I wanted to see how much traffic the secondary users generate. I used my RTL-SDR dongle with RTL2832U and R820T chips
that I bought on Ebay for less than 10 US$ almost a year ago. The antenna was a roof mounted HL-B61N
vertical (1.7 m long). This is the output of the SDR# program
|Press image for a larger view|
It is clear that this band is pretty busy! No wonder that amateur repeaters have had to move their input frequency away from this frequency range.
The waterfall covers 10-12 seconds and there are up to 10 transmissions simultaneously. The nominal frequency is 433.92 MHz and there are emissions from 433.75 – 434.05 MHz. I live in a suburban area with about 1 million people, but I imagine that I only pick up a small part of the remotes in this area since the car key transmitters are very weak. Anyway it demonstrates both the versatility of the cheap software defined receiver dongle, as well as how busy the band is.