Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_18536769_1 (call_sign VARCHAR, owner VARCHAR)
### Question:
When vista radio is the owner how many call signs are there?
### Answer:
SELECT COUNT(call_sign) FROM table_18536769_1 WHERE owner = "Vista Radio"