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Generating a Radio Signal?

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roadkillguy

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Hello everyone, I know I'm brand new here but I've been trying to think of a way to generate a simple radio signal that could go at least 50 feet or so. One of my ideas is to simply have a clock signal amplified through a transistor amplifier circuit. Does this method seem plausible?
 
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MikeMl

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Why? Computer/electronics makers go to extraordinary lengths to keep signals from leaking out of their boxes. In spite of their best efforts, they some times screw up. As a ham radio operator, I hate it when I hear harmonics of my neighbor's burglar alarm SMPS power supply all the way across the 40meter band. Or the leakage from their computer, or CFL lamps, or ...

Why make it worse?
 

audioguru

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As a ham radio operator why are you still using AM modulation? Everybody knows that it picks up all kinds of interference. Use FM instead.
 

MikeMl

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As a ham radio operator why are you still using AM modulation? Everybody knows that it picks up all kinds of interference. Use FM instead.
I use FM on all bands above 28Mhz. International regs do not permit voice FM on most of our HF bands. Instead, we use SingleSideBand, and keyed CW, which rely on amplitude detection. We are allowed such a narrow bandwidth for voice modulation that FM at such low deviation has a much inferior signal-to-noise ratio in the presence of interference compared to SSB.

Non-voice digital modes in the HF bands do use FM, specifically multi-frequency shift keying.

The leakage from SMPS and computer clocks usually manifests as a whistle or tone (heterodyne) when listening to SSB or CW. It would do the same on NBFM. Only if you can use bandwidths like are used in the FM broadcast band (~75kHz) do you get impulse noise immunity and improved SNRR.
 
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audioguru

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FM receivers have a limiting IF. The limiting makes AM reception zero.
They also have a "capture ratio" where only the strongest signal is demodulated and another signal on the same frequency is ignored.

Airplanes still use AM so that a plane in trouble can break in with a "Mayday" call.
 

MikeMl

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...

Airplanes still use AM so that a plane in trouble can break in with a "Mayday" call.

Airplanes today still use AM today because historically, AM has been used since before WW2. There is an installed base of a few million AM transceivers, and it will never change now. As more channels are needed, the band has been divided into progressively narrower channels, just like on other VHF radio services. As the channel bandwidth gets <10kHz, FM loses any advantage over AM or SSB.
 

roadkillguy

New Member
Well, being that I'm trying to build this somewhat implies that I am in fact intentionally generating a radio signal... I'm not going to have the signal carry any sort of sound wave, so it's not am or fm. Instead, I'm going to turn it on and off to do morse code or something of the likes. But either way would a clock w/transistor work? I'm guessing it should based on your post...
 
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audioguru

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If you simply turn on a radio transmitter then turn it off with Morse Code then what do you expect the receiver to do? Produce silence followed by silence?
The receiver could have a circuit to turn on when it receives the carrier then turn off when the carrier stops. But it is prone to be activated by interference.
 

audioguru

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You should have a modulation that is analog or digital that is yours.
 

Tesla23

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FM receivers have a limiting IF. The limiting makes AM reception zero.
They also have a "capture ratio" where only the strongest signal is demodulated and another signal on the same frequency is ignored.

This is only true in the limit as the deviation gets very large. For all practical systems the rejection of interference and weaker signals is finite, and as Mike has said, vanishes for modulation indexes somewhere around unity.

Even if the interfering signal is itself AM, any interference added to the wanted signal will produce both AM and PM. If the deviation is very large the effect of the PM is reduced (but not eliminated), but it is not reduced if the deviation is small.
 
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