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Author Topic: Flex-Radio Computer power supply RFI  (Read 11447 times)

Posts: 19

« on: December 04, 2013, 11:54:12 PM »

The computer I'm using to run PowerSDR for my Flex3000 I found to be the source of some really bad RFI. After doing some research online on the subject I've determined that it is the power supply as it's quite a wide bandwidth. Also I disconnected everything else from my computer and it was still there.

When the computer is off, the RFI drops right off.

There's a little RFI from the monitors but I can deal with that separately.

It looks like my options are the following, getting some FT-240-43 ferrite cores to wrap the power cable around. Use an AC-line filter. Or finally, I'm contemplating getting an MFJ-1026 interference canceller.

There seems to be all kinds of ferrite cores out there and they seem to go by different names. But I can't seem to find these exact types. I live in Calgary here in Canada but I'm heading to Phoenix this weekend and plan to pop into Ham Radio Outlet ( and see what they have. They have a few ferrites but the only one that seems to make sense is the MFJ-420-7510 which states it's an AC filter. However it says it's only good down to 20 Mhz.
The RFI I'm experiencing is extremely bad on 80m. right at 3.578Mhz. This is right in the JT65 zone which I've been playing in recently.

The next option is the AC Filter. Again at Ham Radio Outlet is the MFJ-1164B. Any opinions on how effective this may be for my situation?

Third I have the MFJ-1026. I think I will get this regardless just due to the fact that I have multiple RFI interference in my shack due to all the computer equipment around. Particularly I can see the ethernet noise. But at the very least it sounds like it would be effective for my computer's power supply noise.

Also I should mention my ground situation as I'm sure it's less than optimal. I have my antenna up on my roof, two stories up from the ground. I have a ground plate hammered into the ground directly below it and have a ground wire going from the mast down to the the plate. I then have my antenna leads coming down, into the house, down to the basement and clear across to the other side of the house. Not a perfect scenario I know but antenna position and location of where I could have my shack dictated this situation.

In my shack I have a cold water pipe above me in the ceiling where I've clamped a large ground wire to. This in turn comes down the wall and over to my radio rack a distance of about 12 feet to a common screw down point. I then have ground wires coming from my radio and power supply to this point.

My concern with my ground is that it's not common to the same grounding location as my antenna. Also my computer itself is only grounded via the AC cable to the wall. Finally the cold water pipe has to run all along the house to the other side of the house again before it hits the main water line that comes in from the ground. This seems like a very long ground and I therefore either have ground loops or I'm not even truly grounded at all. I had a read an article speaking to this earlier today. He talked about a solution of running coax from the shack to the ground rod location and soldering the copper core and shielding together at the ground rod location and using a capacitor at the other end in the shack to connect the shielding and core. Perhaps I may need to look into this?

Anyway, sorry for the long run on ramble here. I appreciate any suggestions, opinions, or solutions you may be able to provide.

Thank you!



Posts: 184

« Reply #1 on: December 05, 2013, 02:05:52 PM »

Replace the power supply.  This could be a cheap power supply with no EMC/RFI filtering.


Posts: 19

« Reply #2 on: December 07, 2013, 01:28:49 AM »

Thanks Richard. this is exactly what I ended up doing and I managed to clear up a huge amount of the RFI.

However now I've discovered that the ATI Radeon video card I have inside the computer is causing it's fair share of RFI. Not nearly as much as the power supply was but enough to make communication on the 80m JT65 frequency troublesome. Do you think an AC-Line filter would help here or is this RFI leaking straight out of the box and I need to find a different video card? I installed this card so I could get 3 monitors going off of this PC. Useful for all the windows I end up having up for my digital comms.

I'm currently in Phoenix so plan to stop by Ham Radio Outlet on Saturday to see what they have (we don't really have a great amateur radio store in Calgary, at least not a well stocked one.)

Thanks again for any suggestions.


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