In our first couple papers on concurrent code spread spectrum (back before I coined that term) we mentioned how perhaps the ideal waveform for our system would have been from a spark gap generator since what we ideally wanted was high-power, short-duration extremely wideband noise pulses (white noise from DC to daylight that was then on-off keyed).

For simplicity, the radios that we flew out at China Lake just keyed an unmodulated carrier at our assigned frequency and it turned out to be extremely jam-resistant even though the jammer folks had our waveform information and our spreading code and all of our best thoughts on how best to jam the signal. They still had to get up to about 75 W before they shut down our comms even though we were transmitting at an average power of about 1 mW. Later demodulation software was able to successful recover all of the data from the recorded waveforms all the way up to their 150 W maximum output power and our best estimate is that they would have had to go to something north of 300 W to jam us.

 

UWB is usually (I think) referring to impulse-based radio, also known as time-hop spread spectrum although I don't think that term is very widely used.

It's similar to chirped spread spectrum. https://en.wikipedia.org/wiki/Chirp_spread_spectrum

 

It's similar to chirped spread spectrum. https://en.wikipedia.org/wiki/Chirp_spread_spectrum

If we had gotten to go out to China Lake the following year, using chirps would have been on my list of waveforms because our hardware was limited to about 1 W of peak power and I wanted to get more energy into each of our chips and using chirps seemed like a very viable idea to increase the energy an order of magnitude or so. But it would have also given the jammer something more to go after, so it would have been real interesting to see how the scales tipped on that one. But the big thing on our list was to use Golais codes, although personally I felt that we were opening a pretty big door for a jammer that wanted to really put in some effort.

 

If we had gotten to go out to China Lake the following year, using chirps would have been on my list of waveforms because our hardware was limited to about 1 W of peak power and I wanted to get more energy into each of our chips and using chirps seemed like a very viable idea to increase the energy an order of magnitude or so. But it would have also given the jammer something more to go after, so it would have been real interesting to see how the scales tipped on that one. But the big thing on our list was to use Golais codes, although personally I felt that we were opening a pretty big door for a jammer that wanted to really put in some effort.

The Russians were using a early form of chirp over-the-horizon radar on HF bands when I was in. That signal raised holy hell with long distance HF links we used for encrypted communications. We suspected it was also used as a jamming station because it would often move frequencies to match ours but that could be because they were using the same ionospheric conditions to see distant locations that we used to communicate with.
https://en.wikipedia.org/wiki/Duga_radar

 

Wow..wicked cool!

 

Making your FM signal appear on several different FM channels can be simple in principle.

Feed your transmitter's output to one input of a broadband RF mixer. Connect a square wave signal with its frequency being the same as the desired channel spacing. Connect the mixer's output to the antenna.

For example if your transmitter broadcasts at 100 MHz. With a 2 MHz square wave input your transmitter can be heard at ...90 MHz, 92 MHz, 94 MHz, 96 MHz, 98 MHz, 100 MHz, 102 MHz, 104 MHz...

The amplitude of the signal will decrease as the difference between the transmitter's frequency and the received frquency increases. This can be compensated within limits.

A sine wave can be used to drive the mixer if the amplitude is greatly in excess of the intended signal -this is referred to as over-driving the mixer.

 

So what you are saying is that if someone samples and captures a portion of the RF spectrum centered at, say, 1000 kHz with enough bandwidth to capture, say a 400 kHz wide signal, that it is not possible for them to turn around and retransmit that signal centered at 1000 kHz and have the resulting signal be a reasonably faithful representation of what was in that 400 kHz portion of the spectrum?

With enough DSP horsepower, it is possible to do what you have said. I was answering in context of the OP's original question - taking an MP3 signal and trying to transmit it onto more than one receive frequency with one transmitter. I was unaware that the OP had all this DSP power at his disposal! But he can do it without DSP - simply:

1) Generate an FM signal with his MP3 at the first frequency he wants to receive.
2) Generate the second signal at the second frequency, then mix that with the offset from f1 to f2, then filter out the undesired sideband, then add it to the signal from the first freq.
3) Repeat step 2) for all the other freqs that he wants to receive,
4) Modulate a transmitter with the resulting waveform from step 3) and VIOLA! he has accomplished his goal!

 

I don't see why the TS can't just set all the presets on his car radio to the one frequency his transmitter is set to as his goal just seems to be to fool his passenger.

Les.