As the other commentator has stated, the vast majority revenue for PBS is by member contributions, donations of broadcast rights, and distribution fees. In 2018, members gave $197,552,000 while public grants and contributions were $105,336,000. A quick look at their revenues suggests that public grants and contributions only make up ~16% of revenues for PBS. Without asking for $60/year for Passport (which you also get if you're a member) they wouldn't be able to do most of what they do.
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