3 ms·
"AM" is the modulation scheme. A more accurate name for this radio service is used in Europe, "middle-wave". The modulation scheme is not the reason for propa
by lebuffon 2y ago
"AM" is the modulation scheme.
A more accurate name for this radio service is used in Europe, "middle-wave".
The modulation scheme is not the reason for propagating around mountains and bouncing off the ionosphere at night. The reason for that behaviour is the low frequency used. 540 Kilo-herz to ~1700 Kilo-herz.
(I was told once by a young engineering colleague that 1,000 Khz was not RF.
:-))) )
So the question is valid. FM could be used in the "middle-wave" band.
It would reduce noise but might suffer more when bouncing off the ionosphere at night. (I have read this but never heard FM bounced)
The reason FM is not used in the middle-wave band is legacy regulation not technology.
- ikiris 2y agoFm also takes 10 times the bandwidth of am of that spectrum. The blocks are where they are for a reason.
- lebuffon 2y agoFM takes whatever bandwidth you allow it. The harder you hit it the wider it goes. The limiting factor is when modulation exceeds the bandwidth of the receiver, it clips very badly. Narrow band FM is used for aircraft. police, fire, amateur radio communication and since 2021 it's even legal for CB radio in the USA. It's deviation is limited by law to about +/-2.5KHz, from centre frequency. Setting up the modulation depth on an a broadcast FM exciter, I have used a spectrum analyzer and Bessel function information to make sure it was legal.
- hilbert42 2y ago" (I was told once by a young engineering colleague that 1,000 Khz was not RF. :-))) )" I've alluded to this elsewhere. As I mentioned, RF/RFI and spectrum management subjects have been downgraded or reduced in electrical engineering courses just about everywhere so it's little wonder we've problem.