When you are pitching to a person in order to get on national public radio you probably will either do it over the phone, mail, or email. There is a right way and a wrong way to go about this.

If you're pitching to the person "live" on the telephone, it is quite possible that they will say, "Well, let me look at the material" or "Do you have some material that you can send to me?" And if that is the case, and you sent them by mail, you should not just count the number of days it takes to land on their desk. You should give it a few days after that so that they actually have time to look over the material, crack the spine of the book open. Also, if you sent an email or something by mail, you should not assume that they are going to contact you if they're interested. You should initiate that contact. If a day or two goes by and you have not had a response to an email, it's perfectly appropriate to send them another one, so long as you have a little fresh information to supply.

You can find a lot more helpful information like this in How to Get Booked on National Public Radio.
http://101publicrelations.com/nationalpublicradio.html?utm_source=prideas&utm_content=npr