DTR radios are invisible on the spectrum analyzer.

I have one of my DTR scanning the public channels and got a hit today, heavy traffic during the day, What is interesting is you are listening to the activity but you cannot tell when they are transmitting. The ISM band is full of frequency hopping activity from power meters,etc… and most of it is down in the mud. Whats cool is listening to the chatter but you see nothing out of the ordinary on the screen since it is full of FH activity already and it is invisible in my opinion since I cannot tell when they are transmitting without the DTR monitoring.

I will post a video so you can see the action but its pretty impressive to have something that lets you communicate and have such a low probability of intercept/detection.

now if I transmit next to my setup I will see the hopping but thats because I am a few feet away.

Interesting. I look forward to seeing your video.