"Dave Platt" wrote in message
...
I would like to use my computer for logging as I work DX stations, would
like to try PSK31, etc. BUT.... the computer wipes out half the HF bands.
I
waited until the hard drive went into sleep mode and the RFI was much
better. I tried grounding the computer case to an earth ground but to no
avail. Anyone else have this problem and how did you remedy it. My box is
not super fast, being a mere Intel PIII 450 mhz proc. It has the usual
things, vid card, external modem, and sound card. Your help appreciated.

Does the RFI appear only when the disk is being accessed, or is it
present at all times when the disk is spinning?

If the former, you might be able to snub out some of the interference
by installing ferrites on the data cables from the drive to the
motherboard. You can get clamp-on flat ferrites for ribbon cables, or
clamp-on split-ring ferrites for the newer-style round "high airflow"
cables. Install ferrites as close as possible to the drive, and also
at the motherboard end of the cable.

If the interference is present whenever the drive is spinning (and not
just when't being accessed) then the RFI may be coming from the
drive's onboard CPU and DSP. Damping down this RFI within the cabinet
is likely to be tricky to do, as adding a shielding/damping material
(e.g. a ferrite sheet) to the drive controller PC board might cause
drive overheating, or might short out something on the board.

You could try clamping ferrites on _all_ cables leaving the case...
monitor, keyboard, mouse, etc. It's possible that EMI from the drive
is being conducted out on these cables.

You may need a better-shielded case. I've seen a lot of cases on the
market which don't appear to have good shielding properties... the
sides are plastic (often without an anti-conductive coating of any
sort), there are no (or ineffective) contact flanges to tie the sides
to the case, etc. My hunch is that a lot of PCs built with this sort
of casework (by e.g. smaller, neighborhood or regional PC-builder
shops rather than national manufacturers) probably don't meet FCC
Class B EMI radiation/conduction limits.

The cases I've seen sold under the Antec brand name seem to be pretty
good ones - solid metal sides, metal shielding for any unused
chassis-front drive bay, good contact flanges between surfaces, etc.
=============================
Perhaps you should also suspect the switch mode power supply unit of your
PC.
even if it is fully metal enclosed . The 230 or 115 V AC filter might also
be sub-standard .
The latter could allow RF type sigs to pollute the power supply system and
hence your radio.
This can be checked partly by temporarily running your radio off-grid
,through a 12V battery ,if that is possible.

Frank GM0CSZ / KN6WH