PrPr: Flipper Radio Replay 1
Project Progress 1: Radio Replay
A few days ago, I noticed that some consumer electronics such as garage door openers, remote-control outlets, undercabinet lights use frequencies in the subGHz range. 433 MHz, ~800MHz, and a few others are common.
Recently I acquired a Flipper Zero, and in the interest of exploration and curiosity, I decided to look into the prospect of HAM radio's intersection with this capability.
Taking an ARRL Frequency allocation map, my Technician license, and my handheld UHF/VHF radio, I set out to compare the available bands.
I discovered there's actually quite a good bit of overlap from 420 MHz to 450 MHz, and decided on the frequency 433.070.
Testing was simple; once the frequency was selected, I listened for a short period to make sure I wasn't intruding, then called out with my sign asking if the frequency was in use. Hearing nothing, I set the Flipper to record a raw signal on the 433.070 I was transmitting on, and announced "Testing!" a few times.
The Flipper did record something, and when played back was able to overcome the squelch limit on my handheld, so something was being broadcast. Unfortunately, it was either silence or radio static rather than my voice. More attempts were made with similar results.
All modulations were tested; AM270, AM650, FM238, and FM476. FM238 seemed to give the best results, as some definite presence was coming through the radio, however it wasn't speech and instead fluctuations in the strength of the static. This leads me to believe that the FM being transmitted by the radio may have a different modulation than that of the Flipper's best efforts, as transmitting voice and digital signals are slightly different use cases.
Next steps include primarily investigating alternate firmware or altering the firmware myself to allow FM-modulated transmission to match that of my radio.