Quote:
Originally Posted by Electronic M
 Okay, really basic radio theory lesson time: Carrier wave = the radio frequency sinusoid that travels through space and normally carries information of some type, Modulation = modification of carrier to place information on it. Un-modulated means no modification of the carrier sinusoid is made.....Just an RF osc. (and probably a power amplifier) randomly radiating power out into space for no good reason.
Types of modulation include CW (turning carrier on and off to represent information normally in the form of Morse code), AM (changing the strength of the carrier instep with a signal that is normally a sound or video signal), FM (changing the frequency of the carrier instep with the signal), PM (changing the phase of the carrier instep with the signal...an integral/differentiation relationship exists between PM and FM signal encoding), QAM (Google it! most common example is color sub-carrier modulation scheme in NTSC TV), and various forms of digital modulation that I don't care to regurgitate, enumerate, and explain.....
As for how common un-modulated carriers are on shortwave...I can't say. It's been a few years since I was a regular SW listener, and even then it's hard to know since many radios (including my favorite SW set) lack a good signal strength meter, and unless the meter is looking directly at RF carrier strength you really have no way to know of their presence with a normal radio unless the band around them is VERY noisy...And even that is not a guarantee of their presence.
The only surefire way to find them is to plop down big bucks for a spectrum analyzer and use that to tune a radio to the frequencies of noticeable carriers....Or attach a measurement device to a TRF radio and learn the difference between atmospheric background noise and carrier waves.
If you don't know how the beast works your not an electronic technician, but a mechanic/parts swaper. |
I have a basic running knowledge of how radios work but as far as why they do some of the strange things they do sometimes that I don't understand (after all I'm going to school for computer repair not electronics repair, seeing as electronics repair is more or less a dead artform since everything is more or less juts throwaway now, because I was born about 3 decades too late for electronics repair classes of any sort and I mainly dabble with radio and record player repair as a side hobby.)
Also there still hasn't been any definitive answers given yet as to why the tuning eye tube on my radio would be more sensitive on the Shortwave band than on Broadcast (AM) band, especially seeing as I've figured out that the tuning eye socket is getting the proper voltages its supposed to have but yet it barely responds on the AM Band but responds extremely well on the SW Band.