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3

I get the impression that this answer is too long for many people, so here's the abstract: I presume your goal is to make a system that will automatically record a message when someone calls a particular operator on HF SSB and the operator doesn't respond, like an answering machine. Also the system will alert the operator to an incoming call for him or her. ...

1

You might consider looking at packet radio. It allows for this kind of message passing to reach recipients similar to BBS-style messages or email. Similarly winlink is worth checking out. Neither of these are exactly the point-to-point alert-style you mention above, but both are implementable on a RPi which can be scripted to have a klaxon or spinny light ...

0

After reading this question a few times, I think I have a good idea what you are asking. I am not familiar with the transmitter or receiver you mention, but you say they use AM. Using an AM transmitter, you can not easily (I mean, I guess it might be technically possible if you can vary the frequency of the carrier accurately, extremely quickly) generate FSK,...

2

A low-pass filter is one way to do it. Due to the interpolation done in the repeat block, you are representing a symbol with 1000 samples, and your sample rate is 2 million samples per second (the samp_rate variable). So your square wave has a frequency of:  \require{cancel} {2000000\ \cancel{\text{samples}} \over \text{second}} {1\ \text{symbol} \over ...

0

I want to mention that the technique described at the end of the accepted answer can be seen very clearly in the LuaRadio documentation: https://luaradio.io/examples/ Each of the examples defines a variable tune_offset, whose value is slightly larger than the bandwidth of the desired signal. In the first example, which is an FM receiver, the bandwidth of ...

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