A radio show that empowers the audience to go to a web page and register, vote, or fill out a survey is a survey bias. When random people are self-selected the survey will most likely be biased because the resulting sample will represent those who have strong opinions. Other people won't participate, and other would probably not even listen to that radio station. The type of poorly design survey, in this case, is a "Voluntary Response Sample", accompanied with "Response Bias" and "Nonresponse Bias". There could also be "Bias in the wording of questions" because the way the radio promotes this survey indicates how many people from the audience will actually participate.
