What Does This FFT Mean?

[petecal]

I am in the process of implementing a "I've fallen and I can't get up" button for my wife.
I plan to use this button.
SOS Button

Using my SDR and GNURadio I found the following Scope Plot and FFT plot. The green FFT is the one that counts. What do the two peaks mean? It looks like one peak at 431.4 MHz and one at 436.4 MHz.


I bought some of these XMitter/Receiver pairs
433 MHz xmitter+receiver
and experimented with a square wave pulse train of similar pulse widths. This is what I get. Only a single peak in the FFT at 433.9 MHz.


I wonder how to properly receive the SOS button

 

[a417]

Please be careful making something that can be used in times of emergency.

You will not be able to live with yourself if your homemade contraption fails and a loved one dies.

[/soapbox]
You have peak hold on one of them, and not on the other. Quickly looking at it, I would think there are different transmissions modulations being used between the two devices, and that is why they are showing different FFT plots.

 

[petecal]

The green trace is the one that counts. I just couldn't click enough "stops" to freeze what counts.
The green trace is what I see when I press the button on the SOS. Does that mean the SOS is putting out two frequencies?
It seems to use a 433 SAW.

[soapbox]
I have it covered.
[/soapbox]

 

[AK9R]

Using my SDR and GNURadio I found the following Scope Plot and FFT plot. The green FFT is the one that counts. What do the two peaks mean? It looks like one peak at 431.4 MHz and one at 436.4 MHz.

If the radio is transmitting some sort of frequency shift keying (FSK) signal, you will see two peaks. However, a frequency shift of 5 MHz sounds awfully large.

Also note that if you are transmitting in the 420 to 450 MHz range in the U.S., you need an amateur radio license. The 435.0 to 438.0 MHz sub-band is for amateur radio satellites only.

 

[petecal]

The device creating the signal is a commercial button so I don't know about licensing:

The circuit board has this can on the back side.
The datasheet says it is a SAW. I think it is a fixed frequency. Can Datasheet

The circuit board looks like:


If the can is a fixed frequency I don't know how they would shift the frequency for FSK.

In my original post the top image is the detected pulse train when tuned to 433.9 MHz.

So I am still thinking about this.