[ProAudio] AES on the west coast, was Re: Ampex/ProAudio List Dinner

proaudio at bach.pgm.com proaudio at bach.pgm.com
Wed Nov 6 13:05:36 EST 2019

In general it is the low frequency RF emissions which escape in the differential mode becoming more common mode as the emission frequency increases.  This I primarily due to the return path for the interference currents tending to be via stray capacitance to the chassis ground limiting the common mode current at the lower frequencies.  Whilst you are correct that reciprocity applies to the coupling of the external field to the circuit via the cable the overall susceptibility will depend more on the wanted signal type.  Digital signals are generally more robust to continuous disturbances such as an RF transmission but less so to transients or particularly bursts of them.  Analogue signals however are more readily disturbed by continuous, especially amplitude modulated, transmissions.  Transients are often a minor disturbance due to their short duration.  

IF you want to keep RF out of your signals the best option is a good screened cable with 360 degree screen terminations at each end to a well designed shielded enclosure.  Balanced twisted pair within will deal with the VLF magnetically induce interference.


> On 6 Nov 2019, at 20:31, proaudio--- via ProAudio <proaudio at bach.pgm.com> wrote:
> On 11/6/2019 12:22 PM, proaudio--- via ProAudio wrote:
>> 10BaseT is a brilliant standard!  I've told folks for years that Ethernet is the only digital interface (aside from optical) to even consider when the electrical environment is hostile.
> As implemented in consumer equipment, wired Ethernet with UTP is a notorious source of RF noise from HF through low VHF. HF noise is radiated common mode; I suspect that it's differential mode at VHF. Thanks to reciprocity, such a system will also be subject to interference from strong RF fields.
> Jim Brown
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