meynarddanam reacted to chicken in [POTM] dAISy - A Simple AIS Receiver
Ah sorry, I was looking at the original schematic posted in this thread.
The 220pF is an AC coupling cap. It's there to avoid any DC from the antenna port to get to the radio. Anything on the order of 100pF should be fine. 220pF was what I had at hand.
Here's a good explanation of coupling caps: