If you aren't interested in transmitting then you need to look for a wideband scanner. I started off with a Standard AX700 from EBAY, I like it and it's a good unit, I still use it but they are very old hat now. I progressed to a Uniden Bearcat handheld which is great for general scanning and airshows (but not particularly sensitive). I also have a Plessey TRP8255 as I like old military stuff. Oh and I made an airband reciever from a kit.
I would suggest sticking with VHF to start with as it's much easier 2meter and 70cm is where most activity seems to be. HF (1Mhz to 30Mhz) is a bit more complicated and you usually need space for a good antenna, mine runs 20metres down the garden (longwire antenna). My VHF antenna by comparison is only about 50cm long. You can easily make your own or buy one, there are many different types.
Just re-read your post, for worldwide communication you need HF (High Frequency), it's not so easy and you need usually space for a big antenna. The lower the frequency the bigger the antenna. For example 7MHz has a wavelength of 40metres your antenna is going to be 20metres long (half wavelength) or 10metres long (quarter wavelength) From the UK the best I've managed so far is Russia and Canada.
I would suggest sticking with VHF to start with as it's much easier 2meter and 70cm is where most activity seems to be. HF (1Mhz to 30Mhz) is a bit more complicated and you usually need space for a good antenna, mine runs 20metres down the garden (longwire antenna). My VHF antenna by comparison is only about 50cm long. You can easily make your own or buy one, there are many different types.
Just re-read your post, for worldwide communication you need HF (High Frequency), it's not so easy and you need usually space for a big antenna. The lower the frequency the bigger the antenna. For example 7MHz has a wavelength of 40metres your antenna is going to be 20metres long (half wavelength) or 10metres long (quarter wavelength) From the UK the best I've managed so far is Russia and Canada.
