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C3 is a DC blocking capacitor for the RF input.
It is intended to be an open circuit to DC, but at 27MHz it should be of low loss.
1000pF is about 6 ohms at this RF.
but 2000pF is 3ohms, and might give slightly better input vswr or less loss.

You may also notice C1 is 15pF, which is used to couple a small amount of RF to turn on transistor which keys relay. 15pF is like 400ohms to 27MHz, so only a small amount of energy will pass across it.

[QUOTE="dudmuck, post: 201911, member: 3904"] C3 is a DC blocking capacitor for the RF input. It is intended to be an open circuit to DC, but at 27MHz it should be of low loss. 1000pF is about 6 ohms at this RF. but 2000pF is 3ohms, and might give slightly better input vswr or less loss. You may also notice C1 is 15pF, which is used to couple a small amount of RF to turn on transistor which keys relay. 15pF is like 400ohms to 27MHz, so only a small amount of energy will pass across it. [/QUOTE]

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