Difference between revisions of "Talk:3 Meter FM Broadcast Radio"
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FM broadcast 3 meter band | FM broadcast 3 meter band | ||
| − | AM broadcast 300 Meter band | + | AM broadcast 300 Meter band ??? or 200 Meter band |
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| + | AM (.5-1.7 Mhz or the 200 meter band) | ||
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| + | AM was developed before FM and was technologically easier to develop. For AM all you needed was a crystal or diode detector and a tuned tank circuit, FM required ratio detectors and limiters and is far more complex. Noise is inherently Amplitude in nature, an FM receiver rejects amplitude impulses and only detects changes in the frequency domain. A peculiarity of FM is called the "capture effect", which means the strongest signal captures the receiver and weaker signals cannot be heard in the background. This is not so in AM which allows for other signals to be heard over a stronger one. For this reason it is used by pilots so that all aircraft traffic can be heard or detected when two or more pilots attempt to communicate at the same time. No doubt this has saved many lives. | ||
| + | |||
| + | Radio frequencies are the same as keys on a piano, if you strike middle C thats all you hear. It doesn't cause other frequencies to resonate, other than the ones that are harmonically related. 140 Mhz and 141 Mhz are not harmonically related. 140, 280, 420 Mhz etc. are related, but in a properly designed transmitter those higher harmonics are filtered or trapped out so as not to cause interference to other users. | ||
| + | |||
| + | == legal am == | ||
| + | |||
| + | Part 15 low power license-free broadcasting FAQ | ||
| + | legal unlicensed broadcasting | ||
| + | as permitted in the US under the Part 15 rules | ||
| + | with an emphasis on the AM band | ||
Latest revision as of 22:36, 29 July 2015
FM broadcast 3 meter band
AM broadcast 300 Meter band ??? or 200 Meter band
AM (.5-1.7 Mhz or the 200 meter band)
AM was developed before FM and was technologically easier to develop. For AM all you needed was a crystal or diode detector and a tuned tank circuit, FM required ratio detectors and limiters and is far more complex. Noise is inherently Amplitude in nature, an FM receiver rejects amplitude impulses and only detects changes in the frequency domain. A peculiarity of FM is called the "capture effect", which means the strongest signal captures the receiver and weaker signals cannot be heard in the background. This is not so in AM which allows for other signals to be heard over a stronger one. For this reason it is used by pilots so that all aircraft traffic can be heard or detected when two or more pilots attempt to communicate at the same time. No doubt this has saved many lives.
Radio frequencies are the same as keys on a piano, if you strike middle C thats all you hear. It doesn't cause other frequencies to resonate, other than the ones that are harmonically related. 140 Mhz and 141 Mhz are not harmonically related. 140, 280, 420 Mhz etc. are related, but in a properly designed transmitter those higher harmonics are filtered or trapped out so as not to cause interference to other users.
legal am
Part 15 low power license-free broadcasting FAQ legal unlicensed broadcasting as permitted in the US under the Part 15 rules with an emphasis on the AM band
