A bit about #hamradio for non-technical people explaining why it can be fun (personal view).

Thread #2: Frequency Bands.

Remember the quoted thread talked about Medium Wave and VHF? There are all sorts of ways of dividing up the Electromagnetic Spectrum. / https://twitter.com/DrAlanRobinson/status/1263788957369843712

/ You can look at the whole thing in terms of frequency from the ~1 Hz (1 vibration per second) end through all sorts of stuff including radio waves and light waves and X-rays and Gamma rays and beyond.

The radio wave bit can be divided into bands by "decades" of frequency /

/ for e.g.

LF (Low Frequency) 30 kHz - 300 kHz
MF (medium ..) 300 to 3000
HF (high) 3MHz to 30 MHz
VHF (very) 30 - 300 MHz
UHF (ultra) 300 - 3000 (3GHz)
SHF (super) 3 GHz - 30 GHz
EHF (extra) 30 GHz - 300 GHz /

/ MF contains the good old Medium Wave broadcast
VHF contains the FM broadcast band and aircraft navigation and communication systems & other stuff
HF contains a whole *mix* of things & is one I want to describe why it's interesting. /

/ Radio waves, like light, travels in straight lines unless something bends or reflects them. So if I transmit radio from my home on the South coast of the UK, most of the power goes straight off into space. Only a fraction goes out sideways to be picked up by people /

/ say 10 miles away. After that, the curvature of the earth and local obstructions means that my signal can't be "seen" by anyone.

BUT. Up in the atmosphere is a thing called the ionosphere. It's called that because it contains ionised gas; the sun's energy rips electrons /

/ away from atoms leaving them electrically charged. And electrically charged things vibrate in response to radio waves. And vibrating, electrically charged things *produce* radio waves. So my signal sets the ions & electrons wobbling, and they make a copy /

/ of my signal and some of this comes back down to earth. This means that my signal can be heard thousands of miles away (but *not* hundreds of miles away, because it is "skipping" over these distances high above the ground). /

/ What makes this interesting is that the ionosphere is driven by the sun, the sun has weather and climate, and the behaviour of the ionosphere varies with time of day, the sun's weather, and the frequency being used for transmission. /

/ Lots of history that I won't go into here but "Radio Hams" have been given special frequency bands, many of which sit in the "HF" range. Each one of these bands has its own characteristics in the way that it interacts with the ionosphere. /

/ So for example, signals on the band at 1.6 MHz get absorbed during the daytime, but travel well and get reflected down at night. At 28MHz, most of the time conditions are "Line of sight" but in summer daytime signals can go thousands of miles. /

/ There are bands in between at 3.5, 7, 10, 14, 18, 21, & 24 MHz plus a few others. And they all have their particular characteristics and pros and cons - pretty much sliding gracefully from the characteristics of the 1.6 MHz band to those of the 28 MHz band /

/ with mixed characteristics in between.

As I said on the other thread, higher frequency means smaller antennas. Smaller antennas means that hobbyists can put them up higher and design more efficient ones than if the are big, heavy and bulky. /

/ So there's a lot going on just in the choice of frequency band and antenna to keep a radio ham interested. Add to this the fact that all radio hams worldwide are allocated a unique "callsign" (mine is G1OJS with the G indicating that I'm based in England) and /

/ this also provides a lot of interest for us autistic types who love databases and logs and categorising information. So for instance I now that since I set up my station in my current home, I've made contact with other hams in over 200 countries. I can set myself /

/ challenges, such as "Make contact with someone in all countries in Europe using just the 28 MHz band".

If you want to look at my "log" of contacts, it's online at http://qrz.com  . Just enter "G1OJS" in the query box and click on the Logbook tab when my entry comes up/

/ That's the end of thread number #2!

Hope you found that even a little bit interesting!