Iframe Window.location As A Global Variable - String

I have come up with form which pulls membership id, allows checkbox selections and commentry (custom feedback). The final piece that needs to be captured is the iframe's url. Now the content in the iframe is content produced by (madcap) flare.

I need to capture the window.location of the iframe url and pass that onto the asp.net masterpage. The iframe is also located in a content page. The iframes content is controlled by it's own TOC. I have added a script to this output so that each time the content (page) in the iframe changes the script alert's me of the new URL of the page just clicked/opened (this is the information I need passed as a variable).

Here is the code producing the desired alert output (page url).

Code:

The above produces the output I would like to capture (but instead of an alert output, I require this as a string) which will allow the insertion into my form as the final piece of information required.

I am not sure how I can convert or catch the output. Of course I would not want to use the alert function everytime the page changes, but would like to have the window.location bound to a string which I can then use when inserting into my codebehind sql statement.

All the captured data is being inserted using vb.net into a sql table.

I just need to make that content page > iframe (window.location) a global variable that my masterpages codebehind can inject into the INSERT SQL statement.