这是一个一般疑问句,如果看不懂的话,可以将它变为一个陈述句：this is the man that you want to have repair the radio for me.从that引导的定语从句开始看,want(想)是个动作,have repair the radio for me（为我修收音机）也是一个动作,两个动作连接再结合want的用法,肯定中间需要to.另外,在have repair the radio for me少了一个宾语him,整体来看应该是have him repair the radio for me,但因为这是一个定语从句就把him省了.总之,后面的句型就是sb want to do sth,这里的do表示have him repair the radio for me.