[scissors]

As far as i know Calibre can'y go to a site and fetch a mobi file.
what it does is take (scrape) websites and throw out everything except the article.

if you go to http://www.tennessean.com/section/digital

the list of RSS feeds are at the bottom of the page
these URLs are what you add to the basic news recipe

example

Spoiler:

class AdvancedUserRecipe1387642952(BasicNewsRecipe):
    title          = u'test'
    oldest_article = 7
    max_articles_per_feed = 100
    auto_cleanup = True

    feeds          = [(u'top news', u'http://www.tennessean.com/apps/pbcs.dll/section?prof=2275&Category=profilerss&mime=xml&nocache=1&rsstitle=TOP%20NEWS')]

Hope that helps, sorry that's all i can offer.

I recommend you read,

http://manual.calibre-ebook.com/news...asicNewsRecipe