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Author Topic: New shack..choke & bypass caps on mains circuit?  (Read 5504 times)

Posts: 19

« on: August 07, 2012, 01:08:21 PM »

Rebuilding my shack, I'm putting everything on one separate 20amp electrical circuit that I've just added. (2KW+ is more than adequate capacity for the equipment I run.)  I had an idea I wanted to get some feedback on from any knowledgeable folks. 

What about putting some RFI filtering on that circuit "before" any power plugs? I would set up a junction box containing a toroid onto which both 12 AWG  power wires (white and black) are wound several turns.  I'd also add a bypass cap (say .01mf, 6Kv) to ground from each side of the mains (i.e. white to green and black to green). Then run the power out of that box to the regular box-mounted AC power plugs.  The aim would be to filter out incoming RFI and clean the power a bit - but also outgoing RFI I guess (I'm not intending to generate any of that Smiley.

I frequently see this kind of choke + bypass caps filtration within power supplies, switchers in particular, (usually with ferrite beads rather than wound toroids).

Anybody done this to a mains circuit? Thoughts pro or con?

- Les, W9XC

Posts: 6251

« Reply #1 on: August 08, 2012, 04:01:23 AM »

If there is such noise on the circuit or in the building, it's better to see if you can find the source of the noise rather than try stopping it at the shack entry point.  Noise like that usually means a bad/loose/failing connection or an appliance or device that is ready to fail.

Other than that, I would opt for a commercially made plug in filter/conditioner and run any power lines to my equipment through that.  Keep in mind that insurance companies and adjusters may well look at anything homebrewed and built in like you propose with a dim view--unless that equipment has a UL rating.  

I myself use a Nady Audio PCL-800 power conditioner and a Lite Quest 8 switch/outlet switch box (both rack mounted types, kept when I got rid of my DJ equipment) to run my shack equipment through.  I got them used and paid about $20 each for them. The conditioner has an 1800 watt rating, which is plenty for my equipment, and a master switch that will shut off anything plugged into the conditioner.

The 8 position switch box is simply for convenience for equipment that is out of my reach when I'm seated.  Right now I'm only using four of those switches.  I simply built a small niche into my desk shelving to hold them.  There's no need for an entire rack--unless you want to use one, that is.

Good luck amd 73!
« Last Edit: August 08, 2012, 04:05:11 AM by K1CJS » Logged

Posts: 9748


« Reply #2 on: August 09, 2012, 10:39:49 PM »

I wouldn't know why anyone would want to do that.

It might have been important when power line leads ran through chassis next to input coils on receivers.

Nearly all radios today have well over 100 dB of power source to receiver isolation at HF.

I can't imagine very many cases where a noise source could work into the system via conducted noise into the gear at levels even approaching what an antenna would pick up from radiation between the noise source, power lines, and the antenna. I've certainly never seen a case of that.

I wouldn't bother. What you do with antenna feedlines and balance is far more important.

73 Tom

Posts: 6251

« Reply #3 on: August 10, 2012, 05:13:52 AM »

There are still people who like to run boat anchors and or who homebrew some of their own equipment, Tom.  From the sound of it, maybe this gentleman is one of those who do.

Posts: 7718

« Reply #4 on: August 10, 2012, 05:14:38 AM »

I would be careful. To comply with UL design requirements you need to use double insulation and "safety rated" capacitors.

Posts: 19

« Reply #5 on: August 10, 2012, 07:23:37 AM »

First, thanks to all who replied with very useful information.

Chris (K1CJS), yep, I am one of those homebrew and boatanchor types. That was partially why I was asking. But you also jogged my memory that I have an 1800W ART PB4x4 Power Distribution Unit packed away that I used to use for audio (with surge, EMI/RFI). So why do the work myself if I want any of that?

Tom (W8JI),  "Nearly all radios today have well over 100 dB of power source to receiver isolation at HF."  As usual, you cut to the chase with definitive information (which I didn't know), and I thank you for it.

Dave (WX7G), thanks for the safety/UL points, very good ones.

Conclusion: I'm going to forget any of my own superfluous in-line power conditioning mods and go as simple as possible.

Thanks again, all,

- Les, W9XC

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