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8

Modern digital systems communicating over HF (aka short-wave) are legal in the US and practical, and in fact one such system is in routine daily use. Have a look at the Winlink system. (The official web site is here, but the Wikipedia article provides a better general overview.) It uses the PACTOR and WINMOR modes. Winlink messages are formatted as email;...


7

So, the bandwidth argument is the dominant one. You need to incorporate the full Carson Bandwidth in your channel spacing, not only the frequency deviation! As explained in my answer to your previous question, that must be significantly larger than the bandwidth of the same audio signal in AM. Aside from that, as always in Ham usage: historical reasons. If ...


3

A lid where a magnet attaches is made out of iron. Iron is a good conductor. You're trying to build an antenna in a place which is especially well-shielded against radiation. That will be very very difficult. Omnidirectional from under a manhole cover means "in the earth". If that isn't dry, then there will be little signal there. Yes, radio waves can ...


2

The sidebands generated by frequency modulation are not as simple as those with AM, as their distribution is affected by both the amplitude & frequency of the modulating signal. A normal VHF station with a "max deviation" of 50 kHz will actually deviate 50kHz above & above the unmodulated carrier frequency, for a total bandwidth of 100kHz. ...


2

In general, the length and shape of an antenna has a profound effect on the amount of power the antenna makes available to the receiver. Matching the impedance of the antenna system to that of the receiver ensures that the receiver can take advantage of the power that the antenna system delivers. At the low frequencies in which you are interested, I would ...


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