The President of the United States has extensive use of the airwaves in an emergency and the zombie Apocalypse didn't knock out satellites nor I'd think emergency transmitters at radio stations which IIRC by law have months of battery life to keep transmitting in an emergency.
They're beyond the 'months' point now, though. Even assuming Rick was only in the hospital a few weeks total, they were somewhere in summer at the point Rick was there (temp was over 100 at one point), lasted the winter, and are now in spring of the following year.
BTW, now that I'm thinking about it - why wouldn't Rick and group us car GPS systems to navigate to safe havens instead of using maps?
Could have found one, but it's easier to plan with a map laid out. Plus can update to NEW info, make notes, etc. GPS will get you there, or at least would have based on pre-disaster routes, but harder to look at and plan.
Plus, satellites aren't permanent, they require upkeep and maintainence. many may have fallen out of orbit, or at least become mis-alligned and no longer work properly. That's likely more than a few month period to decay like that, but the system WILL fall apart without repositioning and adjustment.
I'd think that slow moving zombies would find it difficult to overtake any large military installation based on the amount of fire power they have versus the threat
Yep, logic breaks down zombie outbreaks pretty fast. Which is why most places just focus on a small area, and right at the beginning of the outbreak when people don't know how to act, not to try and save bitten friends, etc. In "reality", zombies would find it tough going, they're not smart/fast/well armed, and their food source is also a better predator than they are.
Also, what about nuclear submarines, aircraft carriers and even the International space station?
Space station has similar issues to the satellites. Will eventually come down, plus needs supplies to keep people alive. The current crew may stay up a while to try and see what's going on, but eventually has to bail out and come home, or die there.
Subs, carriers, and the like would be ok for a long while, supplies are the issue. Nuclear means fuel isn't an issue, just risk of coming ashore for supplies. You'd lose some to taking bitten people onboard, but based on how zombies act in TWD world, they're not patrolling the ocean floor like World War Z, so boats should be ok. WWZ was better in general with showing things go to shit, but at least not having EVERYTHING disintegrate. And maybe it hasn't in TWD, and we're just focused too tightly on our group?