Dual tone multi-frequency signals are commonly used in the creation of phone tones, and in
this example I'm going to show you how to easily create one using a Trueform generator.
I have a set of speakers connected to my generator, and in this video you'll be able to hear
the dial tone signal that I'm creating as well as the noise that I'll be adding to
the signal in the second portion.
In order to create this dial tone signal which should be familiar to most of you in the U.S.,
we have to set up two different frequencies. So the first frequency is going to 350 hertz,
so I'm just going to change that frequency to be 350 here three, five, zero hertz.
And then I'm going to change the amplitude to be a little bit bigger so it can drive
my speakers a little bit better, and then that's all it is to create that base
350 Hertz.
In order to create the dual tone signal, I actually have to go to this modulate button
here and change my modulation type from the default A.M. modulation over to this Sum modulation,
which is a unique feature of Trueform generators as well, and I'm going to turn on this Sum
amplitude, change my amplitude to be 100% added together. That way I can actually add
the full signals together. And then I'm going to change the Sum frequency to be the
second 440 Hertz. So let's actually do that real quick.
And that's really all there is to creating that modulated signal. So in order to do that,
the last step I have to do is turn on modulation, and here you'll see a graphical representation
of that modulated summed signal between those two frequencies.
So now all I'm going to do is turn on Channel 1, and hopefully we'll hear some dial tone
signal. All right. That's kind of annoying so let's go ahead and turn that off. So
it's real easy to create a DTMF signal. However, let's go ahead and take this another
step and do another signal on top of this DTMF signal.
If you're a test engineer, you're going to actually want to maybe add some noise to
this signal, or potentially add in a four-tone signal together as well. So let's actually
create and add some noise to our dial tone signal that we have right now.
So in order to do that, I'm going to press this Channel 2 button, and go back to waveforms
for Channel 2, and I'm actually going to get a noise signal selected. And the bandwidth
right now is defaulted to 100 kilohertz, which is beyond most people's hearing frequency,
so let's actually just change that to one kilohertz so we can actually hear the noise.
And then for the amplitude I'm going to actually select two volts just so that it'll
be obvious to you when you listen to it that there's noise coming over on the speakers.
So now in order to combine Channel 1 and Channel 2 and get a noisy dual tone signal, I'm
actually going to go to Channel 1 and dual channel, and then this button here called
combine. So Channel 2, combine with Channel 1, so it's going to combine those and output
that on Channel 1 now. So let's go ahead and listen to what that's going to sound
like with a noisy signal. Hopefully you guys can hear this.
So to my ears it's very obvious that there is a lot of noise on that dial tone signal now, but let's take another
listen.
So with that combined functionality, you can actually create three tone signals or four
tone signals. All you have to do to create a four-tone signal is create a dial tone multi-frequency
signal on Channel 2 repeating the same steps that we had on Channel 1, and then use that
combined feature again to create up to a four-tone signal.
So not too bad, and again, this is a feature that's only available on Trueform generators.