Fred, W4JLE raised a number of intresting points. DC to DC converters
are switching types to get high efficiency and this can generate many
harmonics. If not suppressed, as many converters are, this causes much
noise. The solution is to use the proper converter if required.

Yes England can be well received all over the European continent. The
transmissions are powerful and decline only about 6 dB every time
distance from the transmitter is doubled after the first 1.5 km from the
200 KHz transmitter.

The questioner referred to his truck cab as a "steel box". I accept his
word. However, I once had a Corvette with a fiberglass body. The
ignition system came well shielded and bypassed. The underside of the
hood was equipped with a fibergaass blanket for heat control and the
blanket was faced with aluminum foil for radio frequency control. It was
grounded. Trucks must use something similar if they have spark ignition
systems.

The Corvette`s Delco radio only had medium wave AM and VHF FM reception.
Both were satisfactorily quiet. Screams during acceleration and sudden
stops were the only disconcerting noises.

Best regatrds, Richard Harrison, KB5WZI