The AM Forum

Upon further investigation I discovered the neighbor's desktop computer generation enormous RFI.  I asked if anything was changed with it and they informed me that they had the power supply replaced a month ago as it wouldn't power up. Any ideas to get rid of the noise.  I tried ferrite beads on the power cable to no avail.

I had a desktop do that with its ethernet adapter.  It was connected to a long (abt 30') CAT 5 cable, which made a great antenna.  Fixed the problem with a 6' cable, connected to a hub.  The long cable went on the hub, no further problems.
See what happens when you pull the network cable off the PC.  Just one possibility.

Steve WA1QIX was talking on the air just a couple days ago, and said he added a "couple caps" and amybe an inductor to the supply, on the AC line....

said it's an easy fix for the really cheap supplies that have NO filtering.

Older junk compuker supplies are a good source of filter parts. Often they will fit right in where the line filter has been left out. Look for chokes and caps right near the female line socket.

Clearly the power supply is the problem. It's probably a switcher. Find an analog equivalent and your problem is solved.

Jay,

   If it truly is the desktop computer power supply, it will be a switcher. I doubt if an analog version will be available. I'd look at the make and model number, and see what you can find out. Some of the really cheap stuff isn't UL listed. The better supplies out there are power factor corrected (PFC), and are modular such that you plug in the wires needed. The cheaper supplies have a wad of wires and no PFC.

   A UL listed, PFC supply with modular design is the best bet, but it is still a switcher.

   This situation puts you into a bad situation. If you do anything to the computer you will likely own every problem that occurs. If you do nothing you receive hash. The options are not good.

Regards,
Jim
WD5JKO



   

PROBLEM SOLVED.....SO FAR
the neighbor was kind enough to let me open the tower
i found a 300 watt universal switcher in place of the original
i tried to snuff out the noise with toroids to no avail
i then decided to replace the supply with a mid grade version from best buy
i figured it was a cheap investment and a backup for my own tower
installed in just 10 minutes and tested for noise with a portable radio
no noise present at the moment
i asked them to leave it on a while to see what happens

Here's one to add to the RFI noise list as well:

Recently I had a "SCHEETZ-SCHEETZ-ZZZTTT" 40 over 9 type of periodic noise suddenly appear around 3885. Turns out it was simply strongest there but also had some RFI on 7.150 as well but down about 3dB there.

I turned off all circuit breakers one at a time for a minute each, no luck.

I took my G3 recever outside and around the house to the power transformer box, nothing. The farther away from the house, the lower the noise.  ???

I came back into the house and the noise was stronger. Okay, extend the antenna and put the receiver near the smoke detectors. Nothing. Placed it near the Modem and cable coaxes, not much there. I placed the receiver near the LED light bulbs and the CFL's around the house and - notta.

I happened to turn around in the family room and the noise increases as I go toward the grandkids portable DVD player which was charging on the stair well. Bingo! :D

I unplugged the wallwart and the noise started to reduce in intensity. Apparently, even after unplugging, this critter was still creating noise. After about 7 minutes, the noise at the DVD walwart finally died out. To top it off, the DVD charger has a ferrite slug on it just before it enters the back of the DVD, but injects RFI through the 120V plug. ::)

I suspect the charger has a capacitor that powers a "keep-alive" circuit going for a few minutes until complete discharge.

Phil - Ac0OB