W2RU - Bud Hippisley wrote:
> It's clear from the original description of the TM-D700 problem that
> it's *not* alternator whine.
>
> However, with respect to alternator whine:
>
> I agree with the earlier comment that most of the easily available
> filters and chokes (such as from Radio Shack) are not going to do the
> job -- especially with the high current drains when a 50-watt rig is
> transmitting. What I've found really simple to implement for my
> various (Kenwood) 2-meter mobile rigs over the years has been to use
> the inductance of the filament winding of an ordinary 10- or 20-amp
> 6.3-volt filament transformer in series with the positive lead from
> the engine compartment. I then shunt the rig side of the filament
> transformer winding with an old-fashioned 100uf 50VDC paper
>
There are bulkhead, or feed through caps that will do this job
nicely...if you can find them. They are a coaxial capacitor and vary
from around a 1/2" to 2" in diameter and are several inches long (or
more). One I have has a flange around the middle with much the same
outline as a TO-3 case but much larger. The bolt holes at the ends are
about 1/4". I just saw the thing within the past couple of days. Now if
I could just remember where, I'd check it for make and model number.
IIRC the center conductor was drilled and tapped for #10-32
I also have (somewhere <sigh>) one that is about 5/8" in diameter and
about 1 1/2" long that have been used in my cars over the last 30
years. Where did I find them? I have absolutely no idea. Maybe a swap
some where along the line or I may have pulled them out of an old piece
of surplus back in the days when we'd already be past our first big snow
storm by this time of year. Used with the inductor I'd think the two
would be very effective IF it's something coming in on the power leads.
I would recommend keeping the power leads on the opposite side of the
engine compartment from the computer and well away from the alternator.
BTW when I ran into the low voltage caused oscillation it sounded just
like alternator whine.
73
Roger (K8RI)
> electrolytic to the negative lead. Of course, the leads for the
> primary winding of the transformer go nowhere -- they just get taped
> up. The whole assembly has fit very neatly up under the heat ducts of
> my dashboard in every car I've installed a 2-meter rig in. And it's
> all been from junque-box parts -- I didn't spend a penny!
>
> Bud, W2RU
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