Dear OgreVorbis,
Thank you very much for your detailed reply, I really appreciate it.
Regarding FM, I've pretty much discarded that option as all of the FM frequencies in my city are taken and authorities are really strict on that.
On the other hand, AM is pretty empty yet available everywhere (cars, most radios...). I live in an apartment block, so the only place I would be able to set up a MW antenna would be on the rooftop, so no buring ground sticks (those metal things, sorry for the lack of vocabulary) and space could be a little bit of a problem. How big are we talking about? Would a 1/4 dipole in an inverted vee work?
I've considered shortwave and I've talked with Stretchyman about it. I don't really have the budget to spend on a powerful transmitter, so I'd be TXing low power with one of his transmitters (I'm still learning about building one and I wouldn't want to mess it up, so building one myself is not an option, currently), meaning that I maybe wouldn't be able to reach very far, yet also wouldn't make it locally due to the skip.
What do you recommend? I'm still doubting about which route to take.
Again, thank you so much for your help.
Best regards,
Diego
In terms of antennas:
For SW, an inverted V is probably my favorite because it doesn't take up too much space and only requires one support. The skywave propagation with them is also pretty good.
For MW:
I've tried a full half wave inverted V - this was huge and the local coverage was poor, but I was able to tune into myself from an SDR about 500 miles away. (This was with 300W on 1710). The local coverage was only 2 miles interestingly.
Isotron - the worst
Long wire - second worst
1/4 wave ground plane - the best (this was temporary because I had to use a balloon to raise the wire)
If you want local, you'll need a vertical antenna. I don't know how high your block is, but maybe hanging an antenna from the roof instead of trying to fit it on top would be better. The ideal situation would be if you were on the middle floor of a tall building because then you could put the center of the dipole out the window and have one leg run up to the roof and let the other hang to the ground.
EDIT: If you decide to go with MW, you're likely going to need an antenna tuner. Unless your antenna is in the middle of a field, the surrounding objects will make it not resonate at the proper frequency. There is a formula to calculate the length, but you'll find that on MW the calculation ends up being so much different than the actual length the antenna needs to be. With shortwave, as long as you have an SWR analyzer, you won't need a tuner because generally, you can just cut the ends of the V until you get it perfect.
I also really recommend that transmitter I linked to in my other post. It will work on both MW and SW, so you won't need to buy another transmitter if you change your mind. You'll need an amplifier for it though because it only makes 1mW.
You should also check out VOACAP btw. You put in your location and a few other parameters and it will give you a theoretical coverage map. You can select the frequency and do it again to see the difference in propagation.