How to pass a URL from one page to another

[ChurchMedia]

I need to pass a URL from a standard VB page to a page that I've written. I tried using this in the Global Start plug in:

$pageurl = "http://".$_SERVER['HTTP_HOST'].$_SERVER[PHP_SELF];

And then created a link in the navbar template that SHOULD look like this:

http://www.churchmedia.net/CMN/setpage.php?sp=$pageurl

With the $pageurl replaced with the VB page that it came from. But nothing -- instead I get this:

http://www.churchmedia.net/CMN/setpage.php?sp=

With no URL. Is there a better way to grab the URL and put it into a variable that can go into a link? Thanks!