On Sun, 27 Nov 2005 13:19:18 -0500, Jim Jarvis wrote:
>I'm dubbing all CD's into iTunes in a mac-mini,
>and feeding the stereo via a line input (vcr-2) from a 16 ohm phone/
>speaker line out of the mac-mini.
Virtually ALL computer audio interfaces have massive pin 1 problems, and
are thus open doors for common mode RF. In other words, those audio
interface cables function as antennas, and the resulting RF current gets
inside the box via the pin 1 problem.
The easiest fix (without modifying or switching to different equipment)
is usually to add suitable ferrite chokes to the interface cables
For a lot more detail on pin 1 problems, RFI to audio gear, and how to
use ferrite chokes, see the publications section of my website. There's
a lot of excellent data measured by another ham.
By the way -- the #31 Fair-Rite 2.4" O.D. toroids, by far the most
useful part for HF suppression, are now available from Fair-Rite. It's
Fair-Rite P/N 2631803802. Ham resellers would call it FT240-31 and sell
it for around $10. It's a LOT cheaper from Fair-Rite's distribution
using the Fair-Rite part number. Several clubs got together and did a
group purchase of 2,000 pieces. We got them for under $2.00 direct from
Fair-Rite, including shipping. They're under $4.00 at less than 250
Computer gear also tends to be totally unshielded, but the interior
wiring is usually too short (as a fraction of a wavelength) to be very
susceptible at HF. VHF and UHF is a different story -- both unshielded
boxes and pin 1 problems are major mechanisms, and when you fix one, the
other may still be significant.
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