Tuesday, November 22, 2011

Mains filter

A friend gave me one of those new computers....a tablet...:)

...never mind the missing screen (there's an vga plug), it works and it was cheap!

My idea was to put Linux in it and use at the weekend shack, it came with windows something installed and for now will stay that way (sure not for long since I'm a bit allergic to that OS).
After some psk and rtty decoding apps installed, decided to hook it up to the FT-102. I was a rainy day and I was getting a lot of interference, I thought it was the weather but after shutting down the computer I notice the interference had gone and the only (confirmed) source was the computer power supply! Rat's! Something had to be done....

So I came up with the idea of making a mains filter idea. The other option includes a Faraday cage for the power supply or getting another computer.

Here's the assembly of the interference filter for the mains power supply:

well....did it worked?.....no and not tested yet, after powering it up (I should had tested before closing the box) the VDR blew up, I guess that it was underrated or I didn't looked very well to the schematic of the donation computer power supply were I removed it and probably the VDR was not on the mains line and was not rated for over 230V.

Now that I removed the broken VDR I have to wait for the next weekend to conduct further tests.

Here's the schematic used:

..never mind the VDR (it's just for spike protection), it's not installed at the moment. If you duplicate this, get capacitors rated for at least 500Vrms, the ones I used are rated 1KV and came from a computer power supply.
The number of turns it's not critical as long as they don't create a lot of impedance on the mains 50Hz....I guess something bellow 1000 turns it's ok :) The idea is to create some high impedance on HF and VHF.

I also placed a ferrite core (the ones used in computer power cables) around the cables as a "won't hurt, probably will help" option.

The white output is the filtered one (it's an old household mains plug), the other two are input and a not filtered output, they came with the donated box (a broken computer power supply).

There's no reason for this schematic do not work at least reducing the level of interference. If it reduces all ,then it's a bonus.


PE4BAS, Bas said...

Hello Ricardo, that is a 'big' filter. I prefer the small commercial ones myself. But from a homemade point of view this could be working fine if you have room for it. 73, Bas

Ricardo - CT2GQV said...

Hello Bas,
Indeed it's a big filter. I have a smaller commercial one but it's more fun to blow some VDR's :). I also have one of those filter panel input plugs but couldn't find it....
73 de Ricardo, CT2GQV

LY2SS said...

I don't get it. Does it work eventually ? :-)

Ricardo - CT2GQV said...

Hello LY2SS
It works if you consider that having 230v at the output is working :)
Regarding the interference removal I only can test during the weekend. I will post as soon as I tested it.

LY2SS said...

ok. It'll be very interesting!

Best 73!