I was all set to give my regular snarky "use a better Podcast app" reply, because I really strongly dislike the native one, but I was pleasantly surprised to see it handle this particular case correctly (ish).
The link to use is "http://www.summahistorica.com/podcast/rss.xml" - it seems to work. (The other podcast apps I have on my phone didn't find that particular podcast either - so I can't (fairly) blame the native app's catalog for not knowing about it.)
(Also, if you like history podcasts, check out "The Memory Palace" (
The Memory Palace) - it's in the native app's catalog - very short (2-5 minutes, usually) semi-monthly essays about odd little bits of non-mainstream US history. Well worth the free price.)