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Old 25-11-2009, 07:58   #1
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DC Blocking Capacitors

OK, this is yet another SSB grounding question, but with a slight twist.

I intend to ground my SSB set up via the rather nice stainless bolts on the lead keel but don't want to have any possibility of stray DC so I'm planning to break the copper foil and insert a number of parallel ceramic caps by way of a DC block.

I've seen this method described somewhere else, but never any suggestions on what values to use.

I'm guessing this is not critical at all, but does anyone have any suggestions. I'm thinking 5 or 6 x 100nF 3,000V devices which I intend to permentaly encapsulate in resin.

Duncan & Joan Ellison
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Old 25-11-2009, 08:27   #2
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caps

To avoid making another DC ground to the engine via the HF/SSB radio copper ground strip, fasten the copper tape securely to an insulating piece of phenolic or to a terminal strip, cut a 1/10" gap across the tape, and solder several 0.15 uF ceramic capacitors across the gap.
[IMG]file:///C:/Documents%20and%20Settings/NSchwart/My%20Documents/Podjo/Grounding_files/mg_image011.jpg[/IMG]
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Old 25-11-2009, 08:39   #3
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Meant to add this picture.....
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Old 25-11-2009, 11:27   #4
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Quote:
Originally Posted by NealS View Post
To avoid making another DC ground to the engine via the HF/SSB radio copper ground strip, fasten the copper tape securely to an insulating piece of phenolic or to a terminal strip, cut a 1/10" gap across the tape, and solder several 0.15 uF ceramic capacitors across the gap.
As per Stan Honey's old Marine Grounding Systems aritcle for 'Practical Sailor'.

Grounding
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Old 25-11-2009, 12:25   #5
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NealS / Gordmay, thank you.

That was precisely the picture I meant.

For others following on, you have to read to the bottom of the article to get the exact spec for the capacitors. The size is about what I thought too, so that's comforting.

One thing puzzling me though is the voltage rating, the specified caps are only 100V rated. I'm sure when I've seen this done before much higher voltage ratings were used.

Duncan
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Old 25-11-2009, 13:40   #6
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The popular SGC-230 tuner has blocking caps built into the tuner. They use three .033 microfarad 630 volt caps in parallel and a 220Kohm 1 watt resistor also in parallel with the caps.

Eric
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Old 25-11-2009, 13:52   #7
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Thanks Eric, that tends to confirm my thoughts about a higher voltage rating.

Duncan
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