Of course Charlie, the best way to improve your voice is to use it and get some real experience. 99.9% of the pros didn't learn their craft from a book .. at some point you've got to put the books down and get your feet wet/hands dirty. It's the only way you will ever find out if you even have a radio voice.
Many people have found my book very useful as a starting point in making it as a radio presenter/broadcaster. My book's details are as follows:
How To Get Into Radio, starting your career as a radio broadcaster, by Bernie Simmons [ISBN: 1-85703-143-1] published by How-To Books.
It was published in 1995 and was in print until 2003, which is a long run for this type of book. Your local libraries will be able to get it for you, and if they tell you it's out of print, tell them to request it from The British Library. I'll tell you now, that the thrust of the message of the book is along the lines of
stop thinking and talking about and put some headphones and get on with it and learn your craft!
If at any time you want to contact me privately for any help at all, just hit that PM button or email me.
Good luck - you won't need it!