Huge posted:Simon-in-Suffolk posted:DaveBk posted:
I have the 10kVA Airlink with multiple taps. My incoming mains is fairly high at around 246V, so I use the 250v tap and drop the output to around 230V (it's lightly loaded so the secondary runs a little high). Hum banished, noise floor lowered, no impact to PRAT.
Hi Dave, I can understand the DC offset being lowered, but I can't see how using a transformer can affect the noise floor ... unless the noise was the DC offset? Are you able to explain? HF noise (what some call 'hash') obviously couples across a transformer, perhaps you have some sort of filtering as well?
Simon, if there's an interwinding, then the HF coupling is substantially reduced. Even without an interwinding, the inductance of the transformer windings still, to some degree, selectively increases the source impedance of the HF coming through the secondary.
Huge, I was talking about HF/RF coupling rather than the specific HF induced voltages through the transformer which will decrease with frequency since we are talking HF and RF. I have been looking at this further and the idea of HF filtering gets a little vague from the manufacturers of some of the balanced transformers other than some specifically use HF filtering conditioners and use of of varistors to absorb the energy of pulses on the mains.