What type of modulation are they using?

[gmclam]

I've had the FBI frequencies programmed for a while now. What I thought I was hearing was a repeater passing through noise from a receive frequency with no carrier. Then the other day I heard one person in the clear talking to someone who was not. And when the person not in the clear transmitted, I'd hear that same sound; it sounds like RF noise.

Today I picked up the same thing on a Secret Service frequency. So I suspect it is some form of modulation that our scanners are not designed to handle. Can someone tell me what it is?

 

[Avery93]

Most likely DES encryption.

Here is a sample of it.

 

[gmclam]

Yes, the audio sounded the same except for a "beep" near the end of your wav file. I don't hear the beeps, just the noise.

What is the type of modulation used for these transmissions? QAM, PSK, or ???

 

[Squad10]

Yes, the audio sounded the same except for a "beep" near the end of your wav file. I don't hear the beeps, just the noise.

What is the type of modulation used for these transmissions? QAM, PSK, or ???

CVSD is used:

Continuously variable slope delta modulation - Wikipedia, the free encyclopedia