output) ports, but most audio gear doesn't implement RFI filtering since it has been a relatively rare problem, at least before the cell-phone era. One of the most popular brands of audio connectors (Neutrik) even makes a range of connectors with RF filtering built-in. NC3MXX-EMC |
| Marco:
--- Quote from: Kjelt on October 04, 2018, 08:22:02 pm ---How can I tell in layman's terms why an 800MHz or higher portable phone with its 1W power can cause interference on an audio set (20-22kHz), you know the noise just before the phone rings. --- End quote --- If you want to put in effort then show don't tell. Try to construct a discrete audio circuit with high input impedance and input protection prone to mixing (low capacitance RF Schottkys?) and make a phone call. Then you can point to the diodes and try to explain mixing and say rectifying junctions are present in all amplifiers. |
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