[Ham-Computers] RE: hash w/o the corned beef

[Hsu, Aaron (NBC Universal)]

The chief culprits are the switching power supplies, especially cheap "mom and pop" store specials.  Many of them lack any RFI filtering on the AC inputs.  If you open up the supply, you'll often find locations on the circuit board where caps and chokes could be mounted, but they're left out to reduce cost.  

There are pre-made RFI filters that fit into the AC socket (IEC type) on the power supply.  Basically, the cheap "connector only" socket is removed and the RFI socket installed in it's place.  Mouser, DigiKey, and others sell these for about $5 - $10.  Do a product search for "IEC RFI Filter" and it should bring up some hits.

Another source is the video card and cable.  Make sure the cable has pre-molded ferrite chokes ON BOTH ENDS.  Other connectors and cables can also be a source, but are less of a concern.

Have you tried to turn off the monitor or even your TV-set?  Actually, not just turning it off, but pulling the plug.  The power circuitry in many TV sets are switching type and cause quite a bit of hash.  Turning off the set doesn't help as the power supply still draws power to monitor the "soft-power" switch (same for modern computers).  Also, don't discount those "wall wart" type power supplies as many of them are now switchers rather than linear.  The power brick for one of my Toshiba laptops puts out low-level hash every 50KHz or so across 40M and 20M...quite annoying.

73 and GL,

  - Aaron Hsu, NN6O


p.s.  BTW, what's wrong with tuning the radio from the other room?  Isn't that a feature that everyone's clammoring for?  Look at all the hub-bub about new "Software Defined Radios" (SDR's)....

Yuck!  For me, give me a knob and more buttons - can't stand stepping through 10,000 menus to adjust the mic gain!


-----Original Message-----
Sent: Monday, January 22, 2007 1:12 PM
Subject: [Ham-Computers] hash w/o the corned beef

My computers are wreaking havoc upon my radios.

I just tried putting some ferrite donuts around the power cords, resulting in a zero db reduction.  I might as well have eaten them.  I have an indoor loop and outdoor antenna; switching makes no difference.

I'm going to try reorienting them, but what other practical solutions are there?  I'm not limited to one room, but since I spend a lot of time there, I'd prefer to have radios and computers both in the room.

Face it - it would be pretty silly to try tuning a radio in the next room.


Thanks,
jeff