|
Posted by Glenn on May 02, 2026 at 02:55:46.
|
I told you not long ago that I ordered an AC Line Filter with the hopes of removing some of the low frequency noise from my 120 Volt house power that makes it into my antenna. I looked high and low for something that might work. I ordered several samples from US suppliers which didn't even come close. They are very good at isolating noise of higher frequency. I found one that had specifications in terms of frequency range. It was made in China. I decided to order it because they at least wrote their specifications out while most others don't. It also looked very well built but I couldn't tell much about it without seeing it close up. When I received it I took it into my lab and hooked up a VNA to the filter. It did very well removing common mode noise but did very little for differential or normal noise. In fact the best it could do to remove some noise was starting about 90 Khz. Most of my noise is strong starting around 60 Khz and the harmonics continues on up. I looked closely how this filter was wired and discovered that they had two sets of common mode filters in their circuitry. No differential mode inductors. I have studied line filters the last few weeks and I knew that their method does not make sense. I am guessing but I believe they just copied a standard circuit to some degree but didn't have the knowledge to spot their mistake. AC line filters usually have both differential and common mode inductors in them. This is because many of the new power supplies (switching mode) contain both and can propagate this noise back into the power system. Lately the FCC has done a lot to stop this but many older devices have no protection. Very few from China do and I don't think they care that much because they are allowed to sell their equipment basically unchecked. Our homes are full of noise makers which create noise from 60 to 400 Khz and it will travel down the power line. I am in the process of modifying the filters I bought to filter differential noise out of my power. I used a portable SDR with a loop antenna to study where my low frequency noise was originating from. It's mostly coming from phone chargers, LED lights, computer screens and computers. Small amounts come from my microwave and television. This noise I have is not that bad but it does ruin any attempt to do any listening around 60 Khz and about three octaves higher. The big noise that has bothered me (if you remember I called it the Binaca Blast) comes when the power company shuts down their SCADA polling on their power line. But they stopped shutting down their polling. They poll all the time. And I have not had the Binaca Blast since they left their system on all the time. Well, I am still working on the noise issues but I have so many things that I need to get done. I will get around to it and will let you know how it came out.
|
Follow Ups:
|