I set out wanting to capture the signal transmitted from my gate opener (pictured at  the very bottom) but the results are confusing so I am attempting to document what I did.

The first thing I I did was build a basic receiver in gnu radio to do the capturing shown here.

osmocom source: This an interface to our software defined radio (hardware)

• sample rate: 16M  ( our hardware can effectively sample between 8 million IQ samples per second and 20M because of my initially confusing results I upped it to 16M hoping it was a resolution problem.
• Ch0 : frequency: ( center frequency ):  300M  300mhz
• Ch0: RF gain: 0 this this controls a rx amp built into our hardware)

QT GUI sink:  ( just a way to out put our signal in the frequency domain )

the brown line is peak hold using this I estimated the transmit frequency to be ~ 300.2 mhz the blue spike at 300 is a gnu radio side effect which occurs at the center frequency.

The next step I assumed would be to attempt to “tune” and demodulate the signal so I built a another flowgraph for that:

• File source: ( just our IQ samples stored in a file)
• Throttle: This prevents gnu radio from sending data faster than 16Mps
• QT GUI sink : outputs the previous graph
• Frequency Xlating FIR FILTER ( was supposed to accomplish the fallowing) 
  • tune to our signal by downshifting captured spectrum by the difference between the center frequency and the tuning frequency
  • low pass filter the shifted signal with a cutoff of 50kHz and a transition width of 1Khz
  • decimate the outgoing data stream down to our working_samp_rate of 400kHz
  • XFF details ( how we do the above with this block)
    • Decimation:  int(samp_rate/working_samp_rate)
    • Taps: firdes.low_pass(1, samp_rate, filter_cutoff , filter_transition)
    • Center Frequency : freq-center_freq

Demodulation:( maybe this is where I went wrong?) : I am only really familiar with on off keying so  I use the so called “complex to magic” block to provide a high constant value when the carrier is present and a low ~constant value when the carrier is absent. 

The fallowing shows but the input provided to complex to mag and the output afterwards: 

So Looking at things in the time dimension demodulated or not I don’t see anything I would recognize as digital maybe a nice square wav? So I suspect that at least 1 of the fallowing things are true.

1. My gate opener is broken
2. my gate opener is not digital
3. my gate opener does not use on off keying?
4. Something else?