All,
I’ve just installed my new Icom 2730H in my BMW X5 SUV. Despite the fact that
the battery is in the back on BMW and wiring direct (please see this month’s
issue of QST), I still have receive audio alternator whine.
This has been an off and on issue with a number of vehicles over the years.
Because of the audio frequencies that we’re dealing with, we need an iron-core
transformer to give us enough choking. Finding these in a package that can
comfortably handle 20-40A for mobile operations is darned difficult.
Back in NC, I knew a guy who used to service police cars. He told me about the
Motorola filters. I’ve tracked down some on eBay where the seller has found a
warehouse of them NIB!
http://www.ebay.com/itm/301163766083 <http://www.ebay.com/itm/301163766083>
You’ll need to replace the electrolytic capacitor as the one inside has likely
dried out. Any value close will be fine. There are also diodes to help suppress
the reverse kick from starting the engine.
The connection MUST be as follows:
(battery + terminal) -> (fuse) -> (motorola uber filter) -> radio.
In the event that the filter clamps down, we want the fuse to blow to prevent a
fire.
***
I have been using this setup in my other vehicle for years and my radios love
it.
Show your radio some love. Give it clean DC and it will make you happy.
Bill, N4HPG
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